CRC Handbook of Irrigation Technology. Vol. 2 9780849332319, 0849332311, 9780849332326, 084933232X, 9781315893556, 9781351072656

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CRC Handbook of Irrigation Technology Volume II Editor

Herman J. Finkel, Ph.D. Director, Finkel & Finkel Ltd. Consulting Engineers Haifa, Israel

Boca Raton London New York

CRC Press is an imprint of the Taylor & Francis Group, an informa business

First published 1983 by CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 Reissued 2018 by CRC Press © 1983 by CRC Press, Inc. CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www.copyright. com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Main entry under title: Handbook of irrigation technology. Includes bibliographies and index. 1. Irrigation engineering. I. Finkel, Herman J. TC805 .H25  627’.52  80-26417 ISBNO-8493-3231-1 (v. 1 ) ISBN 0-8493-3232-X (v. 2) A Library of Congress record exists under LC control number: 80026417 Publisher’s Note The publisher has gone to great lengths to ensure the quality of this reprint but points out that some imperfections in the original copies may be apparent. Disclaimer The publisher has made every effort to trace copyright holders and welcomes correspondence from those they have been unable to contact. ISBN 13: 978-1-315-89355-6 (hbk) ISBN 13: 978-1-351-07265-6 (ebk) Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

THE EDITOR Herman J. Finkel, Ph.D., is Director of Finkel and Finkel, Consulting Engineers, and Emeritus Professor of Agricultural Engineering of the Technion-Israel Institute of Technology, Haifa, Israel. Dr. Herman J. Finkel is a graduate of the Department of Agricultural Engineering of the University of Illinois (1940) and holds a Ph.D. from the Faculty of Agriculture of the Hebrew University, Jerusalem. After years of experience in the United States with the U.S. Corps of Engineers, the U.S. Soil Conservation Service, and private consulting engineering firms, he moved to Israel where he became the Chief Engineer of the newly formed Israel Soil Conservation Service. This work emphasized water resource development and irrigation. In 1952 he founded the Faculty of Agricultural Engineering at the Technion, Israel Institute of Technology, and served as its head and Dean intermittently for 24 years. During this time he taught and did research in the fields of irrigation and soil and water. From 1969 through 1972 he served as Academic Vice-President for the Technion. During this period, Dr. Finkel maintained an active consulting practice and served as an expert in irrigation for FAO, other international agencies, and private consulting firms in 24 countries of Latin America, the Caribbean, Africa, the Middle East, and the Far East. This activity was divided among design, project evaluation, and training of local staff. He also served on a number of missions of UNESCO and the World Bank on educational planning for the developing countries, as an expert on agricultural and technical education. Since 1972 he has been the head of the consulting firm of Finkel and Finkel, located in Haifa, Israel. This firm has done design work in Israel as well as in Iran, the Caribbean, and Latin America. Dr. Finkel is the author of numerous articles both in his profession and in the more distant fields of history and archeology as well.

ADVISORY BOARD Ilan Amir, D.Sc. Faculty of Agricultural Engineering Technicon—Israel Institute of Technology Haifa, Israel

Shaul Feldman, Ph.D Agronomist Volcani Institute of Agricultural Research Southern Organization Yamit, Israel

DovNir, D.Sc. Professor Agricultural Engineering Department Technicon—Israel Institute of Technology Haifa, Israel

CONTRIBUTORS Ilan Amir, D,Sc. Faculty of Agricultural Engineering Technion—Israel Institute of Technology Haifa, Israel Yaakov Ayalon Agronomist Extension Cotton Specialist Israel Ministry of Agriculture Tel Aviv, Israel Shaul Feldman, Ph.D. Agronomist Volcani Institute of Agricultural Research Southern Organization Yamit, Israel

Herman J. Finkel Professor Emeritus Faculty of Agricultural Engineering Technicon—Israel Institute of Technology Director Finkel & Finkel Consulting Engineers, Ltd. Haifa, Israel Gideon Peri, Ph.D. Scientific Advisor Motorola Israel Haifa, Israel DovNir, D.Sc. Professor Agricultural Engineering Department Technion—Israel Institute of Technology Haifa, Israel

CONTENTS Volume I The Importance and Extent of Irrigation in the World Soil-Water Relationships Plant-Water Relationships Water Requirements of Crops and Irrigation Rates Soil Salinity and Water Quality Hydraulics of Open Channels Measuring Channel Flow Pipe Flow Sprinkler Irrigation Drip Irrigation Pumps and Pumping Gravity Irrigation Index Volume II Land Grading Drainage of Irrigated Fields Criteria for the Choice of Irrigation Method Health Hazards of Irrigation Economics and Costing of Irrigation Automated Computerized Irrigation Irrigation Management and Scheduling Irrigation of Cotton Irrigation of Sugar Crops Irrigation of Oil Crops Irrigation of Cereal Crops Irrigation of Alfalfa Irrigation of Citrus Index

TABLE OF CONTENTS Volume II Land Grading

1

Drainage of Irrigated Fields

13

Criteria for the Choice of Irrigation Method

35

Health Hazards of Irrigation

47

Economics and Costing of Irrigation

61

Automated Computerized Irrigation

77

Irrigation Management and Scheduling

91

Irrigation of Cotton

105

Irrigation of Sugar Crops

119

Irrigation of Oil Crops

137

Irrigation of Cereal Crops

159

Irrigation of Alfalfa

191

Irrigation of Citrus

199

Index

215

Volume II

I

LAND GRADING Dov Nir

GENERAL Most natural soil surfaces, as well as many cultivated fields, are more or less irregular, consisting of alternating depressions and elevated areas. This results in pondage of water and interrupted surface drainage on one hand, and in accelerated soil erosion on the other; other effects may be nonuniformity of yield and crop quality, difficulties in mechanized field operations, as well as inadequate drainage. Under irrigated conditions, surface irregularity is even more harmful. Gravity irrigation methods require even and continuous overland flows over nonexcessive slopes, in order to provide uniform wetting of the root zone, decrease deep percolation losses, and prevent soil erosion. Even when sprinkler (or trickle) irrigation is used, irregular soil surfaces may cause nonuniformity of wetting and surface pondage. Consequently, in most cases it is advisable to re-form the land surface so as to provide continuous, gentle slopes, regulated water flows, and adequate drainage. This is expensive and therefore must be well-designed, carefully executed, and constantly maintained. Design should take into account soil type and depth, natural slopes and drainage system, and the method of irrigation to be employed. The following three main types of land forming are used: 1.

2.

3.

Land leveling is creating an almost horizontal soil surface, sometimes in the form of bordered basins, with not more than 0.5% slope in the direction of cultivation, and at most 1% at right angles to this direction. This conserves water and helps in flood control, and is used both under irrigation and dry farming conditions. Land grading provides a continuous sloping plane surface in the graded plot. Generally the slope would not exceed 5% and will remain roughly parallel to the original general slope of the field; this would help decrease the amount of soil to be moved. A method of land-grading design will be presented here; this includes, as a particular case, the design of land leveling as well. Land smoothing is a means of removing local elevations and filling local depressions, in order to permit continuous surface water flow to the field outlet. This is done with no calculated design — with the implement (generally, bulldozer) operator using his keen eye, good judgment, and past experience to guide him in the efficient execution of his work. This consists of a rough lowering of elevations and filling of depressions, followed by two to four fine smoothings in different directions. WHEN NOT TO GRADE

Grading should not be done when: (1) soil (infiltration, slopes, depth, etc.) and water (discharge) conditions counterindicate surface irrigation, (2) soil is shallow; and (3) topography is so irregular that grading would require excessive earthmoving and will be too expensive. In general, movement of more than some 1500 mVha would be considered too costly. PRINCIPLES OF LAND GRADING 1.

Minimum of earth moving

2 2. 3. 4. 5.

CRC Handbook of Irrigation Technology No cut to exceed a certain maximum (about 15 cm); if in some points this principle is not adhered to, the exposed soil should be fertilized or covered with stripped topsoil Minimum haul distances Cut should exceed fill by 15 to 50%. This is due to compaction during fill, transportation losses, and soil crowning near the stakes. (Generally a 20 to 30% shrinkage factor is indicated) Maximum convenience and efficiency in the operator's work

EQUIPMENT Grading equipment consists of various types of machines, either self-propelled or hitched to tractors (crawler or wheeled). Heavy work is generally done by scrapers (or bulldozers, for short hauls and stony soils); finer grading and smoothing are best done by graders and land planes, or even by animal-drawn floats. See Figures 1, 2, and 3. During the 1970s a significant advance in land grading has been achieved by the introduction of laser-operated controls, allowing a higher level of accuracy and efficiency of operation. A rotating laser beam (at 10 to 300 rpm) defines a control reference plane; this is "read*' by a 360° sensor on the equipment's cab which automatically controls its operation by means of a direct link to its hydraulic system. More than one machine (each with its own sensor) can use a single laser source to distances exceeding 0.5 km, even in daytime.

STEPS FOR LAND GRADING 1. 2. 3. 4.

5. 6.

Decide on a suitable irrigation method according to surface conditions, soil type, crops and rotation, manpower, water availability (amounts, discharge, quality), local usage, etc. Divide the field into plots according to size, alignment of farm roads and waterways, and local slopes. Each plot will be graded as one unit. Determine required or permissible slopes, both in the direction of cultivation and in the cross-direction. Stake the area, preferably at a square grid of 10 to 25 m in each direction. The more irregular the topography, the smaller the squares. Stakes should be 120 cm long, 2.5 x 2.5 cm in section, and should be driven into the ground to a depth of 30 to 40 cm. Survey the plot by means of a surveyor's level, determining surface elevations at each stake and at other outstanding points (where topography changes abruptly), surveying should be done on cleared, unplowed ground. Prepare a topographical map to a 1:500 to 1:1000 scale (according to the irregularity of the topography). Contour lines should be drawn at vertical intervals of about 15 cm per each 1% of general slope, so that they will be 1 to 2 cm distant from one another on the map. Generally a vertical interval of 10 cm is used on flat lands and 25 cm on medium slopes. It is advisable to reduce elevation readings by using a new datum (rather than that of Mean Sea Level), a little lower than the lowest point of the area, or of the plot outlet.

At each grid point elevations should be marked above and to the right of the point, thus:

Volume II

3

FIGURE 1. Land plane.

FIGURE 2.

Motor grader.

FIGURE 3. Tractor-drawn scraper.

Figure 4 is an example of such a topographical map, with contours at a vertical interval of 10 cm and elevations marked at each grid point. This map will be used later for illustrating the leveling design process.

DESIGN OF GRADING One of the most efficient and widely used methods for grading design is the leastsquares method, due to Givan1 and Chugg2 and presented by J. C. Marr. 3 Using this method, a plane is designed such that the sum of the squares of its deviations from the original surface would be minimum, and that (as a first stage) cut will equal fill. The following sections show the steps by which the design is done.

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CRC Handbook of Irrigation Technology

Surveying and Mapping For convenience in calculations, the staking is done so that the first row and column of the square grid are one half station (a *'station" corresponds to the distance between stakes) from the edge of the plot. Thus each point represents a whole square, of one square station area. The grid points are numbered from 1 to m in the x (say west to east) direction and from 1 to n in the y (say north to south) direction (see Figure 5). In a rectangular plot there would be m x n grid points, covering an area of m x n square stations. Determining the Plot's Centroid (or *'Center of Gravity") The centroid (C) is located in the middle of the area, determined in a rectangular area by marking the crossing point of both diagonals, or by calculating xc = 1/2 (m + 1)

y c - 1/2 ( n + 1 )

and in areas of nonrectangular shapes by taking moments around any selected point, preferably at or outside one of the corners of the plot. If moments are taken about the origin (this would be the point [O,O] located one half station outside the plot, above and to the left of the corner near stake [1,1]), then

when t is the total number of the grid points [x(y,]. The elevation of the centroid is given by

where h, is the elevation of the grid point [x(y,]. It is not the ground elevation at point C! Determining Average Profiles and Average Slopes In this step we shall determine the average profile of the plot in each direction x and y, and find the average slopes in these two directions, such that the sum of squares of deviations of the average slope line from the average profile will be minimum (i.e., cut and fill will be minimum). For a rectangular plot, this is calculated as follows. Stepl Prepare an elevation table as shown in Table 1, and calculate: marginal sums I, and Zy; marginal averages H* and Hy; weighted averages xH, and yHy, where

FIGURE 4.

Example of topographic map.

In this table:

The elevation table for the example presented in Figure 4 will be as shown in Table 2. Step 2 The values of marginal averages, H* and Hy, constitute the average profiles of the area in the x and y directions, respectively. Compute the average slope for each profile by means of the formulas

6

CRC Handbook of Irrigation Technology

FIGURE 5.

Average slopes.

where a(m) = 1/2 (m + 1); b(m) = m(m 2 - 1)/12 (see Table 3 for values of a and b). In the example, a(m) = a(5) = 3 b(m) = b(5) = 10

a(n) = a(4) = 2.5 b(n) = b(4) = 5

and

Positive slope values indicate slopes rising from the origin outward. The profiles for the example, as well as the computed average slopes (which, for equalizing cut and fill, must pass through the centroid), are shown in Figure 5 (a and b). Check whether the average slopes conform to the maximum and/or minimum values, determined in "Steps for Land Grading" #3. If the slope in either direction is found to be outside the permissible range, modify its value to that of the nearest limit. Step 3 Determine the graded elevation of the origin, using the modified values of S, and Sy, by means of h

o * hc - xcSx - ^y

Volume II Table 1 ELEVATION TABLE — GENERAL

\x

y\

1

2

3

—

m

i

h,, hI2

h 21 h 22

h31 h32

—

hml h m2

I' I2

IH> IH 2

1H' 2H 2

hlrt Ii H, 1H,,

h 2n I, H2 2H 2

h 3n I3 H3 3H3

— — —

h mn Xm Hm mH m

I" T 2H, IxH,

IH" IH*

nH" lyH>-

2 n

Table 2 ELEVATION TABLE — CALCULATION

V

y\

i 2 3 4

1

2

3

4

5

0.20 0.32 0.43 0.50 1.45 0.36 0.36

0.30 0.25 0.33 0.42 1.30 0.33 0.65

0.38 0.30 0.33 0.37 1.38 0.35 1.04

0.47 0.43 0.37 0.35 1.62 0.40 1.62

0.60 0.50 0.45 0.42 1.97 0.49 2.46

1.95 1.80 1.91 2.06 27.72 1.93 6.13

Table 3 VALUES OF a AND b morn 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

a(m) or a(n)

1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 15.5

b(m) or b(n)

0 0.5 2 5 10 17.5 28 42 60 82.5 110 143 182 227.5 280 340 408 484.5 570 665 770 885.5 1012 1150 1300 1462.5 1638 1827 2030 2247.5

0.39 0.36 0.38 0.41 1.54

0.39 0.72 1.15 1.65 3.91

1

8

CRC Handbook of Irrigation Technology Table 4 0.30

0.38

0.47

£^3- Q.Q3F 0.32 0.02F

^37 o.oic 0.36 0.02C

^ua

0.32

0.25

0.30

0.43

0^4- 0.01C 0.30 0.02C

£^5- 0.10F 0.34 0.09F

0.43

0.33

0.33

4X32 o.nc 0.31 0.12C

&&> 0 03P 0.35 0.02F

039

0.50

0.42

0.37

0.35

0.42

&&- ^).05C 0.36 0.06C

4MO 4XOSF 0.39 0.02F

0.5 250

0.15' 35' 20' 30' 0.5*

30

25

Indicator

— _

0.5 15 10 15 0.5 — —

Note: Standard is based on 80% of the samples. Group A: cotton, sugar beets, grains, dry fodder, seeds. 6 Group B: green fodder, olives, peanuts, citrus, bananas, almonds, nuts. c Group C: deciduous fruits, vegetables for canning, vegetables for cooking, peeled vegetables. d Group D: crops with no limitation, lawns, parks. e Under-crown irrigation, up to 2 weeks before harvest; gathering windfalls forbidden. f Excluding oxidation ponds with minimum retention of 10 days. * Excluding oxidation ponds with minimum retention of 15 days. 0

may make the cost of the recycled water so expensive as to place it beyond the limit which agriculture can pay. If this happens, the entire project becomes inoperable and nothing results but a well-written standard. It has been found advisable in developing countries to begin the control with less rigorous standards, and as the need becomes evident and as the agricultural economy becomes stronger, the standards be gradually raised. This requires alertness and watchfulness on the part of the health authorities to recognize unfavorable developments as early as possible. The second point to bear in mind before a standard is adopted is the problem of enforcement. If sewage effluent of a certain standard is permitted on only certain types of crops, supervision must be provided to ensure that this will not be violated in the course of the subsequent crop rotations. Moreover, great care must be exercized to prevent cross-connections and any possibility that the effluent of low standard be used for drinking, laundering, or other domestic purposes. Not all developing countries have adequately staffed supervision agencies to ensure compliance with the standards. For these reasons the first projects undertaken in sewage irrigation should be carefully selected with respect to type of crop, standard of effluent, and location with respect to other fields and residential areas, so as to minimize the above described hazards. During the period of development of such projects, the supervising agencies can gain experience and improve their organizational abilities to handle more problematic or hazardous situations. POLLUTION OF GROUND WATER One of the detrimental effects of irrigation may be the pollution of the ground water by the leaching of pollutants from the soil and the surface. The most common pollu-

54

CRC Handbook of Irrigation Technology

tants are nitrogen compounds and pesticides. Other types of pollution such as bacteria, viruses, etc. may also occur, but these will generally originate from surface sources other than irrigated agriculture. The basic mechanism of ground water pollution is the downward movement of water and pollutants (leaching) resulting from their application in excess of the ability of the plants and the surface soil to retain and utilize. The amounts and extent of these surpluses are directly proportional to the extent, intensity, and length of history of the irrigated agriculture. This can best be illustrated by data from some of the modern, intensively developed irrigated areas of the world. Nitrogen Compounds The most common form of ground water pollution with nitrogen is by the inorganic compounds of nitrates, nitrites, and to a lesser extent, ammonia. Nitrate has been commonly accepted as the most monitored parameter of this type of pollution. The nature of the nitrate hazards has been well summarized by Ayers and Branson:2 The hazard of high nitrate to infants and livestock is illustrated by a disease known as methemoglobinemia or nitrate cyanosis which is caused by nitrite formed by reduction of nitrate in the intestinal tract. Nitrite enters the blood stream and combines with hemoglobin to form methemoglobin thus reducing the blood's capacity to transport oxygen. This reduction to nitrite occurs in infants because their gastric juices are more nearly neutral than those of adults which have an acidic balance Similar nitrate-nitrite poisoning effects have been noted in ruminants (such as cattle) at concentration levels in waters exceeding 2000 ppm nitrate.

Standards for nitrate limitation in drinking water are not uniform. The U.S. Public Health Service in 1962 recommended a limit of 45 ppm nitrate or 10 ppm N. At this concentration the public is to be warned of the potential dangers of using the water for infant feeding. California has a recommended limit of 45 ppm nitrate and a mandatory limit of 90 ppm. There seems, however, to be considerable uncertainty over the scientific validity of these nitrogen standards. The amounts of nitrogen which are leached down to the ground water can be estimated from the efficiency factors for irrigation and fertilization. It is commonly recognized that surface methods of irrigation, as practiced in many countries, are from about 25 to 50% efficient. This means that from 50 to 75% of the water is not retained in the plant-root zone and is lost either by evaporation (about 10%) or by deep seepage (all the rest). This seepage usually reaches the water table. With sprinkler irrigation, however, efficiencies of water application may reach 65 to 70%, which means that the losses to deep seepage may be of the order of 20 to 25%. The most modern system of drip irrigation would, of course, have even lower losses, and consequently less seepage to the water table. Efficiencies of utilization of fertilizers by the plants have been estimated to range from 10 to 30%, which means that from 70 to 90% of the nitrogenous matter may be lost. A portion of this goes to the ground water. Some data from the Upper Santa Ana River Basin (Calif.) may serve to illustrate this problem2 (see Table 3). It can be seen that in this region of intensive irrigated agriculture in the course of 39 years the cultivated area increased by 56%, the total applied N by 9 times, the N per acre by 6 times, and the excess N (application less crop removal) by 30 times. The trend gives a clear warning to the less developed regions which are embarking upon programs of intensive irrigation. Pesticides The use of herbicides, fungicides, and insecticides has increased tremendously in recent years, especially for agriculture under irrigation. In the U.S., for example, in 1971 over 158 million acres of land were treated with herbicides, 65 million acres were treated with insecticides, and almost 7.5 million with fungicides.19 Studies of their ef-

Volume II

55

Table 3 ACREAGE ESTIMATED NITROGEN APPLICATION, AND ESTIMATED NITROGEN REMOVAL OF VEGETABLES IN RIVERSIDE COUNTY, CALIF. 1930 TO 1969

Year

Acres

Total N application (10,000 Ibs)

1930 1969

1971 3078

59 539

N (Ib/acre)

Total N removed in crops (1000 Ib)

Excess N (1000 Ib)

30 180

48 209

11 330

feet upon pollution have dealt more with surface runoff, but there are good reasons to fear that some of the residuals may reach the ground water table under a regime of excessive irrigation and leaching for salinity control. Some 78 different commercial herbicides, 63 insecticides, and 28 fungicides are reported by Stewart with respect to their toxicity, their method of transport, and their persistence in the soil. His conclusions with respect to percolation to the ground water are that except in regions of high potential percolation (humid regions), the probability of contamination of the aquifers is low. However, it can be countered that under a regime of heavy irrigation applications, either because of inefficient use of water or deliberately for purpose of leaching out salts from the soil, a significant amount of residual pesticide might reach the ground water. The persistence of the herbicides in the soil varies tremendously from 10 days for 24D® to 700 days for Benefin®, Fenac® and Terbacil®. There are no clearly established standards for tolerances or limits of the various insecticides in the drinking water, but values for lethal dosages and lethal concentrations of each type of pesticide have been determined and reported in the literature. As far as control measures are concerned, where pesticide contamination of the ground water is suspected, the wells should be monitored. If high concentrations are found, the use of the pesticide should either be stopped or its application should be carefully timed not to be followed by heavy irrigations until the residual time has elapsed. Examples of Ground Water Pollution It is interesting to examine illustrative examples from the coastal plain region of Israel, because this is an area of relatively light soil overlying one of the most important aquifers in the country. All of the available water is pumped for intensive irrigation, mostly of citrus orchards. The developments in this region can, consequently, serve as an indication (or a warning) of what may lie ahead in other arid and semiarid countries which are just beginning to develop their irrigation potential (data below from Saliternik 14 ). In 1955, the overall average of nitrate concentration in all the wells was 16 mg/l. This rose to 34 mg/j? in 1965. In the area around the cities of Rishon and Rehovoth, 60% of the wells had concentrations of nitrate above the allowable 45 mg/l and 10% of the wells exceeded 100 mg/l. By 1970, 50% of the wells were above the allowable standard and 88 wells were above 100 mg/l. It is estimated that half of the nitrogen originated from agricultural fertilizers and irrigation water, and the remainder from other sources (animal wastes, sewage, rain, etc.) The contribution of nitrogen to the ground water is estimated to be from 10 to 25 kg/ha from uncultivated land, 80 kg/ ha from cultivated, nonirrigated land, and 460 kg/ha from irrigated land on the light soils of the Coastal Plain.

56

CRC Handbook of Irrigation Technology

It is noteworthy, however, that despite these alarming concentrations of nitrates in the ground water, there has not been a significant increase of incidence of methemoglobinemia in the infants of this district as compared to other parts of Israel. This is explained by the following: infants in Israel are generally fed very little water. They are either breastfed or given whole cow's milk, but not milk reconstituted from powder and local water. They are also given quantities of fresh orange juice and the vitamin C helps counteract the disease. POLLUTION OF SURFACE RUNOFF

All of the pollutants discussed in the section "Pollution of Ground Water'* — nitrates, nitrites, and pesticides — may also appear in the surface runoff flowing from the irrigated fields and cause pollution in the drainage canals, streams, and lakes. Irrigation return flow water, passing through the soil and collected in the drainage systems, will cause similar pollution in the recipient bodies. Surface runoff under irrigation is caused primarily by incorrectly designed and operated irrigation systems in which the rate of application of water exceeds the infiltration rate of the soil. This would appear to be a relatively simple matter to correct and indeed it is when sprinkler systems are used. However, under the more primitive gravity methods (wild flooding, borders, and furrows), control of application rates is much more difficult to achieve. Furthermore, some of the systems actually require a certain amount of outflow from the lower ends of the borders and furrows to achieve the required minimum average water application along the entire length of the run. Excessive water application, either unintentionally because of poor techniques or deliberately for purposes of flushing out salts, will also give rise to increased drainage flow. The principal ways in which these pollutants might cause harm are to the quality of drinking water (both for humans and for animals) which may be drawn from the recipient streams and lakes, and to the fish and other wildlife. A few examples will be given. Nitrates The Santa Ana River (Calif.) flows through a region of intensive irrigated agriculture (described in above section). At one measuring station (below the Prado Dam) the nitrate concentration rose from about 6 ppm in 1930 to over 30 ppm in 1965. At other stations on the same river the nitrate concentration fluctuated greatly with some tests reaching 99 ppm. The actual concentrations depended upon the amounts and concentrations of the irrigation water return flow and on the total streamflow discharge. In some cases high concentrations of nitrate in the river coincided with low total discharge and in other cases the opposite was true. Studies made on the Colorado River (U.S.) from 1942 to 1961 have shown that the total salt concentration reached an average of close to 700 ppm. Of this 253 mg/i or 37% was attributed to irrigation. A thorough and detailed study was made by Sylvester and Seabloom20 of the effect of irrigation return flow on the quality of the Yakima River in the state of Washington (U.S.). The Yakima River Valley drains an area of 15,850 km 2 , including some 152,000 to 182,000 ha of irrigated land. In addition, the river receives treated sewage from a population of 80,000 persons. Among their findings were the following: 1. 2.

Irrigation return flow was the major factor influencing the overall water quality of the Yakima River as compared with domestic sewage and industrial waste discharges. Leaching was the primary process responsible for the increase or change in the quantity and composition of salts in the return flow water.

Volume II 3.

57

Chemical constituent increases of particular note occurring in the subsurface drainage water because of evapotranspiration, leaching, and ion exchange, expressed as number of times greater than in the applied water were as follows: bicarbonate alkalinity, 4.8; chlorides, 12; nitrate, 10; sulfate, 7.2; sodium, 0.2; potassium, 3.4; soluble phosphate, 3.2; and calcium, 4.3.

Pesticides Regarding the concentration of pesticides in surface runoff from agricultural areas, Stewart19 has concluded that: Many investigations of losses of various agricultural pesticides in runoff from treated land have been reported. Nearly all lead to the same general conclusion: except where heavy rainfall occurs shortly after treatment, concentrations are very low and the total amount of pesticide that runs off the land during the crop year is less, often much less, than 5% of the application. Nevertheless, many agricultural chemicals are highly toxic to fish or other aquatic fauna, and can persist in the aquatic environment for a long time so that even very low levels of these pesticides in runoff may be of environmental concern. In evaluating the potential environmental impact of specific pesticides in runoff, persistence and toxicity should be considered together because a toxic compound that rapidly degrades will pose only a temporary hazard when residues are transported from treated areas. Pesticide residues dissolved in runoff water are more difficult to control and move greater distances in drainage streams than those absorbed on sediments; hence, they are potentially more hazardous to the environment.

However, one should bear in mind that the above conclusions have not taken into account the effects of heavy applications of irrigation water. This is equivalent to heavy rainfall, and may be even more effective since it generally coincides with the application of pesticides. The deleterious effect of pesticides in the runoff water may be felt in several ways. If the river water is used at any point downstream for human water supply, the necessary treatment would have to include the removal of the toxic materials. This is difficult to accomplish and may be quite expensive. The pesticides will, in all probability, also be toxic to fish and other aquatic organisms in the stream and will either cause their destruction or the accumulation of toxic residues in their bodies. This would render them unfit for human consumption. OVERIRRIGATION One of the basic hazards in irrigation is the excessive use of water. When the quantities of water applied exceed the needs of the crops and the retention capacity of the upper layers of the soil, the surplus is disposed of in one of two ways; either it moves downward and enters the ground water table, or, if an adequate drainage system is provided, it moves laterally to some suitable outlet such as a river or the sea. In the past it was not customary to install an adequate drainage network at the time of constructing the irrigation system, and consequently the water generally moved downward. This resulted in a gradual rise of the water table, which in many areas reached alarming proportions. There are examples of this condition in many countries. In the upper part of the Jordan Valley, water was diverted to irrigate banana plantations by a gravity system with the surplus flowing back into the river. In the course of 25 years the phreatic surface (as the water table is called) rose by almost 40 m and came within a meter of the land surface. A system of deep drainage ditches had to be installed to correct the conditions.

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In the Shabankareh area near Boushehr, Iran, an extensive date palm plantation was similarly irrigated through a system of diversion canals causing the water table to rise from about 10 m deep to the land surface over the course of about 20 years. This was further aggravated by the fact that the river water was itself saline because of return-flow from another extensive irrigation project located upstream. Unfortunately, this problem had not been anticipated and the trees had been planted in such a way as to allow almost no possibility of cutting drainage ditches through the area without uprooting many palms. The entire plantation of about 20,000 ha is now threatened with destruction.

REFERENCES 1. Ashboren, D., Ed., Recycling of Waste Water for Agricultural and Industrial Uses, Proc. Jt. Isr.-S. Afr. Syrup. Herzliya, Isr., November 1975, National Council for Research and Development, Jerusalem, 1976,62. 2. Ayers, R. S. and Branson, R. L., Nitrates in the upper Santa Ana River Basin in relation to ground water pollution, Calif. Agric. Exp. Stn. Bull., 861, 1973. 3. Brackish Water Desalination and Waste Water Recycling, project report by Center for Tech. Forecasting of Tel Aviv Univ., National Council for Research and Development, Jerusalem, 1975. 4. Critchfield, R., Snails carry bilharzia across the Nile, disease reaches plague proportions, (OFNS report), Jerusalem Post, 44, 5, 1976. 5. Faust, E. C., Animal Agents and Vectors in Human Disease, Lea & Febiger, Philadelphia, 1955. 6. Fitzsimmons, D. W., Lewis, G. C., Naylor, D. V., and Busch, J. R., Nitrogen, phosphorous and other inorganic materials in waters in a gravity irrigated area, Trans. A.S.A.E.,292, 1972. 7. Greenberg, A. E. and Dean, B. H., The beef tapeworm, measly leef and sewage: a review, Sewage Ind. Wastes, 30, 262, 1958. 8. Greenberg, A. E. and Kupka, E., Tuberculosis transmission by wastewaters: a review, Sewage Ind. Wastes, 29, 524, 1957. 9. Ground Water Pollution. II. Pollution From Irrigation and Fertilization, citations from NTIS Data Base, Natl.Tech. Inf. Serv.,U.S. Department of Commerce, Springfield, Va., 1964 to 1977. 10. Kerr, R. S., Nutrient, Bacterial and Virus Control as Related to Ground-Water Contamination, Publ. No. EPA-600/8-77-010, Environ. Res. Lab. of Res. and Dev., U.S. Environ. Prot. Agency, Ada, Okla., July 1977. 11. Kloos, H. and Lemma, A., Bilharziasis in the Awash Valley, Ethiopian Med. J., 12, 157, 1974. 12. Elwi, A. M.,Pathological Aspects of Bilharziasis in Egypt, Mostofi, F. K., Ed., Springer-Verlag, Berlin, 1967,38. 13. Hazards of nitrate, nitrite, and nitrosamines to man and livestock, in Accumulation of Nitrate, National Academy of Sciences, Washington, D.C., 1972. 14. Saliternik, C., Water Quality in Israel, report of the committee on water quality, Isr. Natl. Comm. Biosphere and Environ. National Council for Research and Development, Jerusalem, 1973. 15. Shuval, H., The Effects on Man and Animal of Ingesting Nitrates and Nitrites in Water and Food, paper for panel on isotope tracer-aided studies of the fate and significance of agro-chemical residues in soil with particular reference to nitrates, International Atomic Energy Agency — FAO, Vienna, June 1973. 16. Shuval, H., Epidemiological and toxicological aspects of nitrates and nitrites in the environment, Am. J. Public Health, 62, 1045, 1972. 17. Silverman, P. H. and Griffiths, R. B., Review of methods of sewage disposal in Great Britain with special reference to epizootiology of Cysticercus bovis, Ann. Trop. Med. Parisitol.,49, 436, 1955. 18. Sorber, C. A. et al., Virus survival following wastewater spray irrigation of sandy soils, in Virus Survival in Water and Wastewater Systems, University of Texas, Austin, 1974. 19. Stewart, B. A., Woolhiser, D. A., Wisch Meier, W. H., Caro, J. H., and Frere, M. H., Control of Water Pollution from Cropland, Vol. 1, A Manual for Guideline Development, E.P.A., Office of Research and Development; Vol. 2, An Overview, Agricultural Research Service, U.S. Department of Agriculture, November 1975.

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20. Sylvester, R. O. and Seabloom, R. W., Quality and significance of irrigation flows, J. Irrig. Drain. Div. A.S.C.E.,89(3), 1, 1963. 21. Todd, D. K. and McNulty, D. E. O., Polluted Groundwater. A review of the Significant Literature, Water Information Center, Huntington, N.Y., 1976. 22. WHO Reuse of Effluents: Methods of Wastewater Treatment and Health Safeguards, Tech. Rep. Ser. No. 517, World Health Organization, Geneva, 1973. 23. Shuval, H. I., Health considerations in water renovation and re-use, in Water Renovation and Reuse, Shuval, H., Ed., Academic Press, New York, 1977, 33,

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ECONOMICS AND COSTING OF IRRIGATION Dov Nir

INTRODUCTION Agricultural practice should be considered as a business, which is economically justifiable only when it shows a profit. Water is one of the major inputs of agriculture and in many cases may prove to be the limiting factor in an agricultural system. It is therefore important that any irrigation project be fully analyzed from the economic viewpoint and shown to be profitable, so that its output should have a clearly higher value than the sum total of all inputs. Moreover, any separable subsystem of such a project (i.e., any part of the project which may be included or excluded from the project without changing the feasibility of the rest of the system) should be able to pass this test and be shown to be economically justifiable, or else should be rejected. Thus, the economic evaluation of such a system should be based on a comparison of total benefits to total costs. Utmost care should be taken to include in the calculations all benefits resulting from the operation of the system, including — in addition to the main product itself — all by-products, such as straw or green manure, and even negative outputs, such as pollution by drainage water (which must be controlled) or waste disposal. Also to be included are all indirect benefits, both quantifiable as well as intangible (such as the changes in employment patterns or in length of growing season). Intangible benefits will be included by expressing them quantitatively, using the willingness-to-pay principle. This means estimating the amount the recipient of a benefit will be ready to pay in order to be sure of receiving it. Sometimes it is also possible to estimate the cost of providing the same benefit using an alternative method, and to take this cost as the value of the benefit. Costs, too, should include all inputs into the system — land and water, materials and equipment, manpower and know-how, managenent and organization, etc. STEPS IN ECONOMIC ANALYSIS Economic analysis consists of three main steps. Determination of Feasibility Any project and any separable subproject must be economically justifiable. The total of its benefits ( = B) should be more than the total of its costs ( = C). This is written in the forms B > C, B - C > O, or B/C > 1; all three are — for this purpose — equivalent, and show the feasibility of the project under study. It is important to take into consideration the time element of both benefits and costs: some of the costs are incurred at the early stages of the project—planning and design, installation and running-in, etc. Others are paid annually. These are the OMR (Operation, Maintenance, Replacement) costs, as well as taxes, insurance, etc. Benefits are generally obtained annually. For a comparison of benefits and costs, both should be expressed in the same terms — either as present-worth values or, alternatively, as annual values, including, also, amortization on the initial investment. In Appendix A to this chapter, principles and methods of accounting for the timeelement are summarized. Ranking When more than one project have to compete for a limited budget, or when various alternative projects are submitted as solutions for the same problems (such as irrigation by different methods), they have to be compared and arranged in a series of decreasing

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values, such as decreasing net benefits, decreasing profit on invested money, etc. The result is a ranking or priority list. Under financial constraints, i.e., when money is scarce, not all economically justified, or feasible, projects will be implemented, but only those that are highest on the ranking list. When alternatives to achieve the same goal are considered, the highest ranking projects will be chosen that, together, have the required total size. In comparing benefits to costs, there exists an important difficulty which must be fully recognized and answered: whether projects should be ranked according to net benefits, i.e., B - C, or to relative benefits, i.e., B/C? The first approach clearly gives preference to larger projects, where the total net profit would be high, even if the profit per unit of investment is small. The second approach selects those projects which give maximum returns on each invested money unit. These are the most efficient projects, from the viewpoint of making the best use of the inputs into the system. Under conditions of scarce resources and especially of limited supply of money, it is advisable to use the B/C criterion, which will allocate these resources to a combination of smaller, efficient projects, rather than to one or two larger ones. When resources are not limiting factors and are available for use, large systems with high net benefits will be preferred and the B - C criterion used. Irrigation projects planned for arid or semiarid conditions are generally constrained by the scarcity of water (and, in many cases, also of land, capital, and other resources), and should be ranked by the B/C criterion, taking care to use realistic values for the costs, especially of the limiting factors. Sizing The optimal size of a selected project is also determined by comparing benefits to costs. The analysis is best explained with the help of a graphical representation. Figure 1 shows a typical benefit-cost curve, where the size of the project is represented by the cost ordinate, and a 45° line shows equality of benefits to costs. It is clearly seen that any project of size larger than that represented by point d or smaller than that represented by point a is economically unjustified: B is smaller than C. The project size is therefore limited to the range a to d. A closer look can make the range still narrower. The point marked b, which is the tangency point with a ray from the origin, is the point of maximum B/C. Point c, the tangency point with a 45° (B = C) line, is the point of maximum B - C. From that point upwards, increases in benefits are smaller than the corresponding increases in costs. Any project smaller than that represented by point b can be improved, according to both B/C andB - C criteria, by approaching point b. Similarly, any project larger than point c would be better, according to both criteria, if it were reduced to the size represented by point c. Hence, the optimal size must be within the range b to c. Projects in the feasible range c to d would be justified only when mere size is an asset, too (for example, when large-size systems can draw funds from sources [government, international, or foundation] which do not deal with small projects). When capital is scarce, optimal project size would be determined by the point b, which will give maximum returns on the costs. When available funds are enough for more than one project, but not enough for the optimal size ("b") of all of them, the best investment policy consists of sizing the individual projects so as to equalize the marginalB/C values. Thus the cutoff point for N such projects is defined by:

when C, = total available funds.

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FIGURE 1. Typical benefit-cost curve.

Internal Rate of Return The inherent profitability of a system or of a subsystem, or, in other words, its efficiency, may also be measured by means of a comparison between benefits and costs, through the use of the internal rate of return, r. This is defined as that interest rate which will provide for equalization of total costs to total benefits. If we take annual values, we can write this equality as (see Appendix A): P x CRF + A = B

where P = initial investment; A = annual costs; B = annual benefits; CRF = capital recovery factor. This can also be written as: P x CRF = B - A

where B - A = annual net benefits or

Then the internal rate of return of the system, r, is that rate of interest which will satisfy

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or, conversely

This value can also be used for economic analysis of projects. If r is higher than the market rate of interest, the project would be economically justified. Otherwise, the money would be better invested elsewhere in the open market. When it comes to ranking, the use of the internal rate of return is more problematic. It can be shown that ranking by this method (the higher the r, the better) will give a different series than that obtained by using the B/C criterion. Its use is advisable when money for the initial investment is hard to get. Both criteria will give similar ranking when comparing projects with similar capital intensities, i.e., with similar A/P ratios. ENUMERATION AND EVALUATION OF COSTS AND BENEFITS The main point to be remembered in making an economic analysis of irrigation projects is that all costs and all benefits should be included in the analysis. This point is important in all economic work; but while in industrial and service enterprises full enumeration of these elements is comparatively easy, in agricultural projects and especially in water projects, this is much more difficult and requires most careful study. There are so many interrelationships between the project and its environment on one hand, and so many uncertainties in the system's inputs and outputs on the other hand, that many items can quite easily be overlooked — accidentally or intentionally. In the following paragraphs the main items of costs and benefits in irrigation projects will be listed. These lists are, of course, by no means exhaustive and complete, but may help in presenting approaches and principles. Irrigation Costs Investment, Initial, or Fixed Costs The extent and importance of this element of total cost depends mainly on whether the system provides its own water supply or receives water as an input from another system. In the latter case, water cost appears as an operation item in annual costs, with its price dictated by factors outside the system. For the sake of completeness, it will be assumed that the system supplies its own water. Investment costs will thus include: Planning and design costs Land purchase, translocation of rural population Right-of-way for water conveyance Office space (if necessary) Water supply Dam and reservoir, or Well Pumping unit (ace. to required head and discharge) Generator, or Connection to electricity grid; transformer Motor Pump(s) Switching and control equipment Monitoring, metering, and recording equipment Automation equipment/remote control

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Filtering; chlorination; water quality monitoring Pumphouse; fencing; landscaping Roads; parking; etc. Water conveyance Canals Lined or unlined, or Pipes Material Laying Fittings and equipment Valves and gates Control and monitoring — automatic? Metering at outlets Bridges and culverts; drainage of unlined canals Irrigation system Surveying Land grading and preparation Field distribution system Ditches or pipes (portable, fixed) Control equipment; valves Irrigation equipment "Ames" gated pipes Hydrants Sprinklers Tricklers (drippers) Anchors, stands, etc. Other fittings; spare parts Storage facilities for out-of-season storage Automation equipment Meteorological station Soil-moisture monitoring equipment Drainage system (usually required) Surface drainage; vegetated waterways Subsurface drainage Outlets Annual Operation Costs Again, if the system does not supply its own water, the main operation cost will be payment for water. Otherwise: Water supply and conveyance Fuel or electricity Maintenance of subsystem: oil, parts replacement, minor repairs, painting Taxes and insurance Replacement of short-lived elements Periodic check-up of fittings and meters Operating manpower Irrigation system Maintenance and repair of equipment Renewal of borders and ridges; regrading Changing from one irrigation method to another Operating manpower Office work: management, bookkeeping Maintenance of drainage system

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It is worthwhile mentioning the special character of the manpower item of costs. First of all, it must be remembered that manpower costs must include not only salaries, but also social benefits, insurance, medical treatment, transportation, etc. In many cases irrigation projects are found in out-of-the-way places, and they must also include housing facilities, schools, shops, etc. for the workers and their families. Secondly, different tasks require different types of workers — field and office workers, irrigators, machinery operators, mechanics, construction workers, and surveyors, etc. In many cases short preparation courses must be arranged for these workers and consultations with agronomists and irrigation engineers may be indicated. Thirdly, a good management and organization are necessary to keep workers efficient and happy. The costs mentioned above are, in part, a function of the amount of water (per hectare) required for irrigation. This depends, on one hand, on the optimal water requirement of the crop, and on the other hand, on climatic (temperature, precipitation) conditions. Another factor, which is more under our control, is the efficiency of irrigation with its various components. Irrigation Benefits While costs are more or less clearly enumerated and can be estimated quite fairly with the help of available data and personal experience, the matter of benefits is much more difficult. First, it is necessary to decide whose benefits are we taking into consideration: benefits to the operator, to owners, to sponsors of the projects, or benefits to the farmers in the region where the project is found, or benefits to the whole nation. These groups may have conflicting interests and sometimes the law has to settle this problem. Another difficulty is that many of the benefits do not have a clear market value. These are the "intangibles". As has already been mentioned, there are methods of quantifying such benefits and ascribing to them money values, but these methods are mostly subjective and different people will obtain different values for the same benefits. This may sometimes mean the difference between an economically justifiable and an unjustifiable project. It is therefore advisable that with projects with a great deal of "intangibles", the criterion of acceptance (B/C) ratio should be higher than customary. Thus, small changes in the estimate of this type of benefits will not have a decisive value in the analysis. Four types of benefits should be taken in consideration in irrigation projects. Direct Benefits The main objective of an irrigation system is of course, the production of a good agricultural crop or crops. Its direct benefits consist of the value of the crop — its full value under arid conditions (where no crop at all would have grown without irrigation), or its additional value, compared with "dry" growing, where some crop could have been obtained without irrigation. The value of the crop is its market value. It depends, of course, on the quantity harvested, but not only on that. Irrigation may have a marked effect on the unit value of the crop, mostly by improving its quality (size, shape, flavor, uniformity, etc.) or by providing out-of-season fresh fruit, vegetables, or flowers. Subsidies and government control of prices should, of course, be taken into account. Indirect Benefits Indirect benefits of irrigation systems are many. They range from physical benefits, such as increasing actual crop area by producing more than one crop per year on the same field or changing the atmospheric humidity in arid regions, to social and economic benefits, such as the raising of living standards in the area, improving employ-

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ment conditions, providing recreation facilities (in reservoirs and ponds), etc. In many cases an irrigation system acts also as a domestic water supply system, with positive and/or negative effects on personal convenience, hygiene, and health. These benefits, although indirect, are generally quantifiable and are easily included in the analysis. The problem is not to overlook them, but try and determine atfbenefits "to whomsoever they may accrue". Intangible Benefits These are more difficult to pinpoint and assess, but they are important, nevertheless. Usually some of the indirect benefits can also be included under this heading. Intangibles generally refer to benefits connected with economic independence and self-supply, with the irrigation project's effects as a development factor, with the development of arid regions, and so on. They also include effects on efficient utilization of manpower, capital, and other resources, and on making farming a more agreeable, profitable, or industrialized practice. Salvage Value This is not a benefit of the project, but it must be included, in the analysis, as a benefit. It is the market value of the project assets at the end of its economic life. This may include sale value of equipment and material, value of land and structures, etc. This is the only benefit which is not annual. In present worth calculations its value L is capitalized by multiplication by

If the analysis is made on an annual basis, we use

The factor (i/q" - 1) is called the sinking fund factor(S¥) and can be shown to be SF = CRF X q~n = CRF - i

All the above benefits are often expressed as benefits per unit of some resource, most commonly as benefits per hectare, per cubic meter of water, per unit of manpower, etc. (depending on the relative scarcity of the resource). This form assumes linearity of the function benefits = /(resource). This is generally not the case and marginal benefits should be used. It must also be remembered that all benefits are only estimates of probable future values which are not known in advance. The estimates are generally expected values (averages). If data are adequate, it may be possible and advisable to use the distribution of future benefits in the analysis, with "rewards" and "penalties" for extreme values. ALLOCATION OF COSTS When the financing of a system has to be divided among different groups (as is often the case with large irrigation projects), the question of allocation of costs must rise. This question seems fairly simple at first glance, but actually is quite complicated. Moreover, there is no single, uncontroversial answer. In most cases, a compromise between conflicting interests must be agreed upon according to certain guiding principles.

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First, all separable costs should be determined. These are the costs clearly attributable to a single group or party. These may be direct costs of a system element benefiting only this group or the difference between the cost of the whole project with and without this element. In most cases the sum of all separable costs will be smaller than the total cost of the system. The difference is the nonseparable cost, which is connected with the benefit of more than one group, or cannot be directly connected with any benefit. This type of cost must be divided among all those who benefit from the project. This should be determined preferably by using simple methods, since complicated methods do not add to the "correctness" of the allocation. The sum of all allocations should be equal to the total cost of the system. No allocation should exceed the benefit that the group derives from the project, or be less than the separable costs pertaining to that group. No allocation should exceed the cost of any possible alternative project which could provide the said group with the same benefits. Users having priorities with respect to the use of the project's output should get higher cost allocations. When the system is paid for by a central agency, such as the government or the U.N., it is still worthwhile to allocate costs, so that the economic efficiency of the system can be analyzed and brought to an optimum by excluding noneconomic subsystems. BEARING THE COST The economic analysis of an irrigation project may be calculated according to the procedures in Appendix A and carried to a high degree of sophistication with the use of computers. Proper evaluation of the significance of the results must, however, rest with the judgement of the planners and the higher-level decision makers, since it extends beyond the realm of pure economics and enters the fields of sociology and government. The problem, put in its simplest terms, is that very few irrigation projects can be proven to be 100% economically viable. While this is often true in the most advanced countries, it is almost incontrovertible in the developing countries of the third world. In many such countries, the history of irrigation development shows that the very profitable and economically sound projects were developed earlier, and often by private investment, with full advantage taken of the then prevailing low costs of land, labor, water, and other inputs. In these countries the government or other public bodies are latecomers in the development race. Consequently they have to contend with the more difficult sites, requiring greater investments in primary water source development, roads, infrastructure, land clearing, reclamation of saline areas, etc. The higher costs of land settlement are a public expense at a standard of living which, although modest today, would have been considered as unnecessarily luxurious for the rural populations of one or two generations ago. The cost of financing has also risen considerably in the past 30 or 40 years. Expressed, therefore, in simple economic terms of cost-benefit, or rate of return, a fair and true analysis would result in negative findings for a great many projects. The crux of the question is the following: how much of the true cost of an irrigation project should be borne by the resulting agricultural production? The urban taxpayer would naturally be inclined to answer: all of it. The farmer will say: as little as possible. The government planners, faced with this dilemma, must try to judge the degree of benefit which may accrue to the general public and to the "state" as a result of the project. It can be argued, for example, that although uneconomical in terms of the domestic

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currency, a project may result in an important saving in foreign currency, or even an earning of foreign currency through export of the produce. This is a benefit to the general public. The project may increase the self-sufficiency of the country for basic supplies of food and fiber. This may be of great importance to countries faced with the threat of economic or military hostilities. An extensive land-settlement program, based upon irrigated agriculture, may be an important component in the solution of urban problems such as relieving pressure of unemployment and overcrowding in slum areas. The irrigation of areas bordering on deserts may create an important barrier to the advance of desertification. These are but a few of the many reasons which may justify the distribution of the financial burden of creating an irrigation project upon the shoulders of many sectors of the population. Another approach is the following. Successful irrigated agricultural production may give rise to a whole chain of related economic activities which benefit a broad spectrum of the population. These include transportation, construction, food industries, processing plants for industrial crops, machinery manufacture and sales, feeds and fertilizers, professional services of all sorts, chemical and pharmaceutical industries, aerial spraying, etc. Since these secondary effects form ever-widening circles on the pond after the first stone has been dropped, there is no way of knowing where they end. In short, it can be decided that the stimulation of any economically productive activity such as agriculture has a generally beneficial effect upon the entire population, and as such it is justified to allow the costs to be covered from the general taxes. An intermediate approach may be as follows: the basic investments in water resource development and distribution and in land reclamation and settlement should be borne by the public, and the current operating costs of the system should be borne by the farmers. This approach is often narrowed down to the main question of the price of water. How is this price fixed in relation to the actual cost of the water? If the water is provided free of charge, this represents full subsidy of the farmer by the general public (through the government). If the price is set equal to the real cost, this means that the farmer must bear the entire burden, and the value of most produce will not support such an expense. The price of water must, therefore, be partially subsidized at a rate which will allow for profitable farming without excessive taxation of the urban sector. The determination of this golden mean for a given set of circumstances requires the wisdom and insight of a Solon. It is more usually determined by an equilibrium of political power between the various sectors, under a given configuration of the legislature in democratic regimes. Under less democratic regimes, a host of special factors may influence the policy maker, which are beyond the scope of the present study to consider. A word of warning must be expressed regarding the provision of free irrigation water to the farmers. However desirable this may be from a social point of view, it may cause serious hazards from a technological point of view. It has happened in many countries that the provision of plentiful irrigation water at very low rates, or free of charge, has resulted in excessive use of water. This has resulted in the rising of the water tables, water-logging, and subsequent salinization of the soil. Regardless of economic or social considerations, the farmer must in all cases be charged enough for the water to encourage him to measure the irrigation applications and to strive toward greater irrigation efficiencies and water economies for the good of both the plant and the soil. In summary, the foregoing comments regarding the inapplicability of simple economic analyses in decision making with respect to irrigation projects should not be construed as rendering useless all of the techniques presented in this chapter. Regardless of the factors affecting the final decisions, the economic analyses are highly important in comparing alternative projects so that the high-level decisions can be based

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upon objective evaluations. The "state" may be willing to pay more than a project appears to be worth. It is, however, entitled to know exactly how much the subsidy amounts to in every case. APPENDIX A TIME-STREAM CALCULATIONS OF ECONOMIC VALUES Introduction Costs and benefits of an economic system usually spread over a prolonged time period. Costs are incurred both in a concentrated form, mostly at the start of the project, during the installation stages, and as annual OMR and other types of expenditures. Most benefits are spread over the project's productive period. Comparison of benefits and costs must use a single common type of these values, either expressing all annual values in terms of their present worth, or else expressing the concentrated costs as annual values (such as payments on a loan). These methods will be seen to be equivalent and choice between them will be made according to convenience or local custom. Compound Interest and Capitalization The relationship between a sum P today and a sum F in the future, say n years hence, is computed on the basis of compound interest. A sum P invested now at an interest rate of 100i% paid annually, will be worth after n years F = P(l + i)n = Pqn

where q = 1 + i. Conversely, a sum F n years hence is at present worth only

The present-worth value of a stream of payments (costs or benefits) paid from now during the next n years at an interest rate of 100i% paid annually is calculated in a similar manner

When all payments F( are equal ( = F), then:

The expression in parentheses is the sum of a geometrical progression with n terms, where the first term and the common ratio are both equal to 1/q. The sum of such a progression is equal to

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The value (1 - q~")/i = (q" - l)/iq" is called the present worth factor (PWF) or the capitalization factor; it is, as can be observed, a function of i and n. Expressing a present value as a sum of n equals annual payments is done in the same way, by computing the annual payment F:

The value i/(l — q~") = iq"/(q" — 1) is termed capital recovery factor (CRF). Both of these factors have been computed for many values of i and n and are presented in convenient tables in most engineering and economics handbooks (see Table 1). When only one table is available, it is easily transformed by PWF x CRF = 1 for each i and n. Use of these tables facilitates greatly the calculations required for benefit-cost evaluations. Example 1 Suppose an irrigation project costs $100,000 for design and installation (expenses incurred on day of completion), with annual costs of $5000. After 10 years, a pumping plant is to be added costing $20,000. At the end of 25 years, the system is to be dismantled, and parts of it will be sold at an estimated "salvage value" of $10,000. The expected annual benefits are $25,000. Calculate the B/C ratio at an interest rate of 10%, compounded annually. Solution: comparing present worth values; Present worth of: initial investment Annual costs: 5000 xpWF(0.10,25) = 5000x9.077 Pumping plant: 20,000 x ( i + 0.10)-10 = 20,000x0.386 Total costs (present value) Present worth of benefits: 25,000 x PWF (0.10, 25) = 25,000x9.077 = Salvage value: 10,000 x(l + 0.10)-25 = 10,000x0.092 = Total benefits (present value)

$100,000 45,385 7,720 $153,105 226,925 920 $227,845

B/C ratio = 227,845/153,105 = 1.49 Example 2 A sprinkling irrigation system costs $10,000 for design and installation (excluding sprinklers and portable pipes). The system is supposed to last about 40 years. Sprinklers and pipes have to be replaced after an average of 10 years, at a cost of $800 for each replacement. Annual OMR costs are $300 and expected annual benefits are $2000. Calculate total B and C and B/C ratio, in annual terms, at 6% interest rate.

Table 1 1/CRF = PWF = q" - 1/iq" = 1/i (1 - q-") PRESENT VALUE OF $1 RECEIVED ANNUALLY Periods to be paid

1%

2%

4%

6%

8%

10%

12%

14%

15% 16% 18%

20%

22%

24%

25%

26%

28%

30%

35% 40% 45% 50%

1 2 3 4 5

0.990 1.970 2.941 3.902 4.853

0.980 1.942 2.884 3.808 4.713

0.962 1.886 2.775 3.630 4.452

0.943 1.833 2.673 3.465 4.212

0.926 1.783 2.577 3.312 3.993

0.909 1.736 2.487 3.170 3.791

0.893 1.690 2.402 3.037 3.605

0.877 1.647 2.322 2.914 3.433

0.870 0.862 1.6261.605 2.283 2.246 2.8552.798 3.3523.274

0.847 1.566 2.174 2.690 3.127

0.833 1.528 2.106 2.589 2.991

0.820 1.492 2.042 2.494 2.864

0.806 1.457 1.981 2.404 2.745

0.800 1.440 1.952 2.362 2.689

0.794 1.424 1.923 2.320 2.635

0.781 1.392 1.868 2.241 2.532

0.7690 .741 1.361 1 .289 1.816 1 .696 2.166 1 .997 2.436 2 .220

0.7140..690 0.667 1.224 1,.165 1 . 1 1 1 1.589 1 .493 1.407 1.849 1.720 1.605 2.035 1,.876 1.737

6 7 8 9 10

5.795 6.728 7.652 8.566 9.471

5.601 6.472 7.325 8.162 8.983

5.242 4.917 6.002 5.582 6.733 6.210 7.435 6.802 8 . 1 1 1 7.360

4.623 5.206 5.747 6.247 6.710

4.355 4.868 5.335 5.759 6.145

4.111 4.564 4.968 5.328 5.650

3.889 4.288 4.639 4.946 5.216

3.7843.685 4.1604.039 4.4874.344 4.7724.607 5.0194.833

3.498 3.812 4.078 4.303 4.494

3.326 3.605 3.837 4.031 4.192

3.167 3.416 3.619 3.786 3.923

3.020 3.242 3.421 3.566 3.682

2.951 3.161 3.329 3.463 3.571

2.885 3.083 3.241 3.366 3.465

2.759 2.937 3.076 3.184 3.269

2.643 2.802 2.925 3.019 3.092

2 .385 2 .508 2 .598 2 .665 2 .715

2.168 I .983 1.824 2.263 2,.057 1.883 2.331 2,.108 1.922 2.379 2,.144 1.948 2.4192,.168 1.965 2.438 2.456 2.468 2.477 2.484

11 12 13 14 15

10.368 9.787 8.760 11.25510.575 9.385 12.13411.343 9.986 13.00412.10610.563 13.86512.84911.118

7.887 8.384 8.853 9.295 9.712

7.139 7.536 7.904 8.244 8.559

6.495 6.814 7.103 7.367 7.606

5.937 6.194 6.424 6.628 6.811

5.453 5.660 5.842 6.002 6.142

5.2345.029 5.4215.197 5.5835.342 5.7245.468 5.8475.575

4.656 4.793 4.910 5.008 5.092

4.327 4.439 4.533 4.611 4.675

4.035 4.127 4.203 4.265 4.315

3.776 3.851 3.912 3.962 4.001

3.656 3.725 3.780 3.824 3.859

3.544 3.606 3.656 3.695 3.726

3.335 3.387 3.427 3.459 3.483

3.147 3.190 3.223 3.249 3.268

2 .752 2 .779 2 .799 2 .814 2 .825

2..185 1.977 2..196 1.985 2,.204 1.990 2..210 1.993 2..214 1.995

16 17 18 19 20

14.71813.57811.65210.106 15.56214.29212.16610.477 16.39814.99212.65910.828 17.22615.67813.13411.158 18.04616.35113.59011.470

8.851 9.122 9.372 9.604 9.818

7.824 8.022 8.201 8.365 8.514

6.974 7.120 7.250 7.366 7.469

6.265 6.373 6.467 6.550 6.623

5.9545.669 6.0475.749 6.1285.818 6.1985.877 6.2595.929

5.162 5.222 5.273 5.316 5.353

4.730 4.775 4.812 4.844 4.870

4.357 4.391 4.419 4.442 4.460

4.033 4.059 4.080 4.097 4.110

3.887 3.910 3.928 3.942 3.954

3.751 3.771 3.786 3.799 3.808

3.503 3.518 3.529 3.539 3.546

3.283 3.295 3.304 3.311 3.316

2 .834 2 .840 2 .844 2 .848

21 22 23 24 25

18.85717.01114.02911.76410.017 19.66017.65814.45112.04210.201 20.45618.29214.85712.20310.371 21.24318.91415.24712.55010.529 22.02319.52315.62212.78310.675

8.649 8.772 8.883 8.985 9.077

7.562 7.645 7.718 7.784 7.843

6.687 6.743 6.792 6.835 6.873

6.3125.973 6.3596.011 6.3996.044 6.4346.073 6.4646.097

5.384 5.410 5.432 5.451 5.467

4.891 4.909 4.925 4.937 4.948

4.476 4.488 4.499 4.507 4.514

4.121 4.130 4.137 4.143 4.147

3.963 3.970 3.976 3.981 3.985

3.816 3.822 3.827 3.831 3.834

3.551 3.556 3.559 3.562 3.564

3.320 3.323 3.325 3.327 3.329

2 .852 2.498 2,.221 2.000 2 .853 2.498 2,.222 2.000 2 .854 2.499 2..222 2.000

2.489 2.216 1.997 2.492 2 .218 1.998 2.494 2 .219 1.999 2.496 2..220 1.999 2.850 2.497 2,.221 1.999

2.855 2.499 2..222 2.000 2 .856 2.499 2 .222 2.000

26 27 28 29 30

22.79520.121 15.98313.003 10.810 23.56020.70716.33013.211 10.935 24.31621.281 16.66313.40611.051 25.06621.84416.98413.591 11.158 26.80822.39617.29213.765 11.258

40

32.83527.355 19.793 15.046 11.925 9.779 8.244 7.105 6.642 6.234 5.548 4.997 4.544 4.166 3.999 3.846 3.571 3.333 2.857 2.500 2.222 2.000

50

39. 196 3 1 .424 21 .482 15.762 12.234 9.915 8.304 7.133 6.661 6.246 5.554 4.999 4.545 4.167 4.000 3.846 3.571 3.333 2.857 2.500 2.222 2.000

9.161 9.237 9.307 9.370 9.427

7.896 7.943 7.984 8.022 8.055

6.906 6.935 6.961 6.983 7.003

6.491 6.118 6.514 6.136 6.5346.152 6.551 6.166 6.5666.177

5.480 5.492 5.502 5.510 5.517

4.956 4.964 4.970 4.975 4.979

4.520 4.524 4.528 4.531 4.534

4,151 4.154 4.157 4.159 4.160

3.988 3.990 3.992 3.994 3.995

3.837 3.839 3.840 3.841 3.842

Note: CRF = capital recovery factor; PWF = present worth factor; q = I + i; i = interest rate; n = number of years.

3.566 3.567 3.568 3.569 3.569

3.330 3.331 3.331 3.332 3.332

2.856 2.500 2.856 2.500 2.857 2.500 2.857 2.500 2.857 2.500

2.222 2.222 2.222 2.222 2.222

2.000 2.000 2.000 2.000 2.000

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Solution — Since the economic life of the sprinklers and pipes is much shorter than that of the rest of the system, they are not included in the total installation costs, but their costs are supposed to be equally spread over the whole period, as a component of the **R" ( = replacement) element of the OMR costs. This spreading can be done using the following equation: A = P [CRF (i, n') - CRF (i, n)]

where

A = ami ua7 replacement cost for replaced elements P = replacement costs for each replacement n' = economic life of replaced elements n = economic life of the system

Thus, computing annual values: Initial investment: 10,000 x CRF (6, 40) - 10,000x0.0665 = Annual operation and maintenance costs = Replacement costs 800 [CRF (6, 10)-CRF (6, 40)] = 800(0.1359-0.0665) = 800x0.0694 = Total annual costs Annual benefit

$ 665 300 55 $1020 $2000

B/C ratio - 2000/1020 = 1.96 A simpler way of spreading costs is by dividing the replacement costs over the replaced elements' life: Initial investment - annual value = Annual OMR costs: 300 + 800/10

Total annual costs = Annual benefits =

$ 665 380

$1045 $2000

B/C ratio = 2000/1045 = 1.91 Estimated Lives of Irrigation Systems Elements The two factors used in the calculations above are functions of the interest rate and of the economic life of the system. The term "economic life" means the average duration the system is expected to be in operation before it will have to be replaced due to failure, obsolescence, or other reasons (such as changes in land use, etc.). Often economic life is taken as equal to the duration of payments on the loan taken for the initial costs. Table 2 presents values of economic lives of some elements of water and irrigation systems. Most systems consist of elements having different economic lives. In such cases, each element should be treated separately, or (as was shown in the second example of the preceeding paragraph) the life of the system can be considered as that of its longestlived elements, while the cost of shorter-lived items will be treated as part of the annual OMR costs.

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Table 2 ECONOMIC LIVES OF SELECTED IRRIGATION SYSTEM ELEMENTS In years Dams Wells Ponds and reservoirs Pumps Motors Canals and ditches Pipes Steel Concrete and asbestos-cement Aluminium (portable) Plastic (underground) Hydrants Water meters Sprinklers Mechanically moving sprinkling systems Fittings of portable pipes

50—150 25—50 20—50 20—25 10—20 25—50 20—40 20—40 15 20—40 20—40 20 5—10 10—15 15

Selection of Interest Rate The selection of the proper interest rate for capitalization calculations often poses a much more difficult problem. This selection may sometimes be the decisive factor in determining whether a project is found to be economically justifiable or not. For example, a system with an initial investment of $100,000, an economic life of 50 years, and expected annual benefits of $7500 will be considered economically justified when capitalization is calculated at a 4% interest rate (present worth of benefits = $161,115), while at 8% (present worth of benefits = $91,755) it will be turned down. In the open market conditions that generally apply to private enterprises, interest rates to be used are those that would have to be paid on bank loans required for financing the project. These interest rates are generally high — 10% and more. Irrigation systems, in most cases, are public projects, or at least publicly financed or subsidized. In such cases the public is, in a way, guaranteeing the money and therefore the money is supplied to such systems much more cheaply, i.e., at a much lower interest rate (4%, 6% etc.) These values are, of course, lower than the actual social cost of the money (which is what the money is worth to the public). In such cases it is sometimes suggested that the economic justification criterion is made more stringent (such as B/C > 1.5 or even B/C ^ 2, instead of B/C > 1). Use of the low values of i causes the preference of projects with high initial investments and low annual costs. Large initial investments with high interest rates result in excessive annual costs, thus lowering the B/C ratio.

REFERENCES Carruthers, I. and Clark, C., The Economics of Irrigation, Liverpool University Press, Liverpool, U.K., 1981.

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AUTOMATED COMPUTERIZED IRRIGATION Gideon Peri INTRODUCTION Automated computerized irrigation is a relatively new concept that emerged recently from the increased demand for better irrigation. The need for higher production in agriculture and the restrictions on availability of water quantities are the main reasons behind the need for better controlled and automatic irrigation. Studies of plant growth have shown that optimal yields are not necessarily a result of greater water quantities but of proper application scheduling (correct intervals and quantities). With the sophisticated irrigation systems and the associated accessories (fertilizer injectors, filters, pressure valves, etc.), control and automation is a required procedure for proper operation and management. A modern pressure system of irrigation consists of a pipe network branching out from the main source to the fields. At strategic nodes of the network there are valves which control the flow of water through the nodes. By selectively opening the valves, water can be routed to irrigate specific areas of the field. Water gauges placed at strategic points in the network are used to monitor the quantity and flow-rate of water passing these points. Due to limited water pressure and flow from the main source, all areas of a large field cannot be irrigated simultaneously. A farmer sets up a schedule of valves to be opened, one after another, either based on the amount of water to be passed by each valve or on time consideration. Usually, there are several queues of such valves with one valve open in each queue. Additional factors may be considered in the opening or closing of a valve. These may include: water pressure in the lines, wind and temperature conditions, soil moisture, and status of other valves or pumps. With ordinary irrigation systems, the achievement of a satisfactory irrigation performance (which can be defined as the uniform application of the required water depth in an economical way) is problematic due to many factors which affect the flow of water and its distribution after leaving the piping system. It is well known and accepted that the two basic assumptions which are applied in the design and operation of irrigation systems are not true. These are (1) the flow rates at various sections and outlets are known and (2) the flow rates at various sections and outlets are constant. These assumptions are not true in practice due to many factors like pressure dstribution, change in emitter sizes, clogging of filters, changes in pipe characteristics, topography, and others. Control and automation helps to reduce the effect of such factors towards better irrigation performance. With computerized automation a wide range of control is possible. Computerized irrigation has revolutionized agriculture. It has transformed what was a labor-intensive task into a science, possessing all the attributes of precision. No longer is irrigation left to the whims of nature or the capacity of labor. Detailed examination of water needs and the electronic processing of data have been combined to ensure that water is utilized to the maximum benefit and labor dependence is reduced to a minimum. The computer-based systems control all vital irrigation functions on a real-time basis. Water quantity, flow rate, water pressure, and environmental conditions such as wind speed, air temperature, soil humidity, rainfall, etc. are continually monitored before, during, and after every irrigation cycle. Control of insecticide and fertilizer injection, water flow rate, and the correction of malfunctions are carried out automatically. This 24-hr monitoring ensures that irrigation is performed at optimum efficiency.

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DESCRIPTION OF COMPUTERIZED CONTROL SYSTEMS A computerized automation control (CAC) for irrigation systems is a device which can activate various types of elements in an irrigation water system (valves, pumps, injectors) according to a program which has been fed to it previously. The computerized automation control varies over a wide range of different types. These can be described and characterized on the basis of one or a combination of the following factors. Extent and Size of the Irrigation Network that is Controlled by the CAC The CAC can be suited to control a minimal irrigation network composed of only one control head when the control head includes only the elementary components such as a valve and a water meter. On the other hand, comprehensive irrigation systems composed of several networks linked together, several pumping stations, various water sources, reservoirs, water tanks, etc. can be controlled by a CAC. Structure of the CAC There are four typical structures (Figure 1). Independent Field Unit (IFU) This includes a unit which is installed in the field and performs all the control functions. It includes a panel by which the irrigation program is inserted into the unit and the electronics which can accept the program and perform it. Other functions may include a display of the program or past events. The unit is installed in the field close to the water system. Control Center with Field Units (CCFU) The CCFU includes three major components: a control center in which irrigation programs are inserted, analysis, processing, and display of information from the field and print-out of events. The control center may include various components like computer, tape recorder, CRT, printer, communication equipment, map of network, etc. The field units contain the electronics to receive commands from the control unit and activate the solenoids or relays which are attached to them. The field units also receive the feedback from various meters, gauges, and sensors and deliver it to the control center. The communication link is an electrical cable through which information is transmitted from the control center to field units and vice versa. The communication cable can carry the power for operating the field unit. Control Center with Terminals (CCT) Any number of field units can be linked to a terminal. The terminal provides for inserting the irrigation programs and displaying or printing the present and past irrigation events. However, the information processing is carried out at a central unit which is linked to all the terminals. The control center is common to several terminals where each terminal handles the programing for the field units attached to it. Hierarchical Central Unit (HCU) In this type of electronic automation control, several control centers which are able to perform independently are also subjected to overall control by a priority control center which may grant priorities for several functions and may also command the control center below it. This type of EAC is similar to the CCT with the additional feature that the terminals can also carry out data and information processing and they can perform independently.

r

IGURE 1. Typical structures of computerized automation control. (1) Independent field unit; (2) control center with ield units; (3) control center with terminals; (4) hierarchial central unit.

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FIGURE 2,

Typical solenoid valve.

Typical Components and Accessories of Computerized Automation Control System A computerized automation control center includes all or part of the following. Central Unit The central unit includes a computer or microprocessor for data handling and processing, a keyboard panel to insert irrigation programs and to communicate with the computer, a display, a printer, and a tape to store all irrigation events. Field Unit The field unit is linked by a communication cable or radio to the central unit. It delivers the commands from the central unit to the accessories of the irrigation system (valves, pumps, injectors) and delivers the feedback from the field (water meter, anemometers, pressure gauges, etc.) to the central unit. Water System Control Accessories The water system control accessories include hydraulic or electrical valves, solenoids, water meters, filters, fertilizers, injectors, pumps, and boosters. These are commanded hydraulically through command tubes or electrically through electrical cables. A typical solenoid valve is shown in Figure 2.

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Sensors With computerized automated control, various sensors can be used to provide the system with direct information from the field. Sensors that are used with CAC are tensiometers, radiation gauges, evaporation pans, thermometers, humidity meters, etc. The sensors can provide an on-off contact or continuous readings.

CONTROL FUNCTIONS PERFORMED BY THE CAC The CAC can perform numerous control functions to ensure proper irrigation and efficient irrigation management. The various functions can be classified into several major groups. 1. 2. 3. 4. 5. 6.

Operation of irrigation programs according to preprogrammed instructions; the size of the program and flexibility of instructions may vary widely between various CAC units Measurement and monitoring irrigation network information such as flows and pressures and environmental data such as temperature, wind speed, soil tension, etc. in order to record, process, and respond to the data Operation of irrigation programs and network control on a conditional basis; the occurance of the condition is measured directly by the CAC Display of past and present events and information related to the irrigation; display can be in a form of synoptic map, CRT, printouts, etc. Operation of programs for special activities associated with irrigation; for example, backflushing of filters, conditional operation of pumps and boosters, pulse irrigation, emergency programs On-line execution of scientific programming associated with the irrigation operation; for example, scheduling programs and water network solving

In particular, the CAC can perform various activities which otherwise are impractical or inefficient. Most common activities, for example, are water dose on a quantity basis; sensing of high flow as indication of a burst pipe and low flow as indication for clogging or pressure drop; application of fertilizers on a time or quantity basis or in a proportion manner; providing pre- and post-fertilization flushing; direct response to wind and prssure; selection of pumps to be operated according to flow and pressure requirement; report of all irrigation events including failures, on-line and real-time response to sensors. ECONOMIC FEASIBILITY AND BENEFITS OF AUTOMATION IN IRRIGATION A computer-controlled irrigation system enables the precise management of an irrigation network by the constant surveillance and monitoring of all factors affecting irrigation. In this way, a variety of savings can be made including more efficient use of existing water resources, savings of water due to immediate detection and automatic isolation of bursts and leaks, better utilization of manpower, and increased crop yields due to timed irrigation and fertilization, all of which result in increased profitability. Following the introduction of CAC, several studies of the economic feasibility of computer-based irrigation have been carried out by the author and others. The results of these studies, based on a large number of systems already operating, reveal an average saving of water of 10 to 30% and 15 to 35% saving of energy, as compared with areas irrigated semiautomatically. Also found was a 5 to 10% saving in man-hours (in areas of 500 to 1250 acres) and an increase in crop yields by as much as 5%. The following are the most significant advantages of automatic irrigation as compared to any semiautomatic system.

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Savings in Water The saving of water during irrigation can be realized in terms of the prevention of water waste and the more efficient use of existing water sources. The following factors contribute to the wastage of water. Rationing Errors Rationing on a time basis — When rationing water according to time, the volume of water reaching any given area is a function of the irrigation time, assuming that the pipeline pressure is always known. In a semiautomatic system, strict time control requires that the operator be at the pipe control at the exact time, day or night, in order to open or close it. Rationing on a Volume Basis This includes the following factors: 1. 2. 3. 4.

Error of the machinery: it was found that there can be deviations of approximately 1.5%, inherent in the equipment itself Inaccuracies in the scales of the equipment Operator's errors when programming the required quantity Nonclosure of the equipment due to faulty timer

In comparison, in a computer-based system, rationing inaccuracies, in the worst case, are in the order of only 1%. Cases of not closing on time account for about 1% of all closures. However, a malfunction such as nonclosure on time will be discovered by the system and it will close the main line automatically. Wind Speed Variations The volume of water lost is measured as a percentage of the ration and as a function of the "windy hours" during irrigation. After studying the traits of winds in Israel, the research revealed that water loss is divided approximately as follows: • • •

In irrigation before noon, 6:00 to 12:00, approximately 10.3% water loss In irrigation after noon, 12:00 to 18:00, approximately 18% water loss In irrigation at night, 18:00 to 06:00, approximately 5% water loss

The conclusion is, clearly, that it is most efficient to irrigate at night and to stop irrigation during the hours when the wind is strongest. Pipeline Pressure Variation Sprinkler manufacturers recommend pressure conditions also be met in order to ensure uniform water distribution. Reducing or raising the pipeline pressure during irrigation causes the area near the sprinkler to receive too much or too little water, even though the correct total volume of water is utilized. Therefore, a process for measuring the lost water quantities has been developed. This is based on the customers' data regarding the average time during irrigation, when the pressure is reduced. The water loss may reach 30% and more if the pressure is reduced by 10 m (1 atm). The automatic irrigation system identifies reduction in pressure and closes water pipes or operates additional boosters, whichever may be needed. Pipeline Drainage The automatic irrigation system enables the closure of the secondary valves. In these cases, the main line remains full of water and its drainage is prevented.

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A program which takes into account the length of the pipelines, their slopes and the number of openings and closings has been developed, and according to this data, the quantity of water saved may be calculated. Malfunctions or Breaks The automatic computerized irrigation system, in contrast to other irrigation methods, is able to detect a higher than desired flow and to close valves accordingly. This enables saving the water which would otherwise have been wasted because of pipeline breaks (especially in aluminum pipelines). Damage to the ground and the erosion of seeds, by overwatering, is prevented. The calculation of the water saved is static. It is based on the customer's definition of the leakage percentage occurring during a standard irrigation period. Breaks of a larger nature, although occurring less frequently, are taken into account. This is because the computerized system has the ability to cope with these, by being able to protect the main lines. In conclusion, the automatic computerized irrigation system allows the user to save water lost due to the following factors: 1. 2. 3. 4. 5.

Rationing accuracy Wind speed variations Pipeline pressure variations Pipeline drainage System malfunctions and breaks

Savings in Energy Savings in energy are achieved by the following: 1. 2. 3. 4.

Saving of water Booster and pump operation depending on the system requirements (pressures and flows) and not their indiscriminate operation Night-time irrigation using low-cost energy Substantial reduction in the number of trips to the field (resulting in savings of fuel)

Studies have shown that the saving of energy is approximately 5% greater than the saving of water. Savings in Labor Hours General The saving of labor hours in irrigation can be realized in terms of activities performed by the automatic system which previously were not. The general list of activities include: 1. 2. 3. 4. 5.

Opening and closing of valves Control before irrigation Control and administration Installation of the irrigation equipment in the field Continuous checking and maintenance of the equipment and pumping stations

With large installations the traveling time was taken in account, i.e., the time saved by not traveling to and from the field. Nonrelated field activities requiring separate journeys to the fields were not taken into account. It was found that the main areas in which it is possible to save labor are in 1, 2, and 3 above.

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Calculation A factor K which expresses the portion of labor saved was determined for the savings in labor hours, according to the agricultural environment and its specific problems. Experience in Israel shows that the average value for this factor is 1. 2. 3.

K ~ 0.9 for opening and closing valves K = 0.3 for checking before the irrigation is begun K = 0.5 for control and administration

(For the other activities, K is much smaller). Another important factor which is difficult to evaluate in time is the reduction in the number of people involved in irrigation work. It must be remembered that many irrigation activities are done at unusual hours in the evening, at night, in the early morning, or in bad weather. Increase in Crop Yield Data concerning several large installations has shown that an additional yield of 3 to 5% is possible due to efficient irrigation. The following points should be considered when evaluating the benefits of a computer-controlled irrigation system with respect to crop yield. Uniformity of Distribution Pressure and Wind Control Control of external factors such as wind and pressure can lead to an increase in crop yield as demonstrated by the following calculation: The influence of the wind, in season, ranges from 10 to 20 Christiansen units per 0.1 ha (quarter acre). On an experimental basis, it was found that an increase in wind velocity of 1 m/sec causes a reduction in the uniformity of distribution of 10 Christiansen units. The value of ten such units with respect to cotton crop yield is 100 kg cotton per acre. Therefore, if 2000 to 2400 kg cotton per acre is taken as an average, the additional crop yield as a result of wind control is approximately 5%. A similar calculation may be made for the effect of pressure drop on the uniformity of dispersion. Accuracy of Application Application accuracy is a function of two factors: (1) accuracy of the water quantity used and (2) accuracy in the timing of irrigation. By means of automation, it is possible to precisely measure and control these factors. It is clear that there are stages in the growth of crops when it is critical to control the timing and quantity of irrigation. An error in either timing or quantity may result in great damage. In an automatic irrigation system the quantities and timing are accurately controlled by a computer. In Nebraska (U.S.), an estimate was made of the benefits gained by accurate rationing and timing. A computer was used and the survey was conducted throughout the entire state. The benefit to a crop of maize with accurate quantities and timing was $35.00/acre (in 1967). Application of Fertilizers and Herbicides through Irrigation In both cases, precise timing is most important because of the high cost of materials and the need for pipeline cleaning before and after chemical injection. An automatic irrigation system is capable of carrying out all the required activities with the greatest precision and with an important saving in manpower. It is almost impossible to carry out an exact fertilization without having full automation.

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The economic value is expressed by the following factors: 1. 2. 3. 4. 5. 6.

Correct rationing of the quantity of the material Injection of the material at the correct times Cleaning of the pipeline before and after injection Cleaning of the plants, if required Economy in manpower Reduction of the waste of expensive fertilizers

Control over all of the aforementioned factors can lead to additional crop yield and/ or a significant reduction in the production cost. Exploitation of Water Sources This factor is not directly included in additional crop yield but, by using automation, it is possible to exploit water sources more effectively. This may include 24 hr a day irrigation, or switching to more inexpensive water sources if 24-hr operation is not possible with existing resources. To save energy, the filling of reservoirs may be programed to take place during off-peak electricity hours. The final savings will be expressed in large sums of money and in the reduction of the facilities needed for irrigation. Expanding Control over Irrigation Systems The CAC features real-time evaluation of all irrigation activities in the field. It also evaluates all vital irrigation information such as wind speed, air temperature, humidity, etc. The system computes and reports to the user, the quantities of water passing through each pipeline. It also accumulates and reports daily, weekly, and seasonal totals. A map of the field presents the overall situation at a glance; lines operating, pumping stations operating, breakdowns, etc. The operator may request the computer to print out, at any time, lines in operation and the quantity of water which has flowed through them. It is difficult to assess the monetary value of these factors, but it is clearly substantial.

GENERAL DESCRIPTION OF MOTOROLA ISRAEL SYSTEM The Motorola Israel CAC can be taken as a typical example of a computerized automation control in irrigation. The MIR® 1080 The irrigation control systems developed by Motorola Israel allow the operator to control irrigation networks from central locations. In the large system, the MIR® 1080, the central site is a control room, housing the computer and related hardware, which is connected to satellite units situated in the fields. The computer holds such information as the preset limits for operation, i.e., the quantity of water per plot, pressure limits, flow-rate limits, wind speed, air temperature, and soil humidity limits. The computer receives real-time measurements of the above vital information from transducers in the field, compares these with the desired limits, and modifies the irrigation cycle accordingly. The computer issues commands for the operation of water valves, boosters, injection of fertilizers, etc. according to the irrigation program or as an emergency measure due to some abnormality detected by the sensors. If a leak or burst occurs, the computer orders the closure of the water supply to the area in question, preventing damage and saving water. In the event of

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high wind or heavy rain, irrigation is stopped. In extreme heat or frost, irrigation is started. In a similar manner, the computer is programed to deal with all anomalous circumstances. At the same time, the computer stores in its memory when, where, and what happened and, in the case of the MIR® 1080, produces a hard copy printout on the teletype terminal. In the event of water rationing, the best crop with the best profit potential can receive optimum irrigation by setting up the appropriate sequential order for opening the valves. In its memory, the computer holds daily, weekly, and seasonal data which may be used by the farmer to aid in the planning of future irrigation and fertilization. The interface between the computer and the operator facilitates the easy entry of data by using a conversational mode of communication based on simple instructions. Thus, the operation of the system does not require the expertise of a computer technologist. The computerized irrigation control systems may be installed and managed with relative ease. Control sequences are simple enough to be mastered with minimum training, and maintenance is made simple by the use of replaceable printed circuit cards. The user can effectively handle the large system after a few weeks of training. The Matarol® 2000 The Matarol® 2000 is Motorola Israel's answer to the need for computerized irrigation of small areas of land. The unit is equally suitable for the open field, the greenhouse, or the nursery and is ideal for groves, orchards, vineyards, plantations, and vegetable plots. The Matarol® 2000 is a by-product of the MIR® 1080 and offers the same facilities and functions as the large system. In this case, the control center and the satellite (field unit) form one piece of equipment which is situated in the field. The Matarol® is able to control between 2 and 18 valves, boosters, and pumps, in addition to the main valve and the fertilizer pump. It receives data from water meters, fertilizer meters, pressostats, thermometers, tensiometers, etc. as required and analyzes the data in order to execute irrigation programs at optimum efficiency. The Matarol® is hermetically sealed against bad weather and dust and runs off a dry battery, making it completely independent of external power sources. The unit provides computerized control of irrigation networks over areas of 0.25 to 250 acres (0.1 to 100 ha). A typical scheme of an irrigation network under the control of the Matarol® is shown in Figure 3. The following is a sample of the capability of the Matarol® 2000: • •

•

•

There is unlimited sequential irrigation in any valve order, controlled by either quantity and/or time or flow With excessive flow (burst pipe) or insufficient flow (blocked filter or sprinkler), the equipment automatically closes the valve in question, opens the next one in line, and generates an alarm signal. The computer also commits to memory the place of the burst or stoppage and the quantity of water which flowed through the line. This information is retrievable by the operator at a future date. The unit pays special attention to the subject of fertilization. It is known that the quantity and timing of fertilization is of the utmost importance to crop growth. The Matarol® 2000 enables injection of fertilizers to an accuracy of four digits. The fertilization cycle includes prewatering to ensure uniform dispersion and the rinsing of the irrigation lines before stopping the cycle. The computer accumulates the quantities of water and fertilizers given to each plot even though only one water meter is installed in the main supply. The accumulated quantity is very important for day-to-day follow-ups and also for longterm investigations and planning of quantities to be supplied to a plot.

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FIGURE 3. Typical scheme of automated irrigation with the Matarol® system.

•

• •

• •

Water pressure, wind speed, air temperature, and the moisture content of the soil are all measured by the computer to optimize irrigation and fertilization. For example, if the tensiometer informs the computer that no irrigation is required, water will be saved and over-watering prevented. In the case of a pressure drop, the computer will stop the irrigation and only start it again when the pressure rises to a level determined by the farmer. In a similar fashion, the computer controls irrigation during abnormal wind and temperature conditions. The Matarol® 2000 stores emergency programs to deal with exceptional circumstances, e.g., if exceptionally high temperatures are experienced inside a hot house, the computer will activate the cooling sprinklers. During an alarm situation or a malfunction, the Matrol® 2000 will indicate what has happened, when it happened, and what occurrence took place (e.g., abnormal flow, weak battery, pressure drop, valve nonfunction, etc.). This alarm condition may also be relayed to the operator via a paging system. The equipment may be programed for an entire week with an unlimited number of cycles per day. The weekly program is repeated week after week automatically. However, at any time changes may be made in the program. Like the new digital watches, the easily read alphanumeric display informs the farmer of what is taking place in the controlled area. Also, on interrogation, it will inform him of all events which occurred when he wasn't present.

The Matarol® 2000 is a smart and efficient robot. However, what happens if by chance it stops functioning? — a very small chance indeed. In this eventuality, small, manual three-way valves, situated next to the equipment, may be operated.

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Operation The Matarol® 2000 is operated in a similar fashion to a pocket calculator. The keyboard and associated alphanumeric display enable easy operation which can be learned within an hour. The user must enter irrigation information into two data tables in addition to setting up the real-time clock on which the Matarol® operates. The operator also receives real-time information about events occurring in the network via a third data table. Preset Data Table In this table there are up to 18 inherent schedules into which data may be entered. A schedule number must be selected after which data must be entered under the following headings: • • • • • • • • • •

VALVE: the number of the valve(s)(l to 18) WATER: the quantity of water (m3) FLOW: the nominal flow rate (mVhr) PERT: the quantity of fertilizer (liters) PREWATERING: the quantity of water for irrigation before fertilization starts IRRIGATION DAY: the day(s) on which the program operate(s) START: the start time of the irrigation program (hour) STOP: the stop time of the irrigation program (hour) TOTAL START: the number of irrigation cycles WAITING: the waiting interval between cycles (hour)

Current Data Table This table indicates events that are occurring or have occurred in the field. The data displayed comes under the following headings: • • • • • • • • • •

SCHEDULE: the number of the schedule STATUS: the status of the irrigation program WATER: the remaining water quantity for irrigation in the schedule (m3) FLOW: the actual flow rate (mVhr) FERT: the remaining quantity of fertilizer for injection with the water in the schedule (liters) TOTAL WATER: the accumulated water quantity already used for irrigation in the schedule TOTAL FERT: the accumulated fertilizr quantity already used for fertilization in the schedule TOTAL START: the remaining number of irrigation cycles START: the start time of the next cycle VALVE: the number of the valve or valves in the schedule Under the heading "STATUS" there are eight possible conditions:

• • • • •

IN PROGRAM: indicates that the schedule is programed to take place on that day WATERING: indicates that the schedule is actually irrigating at that time FINISH: indicates that the schedule has finished all its cycles for that day WAITING: indicates that the schedule is waiting because of information received from a transducer,e.g., pressure gauge, tensiometer, etc. UNCONTROLLED: indicates that water is flowing although no command has been given to open a valve, i.e., burst pipe or leak

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UNOPENED: indicates a valve's failure to open although commanded to do so HIGH FLOW: indicates that a greater than desired discharge has taken place LOW FLOW: indicates that a lower than desired discharge has taken place

The last four of the above statuses are considered alarm conditions. The Matarol® displays an alarm condition which may be relayed via a paging system to the operator. Parameter Table This table includes fixed parameters that do not change from one schedule to the next. Data must be entered under the following headings: • • • • •

•

HIGH FLOW: the percentage deviation by which the actual discharge is allowed to exceed the nominal discharge EMERGENCY INTERVAL: the time during which predetermined valves irrigate when the emergency program is activated (by thermometer, tensiometer, etc.) EMERGENCY VALVE: the numbers of the valves which operate in the emergency program TENSIOMETER START TIME: the time at which the tensiometer condition is read FERTILIZER WATER RATIO: this column determines the type of fertilization required — either quantitative or proportional. With the column empty quantitative fertilization takes place. A discrete quantity of water irrigates the land, followed by a quantity of fertilizer, followed by a final quantity of water. With the digit "1" entered into the column, proportional fertilization takes place. With each pulse from the water meter a preprogramed quantity of fertilizer is injected with the water WATER METER: either "1" or "10" is entered into this column, depending on the type of water meter to which the Matarol® is connected (a pulse every 1 or 104 of fertilizer)

Set-Time Table The time of day and the day of the week is entered in this table. The MIR® 3000 The MIR® 3000 is the most recent control system which was introduced in 1981. It is an intermediate unit between the most comprehensive MIR® 1080 and the small unit Matarol® 2000. It can perform most of the MIR® 1080 on a smaller scale. The main advantage and characteristic of this unit is the newly developed field unit which can provide only two commmands and receive 2 back indications. Thus it is a small unit which is installed at each valve, pump, sensor, etc. and eliminates the need for control hydraulic tubing. The MIR® 3000 is also less costly than the MIR® 1080 and it can control large areas of the range of 100 to 500 ha. This unit can be used also as a terminal in CCT or HCU systems.

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IRRIGATION MANAGEMENT AND SCHEDULING Ilan Amir INTRODUCTION An irrigation system is a comprehensive system which contains two main components: (1) hardware — the hydraulic network and (2) software — the operation plans. Once the hardware is set up, the software entirely dominates the actual performance of the system in order to meet crop-water demands. Management of irrigation is the answer to the question, when to irrigate a certain set of plots with predetermined quantities of water. Although a simple question, the answer becomes more and more complicated, depending on the constraints imposed on the planner. The more constraints there are the more complicated is the process of scheduling. The end products of such a process are irrigation time tables which present the amounts of water required in place and time. The tables should include all the information required by the irrigator, namely, when to open and shut certain valves, pressure head and discharge distributions, and the working points of pumps. One of the main factors implicitly involved is uncertainty. It arises as a result of the fact that the planner does not control several factors such as weather, pump and equipment failures, insect attacks, etc. Therefore, frequent changes are expected to adapt the irrigation scheduling in order to minimize crop hazards. These expected, but unforseen changes necessitate rapid response. Further more, constructing an irrigation time table and the expected changes, in particularly, should meet local and subjective constraints, some of which cannot be quantitatively formulated and, therefore, cannot be explicitly ranked by clear priorities. It is, therefore, very difficut, or even impossible, to optimize such an irrigation time table due to the following: 1.

2.

3.

It is very hard to formulate a proper economic objective function, since the water-yield production functions are not known quantitatively. Even in cases where the average relationships between water amounts and crop yields are considered known, the sensitivity, i.e., the effect of advancing or delaying a single irrigation by a few days on the yield, is almost always not known. Most of the constraints regarding irrigation management are of a strong local and subjective nature and thus cannot be formulated in a comprehensive model which should consider all the situations, and which, on the other hand, has to be kept reasonably simple. From the model efficiency point of view, the hydraulic calculations had better not be incorporated in an optimization model because of their nonlinearity and the large number of various hydraulic events occurring over the entire irrigation season.

Consequently, a practical procedure for obtaining an admissible (rather than optimal) schedule is to give the user a decisive role in constructing a search for a satisfactory time table which is hydraulically feasible and meets his self-imposed individual constraints and subjective priorities, by a step-by-step process. The following is a description of such a process, based on a systematic and hierarchical approach. The process is divided into two main stages: (1) the scheduling of water amounts and (2) the hydraulic computations, to be explained by means of flow charts.

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FIGURE 1. Flow chart of a systematic approach to constructing irrigation time tables.

SCHEDULING OF WATER AMOUNTS Figure 1 presents a flow chart for this stage and should be followed. The first step is to prepare the data required for the irrigation scheduling. The data includes the following: plots to be irrigated, amounts of water to be applied to each plot, dates of

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irrigation (intervals), number of recommended dry days (without irrigation) in the intervals, the irrigation equipment, its nominal discharge and its minimal head (pressure) required for proper functioning, number of hours during which the irrigation, by a given equipment, is required (e.g., sprinkling during wind is not desired, therefore, the number of hours indicated excludes windy hours), and number of hours permitted for pumping. When this step is completed, one can construct the desired time table, either graphically or by means of tables, by summing up the amounts of water required for each plot and for every day of the irrigation season. Check whether or not all the amounts can be supplied by the hydraulic network for each day. If the answer is yes, then go to the hydraulic calculation step (HCS) under two conditions: (1) if there exist yearly and monthly quotas (as in Israel, for example), then the desired distribution has to meet these quotas and (2) the maximal daily amounts required are not larger than the network capacity. If one (or more) of these requirements is violated, then the desirable time table is not feasible and the following systematic procedure is suggested: 1.

2.

If the yearly quota is not met, check whether or nor an additional amount of water is available and economically justified. If not, then the possibilities are either to reduce the desired water amounts for certain crops or to reduce the irrigated area. If the monthly quota is not met, the possibility is to check whether or not a certain amount of water may be transferred to another month without violating the monthly quota.

When (1) and (2) are satisfied, then the problem lies in one or more of the daily amounts required. There are several possibilities to overcome the problem, but first one has to evaluate the unsatisfied excess of water, D. "Wind" policy — The daily water amount is calculated by multiplying the hourly discharge by number of hours without wind (in case of sprinkling). Therefore, we can increase the daily amounts by lengthening the irrigation duration. By doing so, we must take into consideration the fact that crops might suffer. In this case the actual decision is to be taken according to personal preferences and priorities. If this policy solves the problem, i.e., the additional amount is greater than D, then go to HCS. Otherwise, go to "The Displacement Policy". Since the displacement policy evolves many alternatives, the actual construction of an irrigation time table becomes a complicated task. To make this step easier, computerized interactive programs have been developed* as an aid to the irrigation planner. It is, therefore, preferable to explain the displacement policy, using the approach adopted in the computerized aid. THE COMPUTERIZED AID FOR THE DISPLACEMENT POLICY Figure 2 shows the structure of the computerized aid as a four-level tree of options, where an option is a computer program dealing with a limited aspect of the irrigation displacement policy. The programs are written in a prompting mode in APL (A Programming Language) offering (at every stage) the options available, the formats required, and how to activate the computer. *

The computerized aid has been developed by a joint team including the I.B.M. Israel Scientific Center and D. Nir and the author of the Faculty of Agricultural Engineering, Technion — Israel Institute of Technology, Haifa, Israel. At the present stage, this interactive aid has been published as a User's Manual 7 and has been successfully applied on many kibbutz farms in Israel.

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FIGURE 2. policy.

Structure of the computerized aid for the displacement

When SYSTEM is entered as the first level, the computer offers the following second level three options: (1) NETWORK, (2) TIME TABLE, or (3) SOLVER, and asks for the desired option. When (1) is entered (NETWORK) the user has two options: (1) INPUT; or (2) DISPLAY. The INPUT option is for entering new data or updating existing data, while DISPLAY option presents the data which is already in the system. Both INPUT and DISPLAY have four additional, fourth-level options: (1) PIPES, (2) NODES, (3) PUMPS, and (4) SOURCES which are related to the various components of the hydraulic network, respectively. When the user completes the NETWORK options, the entire data concerning NETWORK is stored in the memory of the computer, forming the hydraulic basis of all of the branches of the other second-level options, namely TIME TABLE and SOLVER. The SOLVER is for the hydraulic calculation step (HCS) and will be presented later. TIME TABLE comprises five third-level options: (1) INPUT, (2) DISPLAY, (3) GLOBAL DISPLACEMENT, (4) LOCAL DISPLACEMENT, and (5) MEMORY OPERATIONS. The first, two, INPUT and DISPLAY, are provided for input/output related to the time table. The GLOBAL DISPLACEMENT option is the most important aid for constructing the time table. It modifies the current irrigation time table by shifting the first date of an irrigation using one of the methods of the fourth level.

THE DISPLACEMENT POLICY The displacements of the irrigations are related to both plots and subblocks. A plot is the smallest unit of land of a certain crop, which is to be irrigated concurrently by a

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single main valve or a group of several valves close to each other. A subblock comprises several plots in which only one plot can be irrigated at a time. Examples are (1) several plots, which have only one set of sprinkler pipes which is shifted from one plot to another and (2) several plots which have their own irrigation equipment but cannot be irrigated at the same time due to agromechanical treatments. The computer programs under consideration deal with subblocks as the smallest units to be displaced. It is obvious, however, that when desired, a plot can be viewed as a subblock comprising this single plot. Three options of the GLOBAL DISPLACEMENT — MINIMAX, MINIMUM VARIANCE, and MAXIMAL DAILY DISCHARGE — automatically carry out the displacement of the irrigations through built-in programs. The displacements are limited by two considerations to be introduced into the computer by the following values: (1) two numbers designating the number of days the user is prepared to advance or delay the first date of each of the irrigations for all the subblocks. These two numbers, when added to the existing irrigation durations, create time ranges within which the irrigations are to occur and (2) displacement priorities which determine the order by which the subblocks are to be shifted. (Assigning a very high priority to a certain subblock would, in fact, allow no displacement). In this context, it should be implicitly understood that the original unshifted dates are considered optimal. As mentioned earlier, there are three built-in options based on the following different methods: 1.

2. 3.

MINIMAX reduces the maximal peak of either total irrigation flow on a given day or the total daily water demand for a given day (depending on the data entered). Since the search for the minimax is local and does not find the global optimum, one could (or perhaps should) activate this option several times until no further improvement is achieved. MINIMUM VARIANCE constructs a well-balanced irrigation time table such that the variance of the daily water demands, or of the total irrigation flow, is minimized. MAXIMUM DAILY DISCHARGE constructs a time table which stays within the limit of total available daily discharge while searching for the shortest period of time required for irrigating all of the subblocks. This option obviously ignores the predetermined ranges of the allowed displacements previously explained.

In cases where these three options are not sufficient, i.e., do not provide a feasible time table, the user still has the other four options of the GLOBAL DISPLACEMENT. These additional options provide the system with more possibilities of displacements and thus allowing further improvement of the time table. It should be noted that the global displacement options maintain the original intervals between irrigations for all subblocks and, thus, do not change any subblock irrigation regime over the entire irrigation season. It may happen, however, that the global displacement policy does not solve the problem, i.e., several days have peak demands that could not be satisfied by this set of options; therefore, go to the local displacement policy. LOCAL DISPLACEMENT POLICY Further improvements might be obtained using LOCAL DISPLACEMENT options. These options operate on a single irrigation and therefore do not necessarily maintain the original intervals between irrigations. They enable one to shift only one irrigation, to insert a dry day (or more) while interrupting the continuation of a given irrigation,

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etc. This is done, of course, on the time table obtained by the GLOBAL DISPLACEMENT options. Now, if the peaks still cannot be supplied, one has two additional possibilities, reduction of water amounts for certain crops or relative reduction policy.

REDUCTION OF WATER AMOUNTS FOR CERTAIN CROPS The y% Policy (see Figure 1) The necessity of using this policy rises when all the previous steps are not sufficient. According to this policy, the planner reduces a certain amount of water from one or more plots to be irrigated in the problematic days. This policy is justified under two conditions: (1) the reduced amount does solve the problem and (2) the reduction is economically justified and acceptable by the planner (in most cases, such considerations are not quantifiable). If this policy is still not sufficient, then consider the last possibility, relative reduction policy. RELATIVE REDUCTION POLICY According to this policy, one reduces the amounts of water for all the plots irrigated in the problematic day, relative to amount of water which cannot be supplied, D, as follows: 1.

Calculate 0y,d

2.

Check

3.

n = number of plots to be irrigated during the d-th day. Calculate ($hd x D for each plot j, where D is the difference between the amounts of water required and those supplied.

4.

Subtract for each plot j /?„„ x D from the desired amount of water.

This last policy ensures that all of the new reduced amounts of water can be supplied every day. However, the time table achieved, after such a long and sometimes tedious process, is not completed as long as hydraulic computation step (HCS) has not been applied. Hydraulic Computation Step — HCS For complicated networks, this step requires a hydraulic solving algorithm which evolves nonlinear equations such as Hazen-Williams equations). Referring to the computerized aid, this step can be carried out using the last second level option — SOLVER. This option solves the hydraulic situations that have been determined by the previously described time-table options; i.e., the discharges at every irrigating node (valve) required by the time table obtained are the inputs for the SOLVER, where the outputs are the pressure heads. The mathematical method of the SOLVER has been fully described elsewhere (Brailovsky and Rodeh5).

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The network solver provides the following information: 1. 2. 3. 4.

Pressure heads and discharges at irrigating valves according to the time table The working points (pressure head-discharge) of all of the pumps Pressure head loss, discharge, and direction of flow either for every specified pipe or for all pipes (optional) Pressure head at every specified node or for all nodes (optional)

The information provided by (3) and (4) is essential for determining the bottlenecks in the network and for a better understanding of its performance. SOLVER has some more options which enable one to consider temporary changes; that is, when one wants to check whether or not a suggested slight change in the network is efficient hydraulically and improves its performance in general or for specific days. These changes do not affect the data already entered, unless they improve the network efficiency substantially. So far, the network solver has proved its efficiency in solving quite complicated networks (22 loops, 7 different water sources, and some 300 pipes). It is now in wide use in Israel.

CASE STUDY The case study is an application of the described computerized aid on an irrigated cotton field of 580 dunam (1 dunam = 0.1 ha, is the unit of land area commonly used in agriculture in Israel). The cotton is operated by a highly experienced team of kibbutz Ein-charged. This particular field is only a part of the cotton area of this kibbutz, totaling in 4500 dunams. In the region where the kibbutz is located (center of the northern region of (Israel), cotton receives five irrigations as follows: May 5 — 90 mVdunam June 19 — 120 mVdunam July 1 — 100 mVdunam July 13 — 100 mVdunam July 25 — 50 mVdunam

The total amount of water per dunam is 460 mVdu (4600 mVha). The intervals between the last four irrigations, which occur during the main irrigation season, are 12 days each. Figure 3 shows the layout of the cotton field under consideration. The water source is a reservoir which serves the entire irrigated area of the kibbutz, while the pump serves mainly the 580 dunam cotton field. The pump, located in pipe number 200, is of a horizontal type, having the following characteristics: Discharge (mVhr) Pressure head (m)

300 118

350 118

400 177

450 115

500 110

550 103

600 93

The division of the field into three subblocks has been originally suggested by the farmers according to their past experience. Each of the subblocks has its own set of portable sprinkling equipment. The irrigation equipment sets consist of several sprinkler pipes of 180 m length (which determines the length of the plots). The sprinklers are Na'an 233/94 with a nominal discharge of 1.41 mVhr at 30 m pressure head. The minimal pressure head required at the main valve supplying the set of pipes in order to achieve proper water distribution is 40 m. The sprinkler pipes are shifted by a tractor from one plot of the subblock to the next.

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FIGURE 3. Example of an irrigated cotton field.

As can be seen from Figure 3, subblock 1 comprises eight plots (1 to 8); subblock 2, eight plots (9 to 16); and subblock 3, seven plots (17 to 23). Table 1 presents the irrigation time table based on the 12-day intervals as has been suggested by the farmers. This table indicates, in addition, the area of each plot, the discharge required at the irrigating valves, and the number of valves from which the plots are to be irrigated. The main problem posed by the farmers was the fact that they could not manage to reduce the number of the irrigating days in the interval, i.e., 12 irrigating days within a 12-day interval. Obviously, this situation does not leave any extra day to meet possible pump failures and other disturbances during the irrigation interval. Therefore, the computerized search has been directed mainly to solve this problem, i.e., to reduce the number of the actual irrigating days within the 12-day interval. The work on this case was carried out in several steps, as follows. Step 1 — Data The hydraulic network data was introduced into the computer, including: pipes (number, length, inner diameter, Hazen-Williams coefficients, and two node numbers indicating the beginning and the end of each of the pipes), nodes (number and elevation) pump: numerical presentation of its characteristic curve and the number of the pipe where it is installed, and sources — number of the node where the water source is located (200, see Figure 2). The formats for entering the data are fully explained by the computer programs. Step 2 — Calibration Several parameters involved in the network are approximated empirically, such as Hazen-Williams (H-W) roughness coefficients and local pressure-head losses (due to valves, pressure regulators, bends, pipe restrictions, etc.) In order to obtain reliable hydraulic results, one must calibrate the network solver. That is, for a typical hydraulic event a comparison between observed and calculated discharges vs. pressure heads is to be carried out. Generally, it has been found that the most efficient way for approximating the local pressure-head losses is to change (reduce) the H-W coefficients. Such a calibration has been done in our case resulting in reducing several of the H-W coefficients. It should be emphasized that although the calibration process requires additional effort, this step is essential. Step 3 — Checking the 12-Day Interval In spite of the fact that this interval had been suggested by the farmers according to their experience, it was hydraulically checked and analyzed for the following two purposes: (1) to check whether or not all irrigation events involved in this time table are feasible hydraulically and (2) to determine the bottle necks in the network and to point out the reasons which made it impossible to shorten the interval.

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Volume II Table 1 A 12-DAY INTERVAL TIME TABLE FOR COTTON FIELD Plot no.

Area (dunams)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

13 19 25 27 27 27 24 29 23 27 27 27 27 27 24 26 30 30 30 30 30 22 17

Number of Total Irrigating Irrigation day number in the interval sprinkler discharge valve pipes (mVhr) number 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 5 7 9 10 10 10 10 10 10 10 10 10 10 10 10

10

11

11

11

11 11 9 7

99 148 190 211 211 211 183 225 183 211 211 211 211 211 183 201 197 232 232 232 232 172 132

205 205 209 209 214 214 219 219 206 206 210 210 215 215 220 220 208 208 211 211 217 217 222

X X X X X X X X X X X X X X X X X X X X X X X

The computer outputs indicated the following: 1.

2.

Most of the events are hydraulically feasible, i.e., at every irrigating valve there was a pressure head of at least 40 m. However, for two of the events, the pressure heads were 32.42 and 35.15 m at nodes number 222 and 208, respectively, when irrigating. These reduced pressure heads were recognized by the farmers, confirming that the water distribution through the sprinklers suffered significantly. It was clearly pointed out that the bottlenecks of the network were the pipes 201, 203, 205, 206, 207, and 208. In the main pipe 201, the head loss increased up to 30m in most of the hydraulic situations (see Figure 2).

Step 4 — 11-Day Interval* In order to reduce the number of the irrigating days and thus to leave a spare day for meeting possible irrigation or pump failures without adversely affecting the hydraulic performance of the network, it was suggested to divide the entire field into four subblocks instead of the original three. This division adds a degree of freedom in the process of the global displacement and reduces the discharges at every irrigating valve, since the plot sizes are also reduced. On the other hand, due to the reduction of the number of the sprinkler pipes shifted as a set and the resulting increase in the number of the sets (four instead of three), it increases the labor required for shifting the sets. The new 11-day interval time table has been obtained using both the option MINIMAX of the GLOBAL DISPLACEMENT and the option DRY DAY of LOCAL DISPLACEMENT and checking it hydraulically by the option SOLVER. *

The term "11-day interval" is not very accurate; in fact, it denotes 11 irrigating days in a 12-day interval. But since this term is used by the irrigators and is clearly and correctly interpreted, it is being used in this presentation.

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CRC Handbook of Irrigation Technology Table 2 GRAPHICAL PRESENTATION OF THE 11-DAY INTERVAL

Subblock 1° Subblock 2 Subblock 3 Subblock 4

1

2

3

4

5

6

7 8

9

X

X

X

X X X

X X

X X X X X X

X

X

X X

X X

X X

X

X

X

10

11

X X X

X X X

Surprisingly, it was found that this time table met the main hydraulic constraint, namely minimal pressure head of 40 m at every irrigating valve, making this solution feasible. Table 2 shows graphically the 11-day interval and Table 3 presents the resulting pressure heads at every irrigating valve as has been calculated by the computerized aid. From Table 2 it can be seen that the 11—day interval time table involves up to three dry days, imposing some difficulties in the execution. In spite of these difficulties, the farmers accepted this time table since it left an extra day. Such a preference is entirely up to the user, reflecting his experience and many other personal considerations involved which could not be quantitatively formulated. It is also a typical example which demonstrates the main concept on which the computerized aid is based, namely, to enable the user to direct the search until the time table is satisfactory to him. Table 3 presents the 11-day interval time table and the hydraulic solutions of the various irrigation events. One can see that the pressure heads are not less than 41.68 m and, for most of the valves, they are significantly higher. Also for this case the network performance has been checked and analyzed by using the path of options: SYSTEM-SOLVER-DISPLAY, by which one obtains the pressure head losses, the discharge, and the flow direction for every pipe. This option clearly pointed out that for this time table, the hydraulic bottleneck of the network is the main pipe (No. 201), through which the total discharge flows, where the head pressure losses exceed 28 m. Step 5 — Improving the Network As a result of the above-mentioned hydraulic solutions, it became quite clear that improving the network was quite essential. While checking again the layout of the network, a connection between the nodes 208 and 201 (Pipe No. 204 — dotted line, Figure 3) has been indicated. The additional line creates a loop in the network. This simple change, when introduced (length — 40 m; inner diameter — 145 mm), improved the performance of the network dramatically. Obviously, it increases the pressure heads in the area irrigated by the pipes 205, 206, 207, and 208, and also reduces the head losses in the pipe 201 due to the reduction of the total discharge, now divided between two pipes. Quantitatively, the head loss in pipe 201 is reduced from 28 m to only 6 to 8 m, according to the discharge distribution in the network. (This solution has been carried out using the paths: SYSTEM — NETWORK — INPUT — PIPES and SYSTEM — SOLVER — SOLVE). Step 6 — 10-Day Interval The improvement of the network, described in Step 5, indicated consideration of further reduction in the number of irrigating days. Furthermore, since the 11-day interval of four subblocks imposed some execution difficulties and increased labor, it became evident that one should try to construct a new time table for the original three subblock division. Again the MINIMAX option has been used and further local displacements have been carried out by the INSERT DRY DAY option (see Figure 1).

Table 3 THE 11-DAY INTERVAL Irrigating valves

Day in the interval 1 2 3 4 5 6 7 8 9 10 11

Number

Discharge (mVhr)

Pressure head (m)

207 207 211 208 208 212 212 206 206 205 205

160 170 170 160 170 170 170 160 170 110 140

65.02 61.90 71.46 67.23 80.76 75.48 77.15 67.84 72.46 70.70 67.52

Number

Discharge (mVhr)

Pressure head (m)

209 209 214 211 214 217 217 217 217 210 210

150 150 150 170 150 170 130 170 170 170 170

60.27 59.23 41.68 66.58 59.43 67.13 74.59 72.07 82.95 71.87 72.15

Number

Discharge (mVhr)

Pressure head (m)

Total discharge (mVhr)

215 215 220 220

170 170 150 170

53.26 52.39 43.01 44.33

219 219 222

130 150 100

40.71 42.16 63.12

222 222

130 90

66.61 73.07

480 490 470 500 320 470 450 430 340 410 400

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Table 4 shows graphically the 10-day interval obtained and Table 5 presents the hydraulic solutions of this interval's irrigation events. In this regard, it should be noted that since the farmers did not believe that the 10-day interval could be feasible, they set aside plot number 23 to be irrigated separately by trickle irrigation. From Table 5 one can easily see that the pressure heads at each irrigating valve exceed significantly the minimal value of 40 m. Only five valves have pressure heads ranging from 50 to 60 m, while in most of them, pressures are higher and even exceed 80m. Consequently, it becomes obvious that further improvements are called for in two directions: (1) to increase the total cotton area to be irrigated by the same equipment and (2) to try and decrease the number of the irrigating days. Since the work on this case was carried out during March and the irrigation season starts in May, the farmers were not able to adopt and to execute the changes indicated by the above-mentioned two directions due to time shortage. This 10-day interval time table, however, will be introduced in the following irrigation season. For carrying out this case study, 1 day was spent for gathering, arranging, and entering the network data and several hours to complete the entire search. The programs were run on the IBM® 5110 computer requiring approximately 3 min C.P.U. time. CONCLUSIONS This chapter presents a systematic approach for the construction of irrigation time tables. It provides a hierarchical structure of policies and describes a computerized aid which helps the planner to evaluate various alternatives. The main conclusion is, definitely, that the planner has the most important role in this process. Any model and aids can only help but cannot replace the human considerations. However, applications using the described aid point out the following: 1. 2. 3. 4.

5.

The need for entering detailed data concerning the hydraulics of the water distribution network improves in itself the user's familiarity with the system. From the solutions obtained, one may improve (sometimes significantly) both the network and the management of the irrigation process. The fact that the user has a significant role in directing the search for an admissible time table enables him to overcome the difficulties in introducing and considering unquantified personal preferences. The interactiveness of the set of programs and its rapid response make it both possible and practical to check and analyze many alternatives which otherwise would have not been considered — especially so in cases of networks that contain loops. In our experience, the rapidity of entering new data and obtaining solutions justifies the consideration of many alternatives, even those which, to begin with, do not seem to be very promising. Although the computerized aid has been developed for operation by the farmer, our experience shows that a collaboration between the farmer and the agricultural engineer is preferred in order to use the set of the programs efficiently.

Table 4 GRAPHICAL PRESENTATION OF THE 10-DAY INTERVAL

Subblock 1 Subblock 2 Subblock 3

1

2

3

4

5

6

7

8

9

10

X

X

X X

X X

X

X

X X X

X X X

X X X

X X

X X

X X

Table 5 THE 10-DAY INTERVAL Irrigating valves Day in the interval 1 2 3 4 5 6 7 8 9 10

Number

Discharge (mVhr)

Pressure head (m)

207 207 206 206 205 205 209 209 214 214

176 215 165 190 60 104 146 170 170 170

104.46 102.80 95.30 94.34 88.36 87.52 73.73 76.81 53.54 51.98

Number

Discharge (mVhr)

Pressure head (m)

219 219 211 211 210 210 215 215 220 220

148 183 210 210 190 190 190 190 165 180

64.77 59.40 83.22 82.49 78.19 79.47 56.40 65.68 53.94 50.70

Number

217 217 222

Discharge (mVhr)

210 150 110

Pressure head (m)

76.44 88.40 66.72

Total discharge 324 398 375 400 460 444 446 360 335 350

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CRC Handbook of Irrigation Technology REFERENCES

1. Amir I. and Shamir, U., A computerized program for constructing irrigation time-tables (transl.), Tec/i/77071 Fac. Agric. Eng., P.N. 21/72, 1977. 2. Amir, I., Friedman, Y., Sharon, S., and Ben-David, A., A combined model for operating irrigated agricultural systems under uncertainties, Trans. A.S.A.E., 19, 299, 1976. 3. Amir, I., Irrigation time-tables, in Irrigation Engineering, 3rd ed. (transl.), Ben-Ami, A. and Ofen, A., Eds., 1980,242. 4. Amir, I., Gofman, E., Pleban, S., Nir, D., and Rodeh, M., Computerized scheduling of complex irrigation systems, Trans. A.S.A.E., in press. 5. Brailovsky, M. and Rodeh, M., An Improved Hydraulic Network Solver, IBM — Israel Scientific Center, TR-065, 1978. 6. Gofman, E. and Rodeh, M., An Interactive Aid for Constructing Irrigation Time-Tables, IBM — Israel Scientific Center, TR-069, 1978. 7. Gofman, E., Pleban, S., Amir, I., and Nir, D., An interactive aid for constructing irrigation timetables and solving hydraulic network — user's manual (transl.), Technion — Israel Institute of Technology, Faculty of Agricultural Engineering and the IBM — Israel Scientific Center, P.N. 292, 1979.

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IRRIGATION OF COTTON Yacov Ayalon INTRODUCTION Cotton is the most important fiber plant in agriculture. In 1980 the areas of the world planted with this crop covered 33 million ha, or 82,500,000 acres. These areas range from 42° N to 35° S latitude, wherever the temperature is adequate (see Figure 1). Most of the cotton is rain fed and only a small portion is irrigated. In the arid zones where the rain is insufficient, less than 250 mm/year, cotton is grown under full irrigation. Under correct irrigation the yields may reach higher levels, because it is possible to provide optimum moisture conditions in the soil. The less the natural precipitation during the growing season, the greater is the possible control of the moisture regime by means of irrigation. This advantage may result in yields which fully offset the cost of irrigation. It may be expected, therefore, that an increasing proportion of the cotton grown in the world will be based upon irrigation. Irrigation must, however, be accompanied by carefully designed measures for water management, drainage, and control of soil salinity. CLIMATE Because of variations in precipitation on one hand and evapotranspiration on the other, world climates can be divided into categories that have a direct influence on the water management for cotton. Humid climates are those for which precipitation equals or exceeds the evaporation demand of the atmosphere for most periods of the year. In principle, irrigation is unnecessary here. Annual precipitation may reach or exceed 2000 mm. Subhumid climates are those where the total rainfall is slightly lower than the humid and the annual distribution is more variable. In many cases there is a short, but marked, dry period. In other cases, there are frequent drought periods. During these dry periods, the evaporation demand of the atmosphere is generally high. Consequently, the water balance of the crops can be upset. If this occurs during critical stages of the crop development, irrigation becomes a necessity. Annual precipitation may vary from 1000 to 1500 mm. Semiarid climates are those where generally two seasons occur: a cold rainy season and a hot dry season. Nonirrigated agriculture is based on winter crops such as wheat, or summer crops such as cotton which, because of the well-developed root system, can use moisture from rains stored in the deep layer of the soils. Under this system, yields are low. Irrigation associated with a hot, dry weather can lead to very high yields of cotton. Annual precipitation may vary from 250 to 1000 mm. Arid climates are those where the annual rainfall is very low, less than 250 mm. These climates are characterized by very high solar radiation, very low humidity, and thus very high evaporation rates. Cotton is grown only by irrigation. SOIL The quantity of water to be applied by irrigation, as well as the frequency and the techniques used in its application, also depend on the nature of the soils and the system of agriculture. As the quality of water, in terms of salt content, is variable, the kind and amount of water applied might modify the properties of the soils and this may

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FIGURE 1.

World distribution of cotton culture.

essentially affect productivity in later years. Some of these problems may be partially overcome by a drainage system to leach out the salt. Selection of soils for irrigation depends on the predicted interaction between water, soil, and the crop. For practical purposes it can be said that the following factors must always be considered in the selection of land for cotton: 1. 2. 3. 4. 5. 6.

Topography and microrelief Depth and quality of groundwater Permeability and water-retention capacity of the soil profile and soil drainage conditions Salinity, alkalinity, and other toxic conditions Texture, mineralogical, chemical, and physical characteristics of the soil profile Depth of soil to hardpan or bedrock

The interrelationships between these factors must be carefully considered. In the world, cotton is grown on a wide range of soil types. Important soil characteristics are the structure and depth, in view of the well-branched pattern of the roots which the cotton plant can develop under good conditions of aeration and moisture. Sandy or shallow soils are not suited to cotton, but in recent years with the development of drip irrigation, it is possible (on these soils) to achieve high yields under suitable moisture regimes. From the point of view of soil fertility a deficiency of certain elements is not serious, as it can be corrected by fertilization. As for salinity, cotton is considered to be fairly tolerant to soil salinity or saline irrigation water, but this has its limits. One should bear in mind that the salts adversely affect the soil structure and indirectly may have a bad effect upon the plant. THE COTTON PLANT Species and Varieties All commercial cotton falls into two groups. The first consists of Gossypium arboreum and G. herbaceum, which have short, coarse fibers and low commercial value. They originate in Africa and Asia, but are today being replaced by the more valuable American species. The second group originates from Central and South America, and includes G. hirsutum, which has a medium length fiber, is strong, and is known as upland cotton. The varieties of this species are the most widespread in the world. G. barbadense is a cotton with a very long fiber which is smooth, fine, and of high commercial value. Because of its high price its use is limited. The Egyptian cotton belongs to this variety.

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FIGURE 2.

107

Cotton root development in early stages.

FIGURE 3. Cotton root development to maturity.

Root System The root system of the cotton plant can reach great depths. The tap root grows quickly immediately after germination. It elongates at an average rate of 2 to 2.5 cm (1 in.)/day in the first months. The normal development of the root system is dependent largely upon the soil moisture and the physical condition of the soil. In the upland varieties the roots reach and extract water from a depth of 2 m (6 ft). This characteristic is taken into account in planning irrigation and water management in arid zones and on deep soils, so that an adequate water supply can be provided at all times to the full depth. The root development right after germination is shown in Figure 2. The later stages of root development are shown in Figure 3.

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The soil moisture regime has a strong influence upon the root development and its profundity. If the cotton is planted in dry soil and the irrigations are relatively light and frequent, the root system is developed mainly in the upper layers of soil. This plant will be sensitive to drought and it will be necessary to continue with light frequent irrigations throughout the growing season. When the irrigations are less frequent and fewer, relatively more water will be used from the deeper layers, but even after a deep root system has been established, the secondary roots will be concentrated mainly in the upper 90 cm. About 60% of the water is extracted from the top 60 cm (2 ft) of soil, and about 75% from the top 90 cm (3 ft). Small amounts are used from 120 to 180 cm (the fifth and the sixth feet) of soil. The depth of wetting, irrigation frequency, and date of the last irrigation affect root distribution and the pattern of moisture extraction from the various soil profiles. Root growth may also be limited by such factors as high water table, plow soil, dry soil, hard pan, heavy clays, salinity, gravel, and other factors. Too much cultivation, or working the soil when it is wet, will compact the soil so that both water penetration and root development will be limited. In one study in California by Stockton, 7 the change in the root distribution with the growth of the plant was found to be as shown in Table 1. Stages of Growth of Cotton 1. 2. 3. 4. 5. 6.

Emergence: 6 to 10 days after germination Appearance of first true leaf: 10 days after emergence Appearance of first square: 35 to 55 days after emergence Appearance of first flower: 21 to 23 days after the square Open boll: 55 to 60 days after early flowering or 65 to 90 days after later flowering (because of shorter days and lower temperatures) Flowering period: 4 to 6 weeks; because of natural shedding of many reproductive parts only 40 to 50% form ripe bolls

The stages of development of upland cotton in California occur approximately during the following periods: Plant establishment Fruit formation Fruit maturation Defoliate Harvest Square formation Boll establishment Fiber development Boll opening

1 April to 15 June 15 May to 20 August 15 July to 15 November 1 5 September to 20 October 1 October to 30 November 15 May to 20 August 15 June to 30 August 15 July to 10 October 15 August to 20 November

WATER REQUIREMENTS OF COTTON Consumptive Use Cotton is grown in many parts of the world, in regions of varying altitude, temperature, precipitation, day length, and length of growing season. Consequently there is great variation in the consumptive use by the plant from one region to another and in a given region from year to year. But in all cotton growing regions, despite the variations, the consumptive use follows a typical curve. It is low at the start of the growth and increases with the development of the root system, increase of leaf surface area, and in arid regions with the rise in temperature and lengthening of the photoperiod. The consumptive use reaches a peak generally at the time of flower and boll formation.

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Table 1 PERCENTAGE DISTRIBUTION OF COTTON ROOTS AT DIFFERENT DATES Soil depth

1 July

21 August

30 60 90 120 150 180

66.0 26.0

20 25 19 18 12 6

6.0 1.2 0.5 0.3

Note: The cotton was planted in April.

Toward the end of the season it declines when the bolls ripen and the temperature begins to drop. This typical curve is shown schematically in Figure 4 for conditions in Arizona and in Figure 5 for conditions in Israel (coastal region). The rate of evapotranspiration and consumptive use may be derived from the climatic factors such as temperature, relative humidity, evaporation from a free water surface, wind, sunshine hours, and day length. Methods for making these determinations are discussed fully in Volume 1, chapter on "Water Requirements of Crops and Irrigation Rates". For the evaporation pan method it was found in Israel by Fuchs and Stanhill 4 that the pan factor is 0.69. In using the Blaney-Criddle method, it was found in Arizona that K was 0.2 at the start of growth, 1.0 at the peak growth stage, and 0.75 at the end of the growing season. For the reference crop method the crop coefficient, kc (ratio of ET of the crop to Et of grass), varies with the growth stages as shown in Table 2. The various coefficients for the different methods cited above are given as a general indication. For each method the correct coefficients must be determined locally on the basis of experimental work, before they may be used as a basis for planning irrigation operations. The total amounts of water provided for the growing season vary in different parts of the world. For example, tests over many years in California have shown that a seasonal water requirement of 600 mm (24 in.) is suitable for the heavy soils and 700 mm (28 in.) for the lighter soils. In Arizona, with a longer and hotter growing season, 1000 mm (40 in.) are required. In Israel the seasonal amount varies from 350 mm (14 in.) on the coastal plain to 1100 mm (43 in.) in the hotter, drier regions. These values are in addition to a preplanting irrigation of 150 to 200 mm (6 to 8 in.). Critical Soil Moisture Level of Cotton In cotton, the extraction of moisture down to the permanent wilting point causes damage to the plant and reduction in yields. In many cotton irrigation tests it was found that it was permissible to allow the cotton to use the available soil moisture up to a certain point without causing reductions in the yield. This point is called the critical soil moisture level (CSML). It will vary with (1) soil characteristics; (2) climatic condition; (3) cotton variety; (4) stages of growth; and (5) irrigation system. In general the CSML is determined empirically by irrigation trials. In Israel it was found that the CSML for cotton of the Acala variety at full stage of development is reached when 26% of the available moisture remains in the root zone. For the Pima variety on deep soils of intermediate texture with a relatively high water holding capac-

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FIGURE 4. Mean consumptive use for cotton at Mesa and Tempe, Ariz. 1954 to 1962.

FIGURE 5. Consumptive use for cotton in Israel.

ity, it is 18%. However, in commercial fields these points are not allowed to be reached, and the field is irrigated when about 2A of the available water has been utilized. INFLUENCE OF WATER REGIME ON THE COTTON The correct time to irrigate cotton is determined from three sets of data: soil, climate, and plant. The soil factors are the moisture limits (field capacity and wilting point), the volume weight, the existing soil moisture before irrigation, and the depth. Once the CSML has been determined the actual quantities of soil moisture to be extracted by the plant between one irrigation and the next can be easily calculated, as explained in the chapter on "Soil-Water Relationships" (Volume 1). The climatic data is used to calculate or predict the consumptive use by any of the several systems mentioned above. The ultimate and most reliable of all approaches is, however, the response of the plant to different water regimes. Yield In the rainy regions where there is a need for supplemental irrigation, it is difficult to determine the effect of the additional water on the yield, because in these regions

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Table 2 VARIATION IN KC FOR DIFFERENT GROWTH STAGES OF COTTON Stage

Days

kc

From Doorenboos, J. and Kassem, A. H., Yield Response to Water Irrigation and Drainage Paper No. 33, Food and Agriculture Organization, Rome, 1979. With permission.

the rainfall has a dominant influence. The supplementary irrigation between two widely spaced rains increases the yield, but this increase is not easily quantifiable, as it depends upon the preceding rainfall conditions. In regions of fully irrigated cotton there is a direct link between the amounts of water and the yield, up to a certain limit, namely the optimal irrigation. Beyond this limit, additional water results in overdevelopment of the vegetative growth, late maturity, and in some cases rotting of the bolls on the lower parts of the plant. This causes reduction in the yield. On the other hand, applications of water less than the optimum cause limited plant growth and reduced yields. The final yield is a function of the number of ripe bolls and their weight. It is known that the plant produces many buds, and because of genetic factors, it sheds a large number of these, and only some reach maturity. This shedding is natural, but external factors may increase it and reduce the yields. Among these factors water is a major one. Excess water, water deficiency, and irregular irrigation can all increase shedding. There is an important interaction between the water, available nitrogen, and the yield potential of the cotton plant. In general, irrigation tests are accompanied by fertilizer tests in order to find the required rate of fertilizer application under optimal irrigation to get the maximum yields. In deep fertile soils in which the depth of wetting reaches 150 to 200 cm before sowing, it is possible to achieve reasonable yields without further irrigation during the growing season. This is dry-land cotton growing and is practiced in regions where the root depth is fully wetted before sowing time and where during the growing season the temperature and humidity conditions (or evaporation) are moderate. When water is limited in either quantity or time and inadequate for optimal irrigation on all the proposed cotton growing fields, partial irrigation is used on some of the fields. By careful irrigation trials, the yield curve is determined for different water regimes. This curve gives the optimal time and quantity of water for different irrigation regimes such as one, two, three, or more applications during the growing season. The yield curve is important to determine the best allocation of the limited water supply on the farm for maximum returns per unit area and per unit volume of water. A typical yield curve is shown in Figure 6. This allocation must also take into consideration the hydraulic limitations and other factors of production such as labor, equipment, etc. In experiments carried out in Israel it was found that the optimum time for a single irrigation is about 1 week after the appearance of the first blossom, providing that the soil had been wetted to the root depth before sowing, either by seasonal rains or by preirrigation.

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FIGURE 6.

Typical yield curve for cotton.

Vegetative Development The cotton is, by origin, a tropical perennial. In fertile soils, with high temperatures and abundant moisture, the plant tends to luxuriant vegetative growth. This is, in many cases, at the expense of the formation of buds. Consequently, by correct irrigation procedures, quantities, and intervals of application, it is possible to control the vegetative growth and encourage the formation of more buds. The ultimate goal is to achieve the correct proportion between the vegetation and the fruit, for maximum yields. As an indicator for determining the amount of vegetative growth two parameters are used: plant height and leaf area index. Boll Characteristics In many trials it was found that frequent irrigation during the fruiting period produces larger bolls, heavier seeds, and lower percentage of fibers. In stressed cotton, the bolls are relatively smaller, the seeds are lighter, and the fibers percentage is higher. Fiber Characteristics The fiber characteristics of length, strength, and fineness are generally genetic traits of the variety. Nevertheless, environmental factors, especially soil moisture and air temperature, can have a strong direct or indirect influence on these characteristics. Inadequate water supply during the period of boll development has a negative influence on fiber length. Excess water, especially late in the season, lengthens the period of maturation and the bolls enter a relatively cooler period. This prevents the fibers from fully ripening and they have low strength and are less fine. Pest Control The benefits of irrigating cotton are accompanied by several plant protection problems. Pests multiply under conditions of high moisture. Certain diseases are also encouraged by irrigation. Weed control problems are increased with irrigation and therefore the use of herbicides grows with the extent of irrigation. This increases the cost of production. It also requires careful coordination of irrigation and spraying or dusting schedules, without which yields will be adversely affected. Inadequate pest and disease control can have a greater deleterious effect upon yields than inadequate irrigation. Control measures using airplanes can achieve better coordination between fast control and optimal irrigation.

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IRRIGATION PROCEDURES Preirrigation In many arid and semiarid regions the rainfall is not sufficient to wet the soil to the full root depth and it is customary to give a presowing irrigation down to a depth of 150 to 180 cm. This has the following advantages: 1. 2.

3.

It provides a supply of moisture for germination and emergence and for the early stages of growth. The water stored in the depth of the soil will be used by the plant later in the season when there is a deficiency in the upper layers. In the event of irregular irrigation during the year, the cotton tap root can make use of the deeper water. This promotes more uniform, deep root development. At the end of the season after the last irrigation, the plant will continue to use the deep water for the maturing of the last bolls without the need for additional irrigations, which could delay maturation and cause undesirable vegetative growth.

This preirrigation is easy to do before the seeding, when there is less pressure of other irrigation work and the water may be more available. In saline soils the preirrigation flushes the salts down below the root zone. In this case the leaching water quantities are increased. Germination Irrigation This is necessary in the following circumstances: 1. 2. 3. 4.

When for various reasons, the preirrigation was not possible, and the seeding was done in dry soil When the upper soil layers dry out more quickly than anticipated In order to avoid the need for deep sowing To enable preemergence herbicides to penetrate the soil before germination

This irrigation need not be large if there was a preseeding irrigation. If the preseeding irrigation was inadequate the germination irrigation may be larger, but not too much lest there arise problems of soil compaction, leaching of herbicides, etc. First Irrigation After Emergence Generally this irrigation is delayed for a relatively long period. In the first days of the plant growth the water requirements are moderate. The quick penetration of the roots permits the plant to use water stored in the soil and provides adequate water supply to the young plants, even though the soil surface appears to be dry. The time between the seeding and the next irrigation varies with the region, the planting date, climatic conditions, soil type, and the condition of the plants, and may vary from 35 to 75 days. Tests performed in Israel show that the optimum time for this irrigation is at the beginning of flowering, when the soil moisture at 90 cm is not much lower than 50% of the available moisture. In hot regions, where temperatures are high at the beginning of the growing season and the water consumption is high, delay of this first irrigation may restrict growth and reduce yields. In such regions the first irrigation is given earlier, with the appearance of the first buds. Good indicators for the time of giving this irrigation are leaf color, rate of growth, and growth of the crown of the plant. The stem growth depends upon the rate of water absorption and stops when evapotranspiration is greater than water absorption. Stem growth slows down before

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each irrigation and is accelerated after. This rate can serve as an indicator of the moisture content of the soil. The minimum rates which represent water stress and the need to irrigate must be determined empirically in each region. In Israel, for example, on soils of moderate fertility, irrigation is required when the rate of stem elongation is less than 1.0 to 1.5 cm/day, or when the top is shortened by 8 to 10 cm (3 to 4 in.). Tests recently done in Israel show that by measuring the water leaf potential, the suitable time of giving the first irrigation after emergence can be precisely determined. The varying irrigation regime may produce a wide range of water potential in the plant. If this is too high it will cause exaggerated vegetative growth. If it is too low general growth may be retarded. The correct levels of water potential in the plant may be regulated by the frequencies and amounts of irrigation at each stage of growth. More water applied increases the potential and vice versa. By monitoring the potential, the optimum yields can be achieved. In the case of cotton the leaf potential is measured. This is accomplished with a standard pressure cell according to certain established procedures. The test is always performed at the same hour of the day, on representative plants in different parts of the field. The leaf on which the test is done should be the youngest fully developed leaf on the plant. On tests performed in Israel, it was found that optimum yields were obtained when the leaf potential was maintained in the range of 12 to 15 bars. Succeeding Irrigations The period starting with the flowering or the formation of the buds in the hotter regions is the critical period in the formation and development of the cotton fruit. It is also the period of highest water requirements. The roots are close to their maximum depth and the leaf surface is also maximum. Less water can cause shedding of the new fruit. Too much water can cause too much vegetative development at the expense of fruit formation. Consequently, the irrigation should be given according to carefully determined rates which allow normal development and maximum yields. The irrigation is generally given when the available moisture approaches the critical level. This is something close to 1/3 of the available moisture remaining in the root zone of about 90 cm. This limit which varies with the soil type, depth, and the soil salinity must be empirically determined for each region. Actually the entire field does not reach this limit at the same time. Therefore, irrigation should commence when 50% of the available moisture is depleted. This enables the entire field to be irrigated before the last portion reaches the critical limit. By checking the soil moisture at regular intervals and various depths, it is possible to gather information on the water consumption which provides a good basis for determining the irrigation intervals and amounts. In Figure 7 the changes in soil moisture are plotted for a typical cotton field in the Coastal Plain of Israel. A preseeding irrigation filled the soil to available moisture capacity to a depth of 180 cm. Three irrigations were given during the season. At no time was the soil moisture in the upper 90 cm depleted below the critical soil moisture level (CSML), which was 33% of the available. In the depth from 90 to 180 cm the moisture was maintained during the entire season at a higher level. Only at the end of the season was this deeper moisture extracted. Cotton plants themselves can forecast their need for irrigation. After flowering begins, the plant should grow steadily but not luxuriantly. The squares at the top of the plant should be prominent. A few flowers should be visible among the top leaves. When flowers are hidden by the leaves, growth is too rapid and water should probably be reduced. A flower garden effect indicates that growth is restricted and irrigation has been delayed too long. The color of plant leaves and terminal growth may indicate the need for irrigation. A change in the appearance of the plant foliage occurs before signs of wilting appear. Every available guide and indication should be used for deter-

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FIGURE 7.

115

Changes in soil moisture during the irrigation season.

mining when to irrigate cotton. The stage of plant development, the moisture requirements during that stage, the appearance of the plant, and the soil moisture conditions are useful guides in determining when and how much to irrigate. None of the guides used independently is as dependable as two or more used together. Late Season Irrigations During the latter part of the season, the boll maturation period, some moisture stress can be tolerated without adverse effects and may have beneficial effects by retarding vegetative growth and improving the fiber quality without measurable decrease in seed or lint yields. However, care should be taken to avoid serious or prolonged periods of stress until all bolls expected to mature are set. The last irrigation must supply the plant with sufficient moisture to enable the young bolls to reach full maturity. The timing of this application must be based upon the following factors: 1. 2. 3.

Time required for maturation of the small bolls Time required for the opening of all the bolls Proposed date of harvesting

Therefore, the date of termination of irrigation depends upon the state of moisture in the soil, the condition of the plant, the age of the bolls, and the climatic conditions prevalent at the end of the season.

IRRIGATION METHODS Irrigation methods for cotton fall into four groups: surface, subsurface, overhead, and drip. Surface Irrigation This includes flooding and furrows. Flooding In many cotton growing regions this method is used, but it requires large discharges of water and level fields. Otherwise the water distribution is not uniform. The area is generally divided into borders to assure a more equal distribution of the water and this gives good results. When this system is properly used there are no great differences in yield and quality of the cotton as compared to other systems. The details of design of border irrigation are presented in the chapter on "Gravity Irrigation" (Volume 1). Furrow Irrigation This is the most prevalent system of irrigating cotton. The length of the furrow, its depth, and lateral spacing are dependent upon the growing system and soil type. In

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this method as with the previous system, the land must be leveled, but in the case of furrows, the slope is a limiting factor. Generally it is not advisable to irrigate with this method when the slope is greater than 3%. Land leveling required for both methods can create problems of soil fertility when the soil is not uniform in the profile. In many cases, the land leveling concentrates the fertile soil in the low spots, whereas the high points are left with exposed subsoil layers which are less fertile. This can be corrected over the time by the use of fertilizers and green manure. Details for the design of a furrow irrigation system are presented in the chapter on "Gravity Irrigation" (Volume 1). Subsurface Irrigation In this method, water is supplied to the plants below the ground surface. Underground pipes may be used, but more commonly the method is to raise the water table. This method is suitable to light soils with a high percolation rate. The drainage system is very important. Irrigation by raising the water table, where this is possible, is the cheapest of all irrigation methods. Sprinkler Irrigation This method tries to simulate rainfall. It achieves a more uniform distribution of the water and greater control of the rates of water application than any other method. Land leveling with all of its disadvantages is not necessary. The main disadvantage of sprinkling is the high cost of equipment and the technical knowledge required. Many types of sprinklers and other equipment have been developed in recent years. Because of the great importance for cotton of giving correct amounts of irrigation water at the right times, a higher investment in the necessary equipment is justified. High labor and equipment costs have led to the accelerated development of systems for moving pipes and automation. In many fields of cotton, especially in the arid and semiarid regions, the newer methods of automatic moving irrigation are used. Sprinkler irrigation design is presented in detail in Volume 1, chapter on "Sprinkler Irrigation" and details of the lateral move system are presented in this volume, chapter on "Irrigation of Sugar Crops". Drip Irrigation This method is relatively new for cotton. The water is supplied through plastic pipes, generally stationary, which feed the drippers. The plastic pipes are laid on the ground or just below the surface. The method supplies small discharge at low pressures. The water enters the soil and spreads out in a bulb around the dripper and eventually a wetted strip may be created along both sides of the pipe. Between these wetted strips the ground is dry. The main roots of the cotton develop around the wetted volume. The fertilizer is added through the water. Irrigation efficiencies are high; but the investment per unit of irrigated area is also high. Figure 8 shows a typical cross section of the wetted soil under drip irrigation. Details for the design of drip irrigation are presented in Volume 1. In checking the plant response to drip irrigation vs. sprinkling in Israel, more or less equal yields were obtained where the tests were conducted on soil types considered optimal for sprinkling. On the other hand, there is a distinct advantage to drip irrigation on the marginal soils. On these soils normal or slightly more than normal yields were obtained with drip irrigation, whereas the yields under sprinkling were low because of soil limitations such as shallowness, stoniness, coarse texture, low available moisture, and rough topography, as well as unsuitable sprinkling due to low pressure and/or wind distortion. The main use of drip irrigation of cotton is on areas considered marginal for irrigation with sprinklers. The chances of success depend upon careful

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FIGURE 8.

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Soil wetting under drip irrigation.

attention to irrigation technique, fertilization, and correct operation and maintenance of the systems. Under drip the irrigations are given frequently, in small amounts. The root zone is limited to only the wetted portion of the soil volume while the rest remains dry. Nutrients and water are absorbed from a small volume. For this reason great care must be taken with correct fertilizer application through the irrigation system, frequent irrigation intervals, and extending as much as possible the irrigation season. It is customary to irrigate every 3 or 4 days and, in some cases, every 7 days, throughout the entire season. In tests, no advantage was found in shortening this interval. On the other hand, some findings indicate that the intervals could be lengthened to those used in sprinkling. These findings are especially important to the possibility of applying the drip irrigation with portable equipment. At present, drip irrigation intervals of 3 to 7 days are recommended. In soils low in water holding capacity and in cases of shallow wetting, the shorter intervals should be used. In extreme conditions of shallow or stoney soil daily irrigation may be required.

REFERENCES 1. Arnon, I., Crop Production in Dry Regions, Leonard Hill, London, 1972. 2. Ayalon, Y.publications of Israel Ministry of Agriculture (transl.), 1981. 3. Doorenbos, J. and Kassam, A. H., Yield Response to Water, Irrigation and Drainage Paper No. 33, Food and Agriculture Organization, Rome, 1979. 4. Fuchs, M., The use of class A evaporation pan data to estimate water regiment of the cotton crop, /sr. /. Agric. Res., 13, 63, 1963. 5. Levin, I, and Shmueli, E., The response of cotton to various irrigation regimes in the Hula Valley, /sr. /. Agric. Res., 14, 211, 1964. 6. Longenecker, D. E., Cotton production in far west Texas with emphasis on irrigation and fertilization, Texas A. M. Agric. Exp. Stn. Publ. 7. Stockton, J. R., Root Development and Irrigation Practices, West. Cotton Prod. Conf., Fresno, Calif., 1964.

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IRRIGATION OF SUGAR CROPS Herman J. Finkel SUGAR CANE Introduction The sugar cane plant, Sacchararn officinarum L., is the most important source of sugar in the world. It is a plant of great antiquity, originating, according to some authorities, in New Guinea, and according to others, in India. It spread to the Pacific Islands as early as the sixth millenium B.C. and later to the Middle East and the Mediterranean. It was introduced to the New World (first in Brazil and then in the Caribbean islands) mainly by the Portugese Jewish settlers who fled there to escape the Spanish Inquisition and has since flourished in the Philippines, Hawaii, and Australia, thus completing its migration around the world. Examination of a map of the world distribution of sugar cane reveals that it is mainly a tropical crop, growing in regions of substantial rainfall. Even in such regions, however, the irregularity of the rains and the length of the dry season are recognized as limiting factors in the growth of the cane, and interest has developed in supplementary irrigation. Along with this, the area of cultivation of sugar cane is being extended to semiarid and arid regions where full irrigation is a necessity. Along the desert coast of Peru and in northeastern Australia (Queensland) there are extensive plantations of sugar cane based almost entirely upon irrigation. As a result of this development, there has in recent years been an increase in the research on the irrigation of cane. Much of this research has, in the past, been conducted by people trained in horticulture and agricultural chemistry, with insufficient attention being paid to soil physics and to the engineering aspects of the problem. Root System of Sugar Cane The sugar cane is propagated by the planting of a stem cutting from a mature plant, called a sett or a seed. This is nourished by sett roots which quickly emerge from the original cutting. After a period of time, secondary shoots emerge from the ground alongside the original cutting and these send down shoot roots which eventually develop into the mature root system. The shoot roots, emerging from the lower ring of the shoot, are thin and markedly branched, but they eventually become thicker than the sett roots and the latter cease to function and die off. Sometimes three types of roots are described: the buttress roots, which originate from the basal nodes of the shoots and which support the plant; the superficial roots which are fibrous, thinner, more branched, and distributed through the upper 60 cm (2 ft) of soil, and which spread to a radius of 2 m around the plant; and the deep roots which are a ropelike mass of roots growing downward to great depths, limited only by the soil and moisture conditions. Under favorable conditions these may penetrate to as much as 6 m. Many studies have been made of the distribution of cane roots and the results vary with the local conditions. In Mauritius, for example, it was found that the vast majority of the fibrous roots which are most active in absorption occur in the upper 30 cm of the soil. They are most numerous between the radii of 1.00 and 1.20 m from the center of the plant. In Java, shoot roots were found distributed to depths of from 1 to 2 m. The factors which affect the root development are many, including the following: cane variety, soil depth, soil texture, fertility, moisture regime, temperature, wind, and cultivation practices. The factor of moisture regime is of special interest in the present chapter. It has been observed that the cane roots have a relatively high tolerance to both wet

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FIGURE 1. Photosynthesis and growth of sugar cane as a function of moisture stress. (From Ashton, F. M., Plant Physiol., 31(4), 266, 1956. With permission.)

and dry soil conditions and are, therefore, resistant to both drought and flooding. However, this is true when the root system is already well established and deep. New roots will generally not penetrate the water table because of lack of sufficient oxygen, and if, after the root system is well developed, the water table should rise and remain high for an extended period of time, the submerged roots will die and decay. The roots of sugar cane, like those of most plants, will seek to obtain moisture in the easiest possible way. If soil moisture is always kept at high levels, most of the roots will develop in the upper 30 or 40cm. If this is not sufficient, the roots will draw upon deeper layers. However, root hairs will not develop in dry soil. Consequently, in order to insure the deeper distribution of the root system, it is necessary to provide initial moisture down to the desired depth. Thereafter, if soil moisture from rainfall or irrigation is deficient, the root system can draw upon the entire soil profile, and the plant will be more drought resistant. This is achieved in several ways, such as the following. A deep underdrainage system should be provided in regions of high seasonal rainfall, to keep the water table down and encourage deep root development. If there is a prolonged dry season, it is important to enter this season with sufficient available soil moisture in the full depth of the profile. If previous rainfall has been inadequate, an initial, or preplanting irrigation should be given to provide a suitable environment for root development. Water Requirements of Sugar Cane In the growing plant, it is important to maintain the internal water balance and the turgidity. Many physiological processes related to growth, such as photosynthesis, cell elongation, etc. are directly related to the turgidity, which in turn is a function of the water supplied through the roots and the losses due to transpiration. Studies have been made in different parts of the world showing a positive correlation between annual rainfall and growth of sugar cane. These have been done in, among other places, Formosa, Java, and Hawaii, all regions of relatively high precipitation. Where the rainfall exceeds 1500 mm (60 in.)/year and is well distributed, moisture is generally not a limiting factor, and this correlation is less marked. Below this annual value, however, and in regions of even higher total rainfall which is poorly distributed throughout the year, irrigation becomes important. Studies conducted by Ashton1 show that dewlap growth stops before there is either wilt, reduction in spindle growth, or a reduction in the rate of photosynthesis (see Figure 1). When the spindle growth stops there is a reduction of about 25% in the rate of photosynthesis. Further moisture stress further reduces the rate of photosynthesis. As can be seen in the figure, the first sharp break in the rate of photosynthesis occurs at an osmotic pressure (soil moisture tension) of about 1.0 atm, and photosynthesis

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ceases when the soil moisture drops to the permanent wilting percentage. It is seen that between osmotic pressures of 0 and 1.0 the rate of spindle growth is about 3.5 cm/ day. Between 1.5 and 2.0 atm the rate is approximately 1.7 cm/day. At higher soil moisture tensions the rate of growth drops to zero. The so-called "critical soil moisture content" is thus at about 2.0 atm. The actual percentage of moisture in the soil at this point varies, of course, with the water-holding properties of each specific soil and can be determined from the moisture tension curve. For a description of the soil-moisture tension curve and methods for developing it see the chapter on "Soil Water Relationships" in Volume 1. If, for example, the soil in question is the clay loam shown in Figure 9 of that chapter, the 2.0-atm tension is found on the ordinate scale (equal to a metric potential of -200 J/kg), at a water content of 14% by weight. The permanent wilting point occurs at approximately 8.5% for that soil and the field capacity, or Viatm moisture content, is about 22%. The total available moisture content is 22.0 8.5 = 13.5%. The soil moisture available from field capacity to the critical moisture content, when irrigation should be applied, is 22.0 — 14 = 8%. This represents about 60% of the total available moisture. Similar calculations can be carried out for any other soil on which sugar cane is grown, provided that the characteristic moisture tension curve is first developed. Cornelison and Humbert 8 in Hawaii found that elongation of cane is uniform between field capacity and a soil moisture tension of 4 atm. Beyond this point the elongation rates of cane spindle were reduced to half of the normal. In the case of the particular soil on which these studies were made, the critical moisture content at 4 atm represented about ZA of the available moisture. It is advisable, of course, to perform similar studies before designing an irrigation system for a specific region, but lacking other experimental data, it is reasonable to estimate that the critical soil moisture content for sugar cane lies somewhere between 2 and 4 atm on the characteristic curve. If the average soil moisture content of a field is continuously (or frequently) monitored, irrigation can be scheduled accordingly. The time interval between irrigations is usually not a constant, but varies with the rate of transpiration of the plants. This is a function of climatic factors as well as stage of growth. It has been found convenient to establish a correlation between transpiration rate and some easily measured climatic factor such as evaporation of water from a standard pan. An extensive series of trials were carried out by Cowan and Innes6 in Jamaica by various methods. It was found that the ratio between rate of evapotranspiration of the cane after a full canopy was developed and the evaporation from a free water surface, E,/E0, was of the order of 0.58. This provides a method of scheduling irrigation and adjusting the irrigation intervals to the actual consumptive use by the plant, as it varies with climatic conditions such as temperature, wind, relative humidity, sunshine, etc. the combined effects of all of which are integrated in the data on pan evaporation. The method of evaluating the water requirement of crops recommended by the FAO10 12 is explained in detail in the chapter on " Water Requirements of Crops and Irrigation Rates" of Volume 1. It is based upon the use of a reference crop of densely growing grass whose rate of water consumption is called ET0. Coefficients are then presented for various crops (Kc = crop coefficient) which, when multiplied by ET0, give the consumptive use for the given crop. The relationship between ET0 and E0 (the pan evaporation) is given by the relationship ET0 - K^ • E0, where K p is the so-called "pan coefficient". Values for Kp under different climatic conditions are given in Table 8 of the above mentioned chapter in Volume 1. By way of illustration, the conditions under which the Jamaica studies were made would give a K p = 0.75. The ET0 would therefore be 0.75 of the pan evaporation and this provides a basis for comparing the Jamaica results with the recommendations made by FAO.

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CRC Handbook of Irrigation Technology Table 1 KC VALUES FOR SUGAR CANE Crop age (month)

12

RHmin = 70%

24

Growth stages

0—1

0—2.5

1—2

2.5—3.5

2—2.5

3.5—4.5

Planting to 0.25 full canopy 0.25—0.5 Full canopy 0.5—0.75 Full canopy 0.75 To full canopy Peak use Early senescence Ripening

2.5—4 4—10 10—11 11 — 12

4.5—6 6—17 17—22 22—24

RHmin = 20%

Light to moderate Wind

Strong wind

Light to moderate wind

Strong wind

0.55

0.6

0.4

0.45

0.8

0.85

0.75

0.8

0.9

0.95

0.95

1.0

1.0 1.05 0.8 0.6

1.1 1.15 0.85 0.65

1.1 1.25 0.95 0.7

1.2 1.3 1.05 0.75

From FAO Irrigation and Drainage Paper 24, Rome, 1975. With permission.

The water requirements of sugar cane vary considerably with the overall length of the growing season and with the stage of development of the crop. The total growth period varies in different climatic regions of the world, and it also depends upon whether the crop is virgin or ratoon. Virgin plantings grow for 13 or 14 months in Iran, 16 months in Mauritius, 13 to 19 months in Jamaica, 15 months in Queensland (Australia), and from 20 to 24 months in some cases in Hawaii. The ratoon crops have a season of 9 months in Iran, 12 months in Mauritius and Jamaica, and up to 14 months in other places. The growth of the plant may be divided into seven stages which have different lengths of time for a 12- or 24-month total growing season. Values for* Kc of sugar cane under different conditions of relative humidity and wind strength, for each of the growth stages, is given in Table 1 . Doorenbos et al.8a summarize the irrigation of the various stages of growth in the following words: Frequency and depth of irrigation should vary with growth periods of the cane. During the establishment period, including emergence and establishment of young seedlings, light, frequent irrigation applications are preferred. During the early vegetative period the tillering is in direct proportion to the frequency of irrigation. An early flush of tillers is ideal because this furnishes shoots of approximately the same age. During stem elongation and early yield formation, irrigation interval can be extended but depth of water should be increased. There is a close relationship between stalk elongation during these periods and water use, and adequate water supply is important during this period of active growth when the longest internodes are formed. With adequate supply this period is reached early and also total cane height is greater. The response of sugarcane to irrigation is greater during the vegetative and early yield formation periods than during the later part of the yield formation period, when active leaf area is declining and the crop is less able to respond to sunshine. During the ripening period, irrigation intervals are extended or irrigation is stopped when it is necessary to bring the crop to maturity by reducing the rate of vegetative growth, dehydrating the cane and forcing the conversion of total sugars to recoverable sucrose. With the check of vegetative growth, the ratio between dry matter stored as sucrose and that used for new growth also increases. During the yield formation period frequent irrigation has an accelerating effect on flowering, which leads to a reduction of sugar production.

Yield and Quality Cane tonnage is strongly influenced by the available moisture. Good yields in the tropical humid areas, without irrigation, may range from 70 to 100 ton/ha. In the dry tropics and the subtropical zones, with irrigation, the yields will range from 110 to 150 ton/ha. The yield of sugar, however, depends also upon the concentration or sugar

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content in the cane. It is known that forced ripening can be induced by decreasing the moisture content of the stalks. This encourages the formation of sucrose. On the other hand, the forced ripening slows down the photosynthesis and the formation of sugar in the tops. It is a subject for careful research to determine the regime of gradual dehydration to obtain optimum tonnage with high concentration of juice of good quality. Clements et al.7 developed a program of drying over a period of 7 months before harvest. It is based upon a gradual reduction in the leaf sheath moisture content from 82 to 74% over this period. This is achieved by gradually lengthening the irrigation intervals. As a practical procedure, the leaf sheath moisture content should be checked regularly and plotted on a time scale through which the descending line from 82 to 74% is drawn over the 7-month period. Whenever the actual moisture content drops below this optimum line, irrigation should be given. This procedure is more easily accomplished when there is no rainfall. If rainfall is expected during the drying-off period, the cane is permitted to dry more rapidly to reduce the influence of rain which might fall in the final few months. In general it has been found that as the soil moisture tension increases, the reduction in tissue moisture occurs mainly in the newly formed joints. The spindle elongation gradually is reduced until it stops when the permanent wilting percentage has been reached. This ripening process results in the translocation of the sugars from the tops to the stalks. Consequently some research workers have monitored the forced ripening of the cane by checking the moisture in the 8-10 stalk section, which has been proven to be a sensitive and reliable index of maturity. In Figure 2 are shown the results of the sugar content determinations at many different moisture contents. A good negative correlation is obtained between the moisture content and the sugar concentration. Irrigation Methods There are basically three methods of irrigation currently used for sugar cane. These are furrows, sprinklers and drip, or trickle irrigation. The characteristics of each method and the design procedures are covered in detail in the appropriate chapters of Volume 1. In this chapter, the discussion will be limited to the criteria for selecting the method most suitable for irrigating cane under different conditions. Furrow Irrigation This is the oldest and heretofore the most widely practiced method of irrigating sugar cane. It is well suited to a row crop with tall, dense vegetation, growing in large fields of generally level topography. The furrows must be formed before planting, as they cannot later be prepared or repaired when the cane is tall. The water is supplied by canals crossing the furrow heads and the excess water is drained out at the lower ends of the furrows through drainage ditches. As in all furrow irrigation systems, it is important to select the correct length of furrow for the prevailing longitudinal slope, the infiltration rate of the soil, and the rate (or head) of water available. However, in many large cane plantations these criteria have been set aside in favor of a standard length. In Latin American countries this length is called a "tarea", which is the daily task of cultivation and cutting assigned to one worker. The use of this arbitrary criterion may be completely incorrect for the physical conditions of the field in question, but it is said to avoid labor unrest, such as would occur if the rows were made longer. The advantages of furrow irrigation of sugar cane include the following: 1. 2. 3.

Relatively simple Low initial investment Low operating cost if labor is cheap

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FIGURE 2. Sugar content as a function of the moisture content in the 8-10 stalk section. (From Humbert, R. P., The Growing of Sugar Cane, revised ecL, Elsevier, Amsterdam, 1968. With permission.)

The disadvantages include the following: 1. 2.

Low water use efficiency Not suitable on light soils with high infiltration rates, as the furrows, and hence the supply canal spacings will be short 3. Requires large discharges of water 4. A drainage system is almost always required 5. Land is wasted by supply and drainage canals 6. Not suited to rolling topography 7. Irrigation may interfere with other field operations 8. Less suitable to smaller applications of water, such as may be necessary at certain times of the growing season 9. Land leveling often required before furrowing 10. Nighttime operations not convenient Sprinkler Gun Irrigation Because of the disadvantages of furrow irrigation much of the sugar cane is now irrigated by sprinklers. One problem with sprinklers, however, is the great height to which the cane grows. The dense foliage would interfere with the uniform distribution of the water unless the sprinkler head is located above the tops. This requires mounting the sprinklers on very tall risers which must be strongly braced. Because of the tall and dense growth of the mature crop, it is difficult to move the portable supply pipes from one position to another. This negates one of the main advantages of the portable sprinkler system, that of using a minimum amount of equipment over a large area. It has been found, therefore, that the most suitable types of sprinklers for cane fields are the large guns, the central pivot system, and linear irrigation.

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The large sprinkler guns are described in the chapter on sprinkler irrigation in Volume 1. A typical gun, for example, which might be used on cane plantations in the Naan Type 2812 (see Figure 13 in "Sprinkler Irrigation", Volume 1). This gun works on pressures between 5 to 10 atm (75 to 150 p.s.i.) with discharges ranging from 52 to 135 mYhr. The spacings are usually on a triangular pattern from 78 to 96 m apart (256 to 315 ft.). It is thus possible to cover from 0.6 to 0.9 ha (11/2 to 2!/2 acres) per sprinkler with an application of from 10.0 to 14.4 mm/hr (0.4 to 0.6 in./hr). The supply pipes for sprinkler guns of this size may be 6 or 8 in. or more in diameter (depending upon the number of guns on each line), and they are often left in the field throughout the irrigation season. The guns themselves, however, are mounted upon 3-in. risers which may be portable and moved about from one position to another by means of a quick coupling at the foot. The advantages of this system include the following: 1. 2. 3.

No interference from the vegetation in the distribution of the water Little interference with other field operations Fairly high coefficient of uniformity of water application, if several guns are used simultaneously with the correct spacing 4. Simple to operate 5. Low labor requirements 6. No land lost from cultivation because of closely spaced supply canals and drainage ditches 7. No problem of structures to cross canals 8. Suitable for rolling topography and for irrigation of areas lying at elevations higher than the point of supply of the water 9. Very low maintenance and repair requirements 10. No land leveling required 11. Nighttime operations possible 12. Low vo/umesof water can be applied to light soils with low water holding capacity and moderately low rates of irrigation can be provided for heavy soils with low rates of infiltration Among the disadvantages of the use of sprinkler guns are the following: 1. 2. 3. 4. 5. 6.

Initial cost of the equipment may be higher High energy requirements to provide the necessary working pressures Not suitable when wind velocities are high Some evaporation losses from the wet foliage Large discharges of water required Hazard of splash erosion and crust formation when the guns are used on soil before adequate vegetative cover is developed

Center-Pivot System This is a comparatively recent development which will become increasingly important for the irrigation of large tracts with a minimum of labor. It is well adapted to cane plantations. The irrigation is done with rotating sprinklers mounted on a long line which moves radially around a central pivot. The line is supported high above the ground by a light truss construction between a series of towers. Each tower is mounted on wheels and is equipped with an electric motor to make it self-propelled. The central pivot is fixed to a stationary base. It contains the central control unit which regulates the speed of the motors on the individual towers, as well as the rate of flow of the

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FIGURE 3. Central pivot irrigation system. (From Farbman, M., Center Pivot Sprinkler System and its Economics in Israel, M.Sc. thesis, Technion, Israel Institute of Technology, 1978. With permission.)

water. It is connected to the water supply which may be a ditch, a well or a pipeline (see Figures 3 and 4). The length of the line may vary from 75 to 750 m (250 to 2500 ft) with tower spacing between 30 to 60 m (100 to 200 ft). There may be as many as 20 towers on a line. The tower motors may be operated by electricity or by water pressure, with a maximum speed of 480 m/hr (0.30 mi/hr). The clear height under the sprinkler line (at the lowest point) may vary from 1.5 to 3.0 m and is therefore suitable for sugar cane. Higher clearances can be designed if necessary. The line can traverse rolling topography with slopes up to 30%. The system may use discharges of up to 800 mVhr, requiring a pressure from 1.0 to 7.5 atm (15 to 110 p.s.L). The time required to complete one rotation may vary from 12 to 20 hr. The irrigated area is a circle of radius equal to the length of the line. Some systems have an extension pipe to irrigate the corner areas outside the circle. The rate of application of the irrigation and the total volume of water can be varied over a wide range by changing the hydraulic discharge and the rate of rotation of the line, as well as the total time of operation at a given position. In this way the various requirements of the soil and crop can be met. This is especially valuable in the case of sugar cane, where different rates and volumes of irrigation water are required at different stages of the plant growth. Fixed sprinklers Fixed drip irrigation Long center-pivot (fixed) Short center-pivot (fixed) Short center-pivot (two positions)

100% 345% 68% 136% 100%

The hand-labor requirements for these systems, including installation at the beginning of the irrigation season and dismantling at the end, have the following ratios: Fixed sprinklers Fixed drip irrigation Long center-pivot (fixed) Short center-pivot (fixed) Short center-pivot (two positions)

100% 312% 14% 25% 78%

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FIGURE 4.

127

Central pivot irrigation equipment.

It can be seen that in general the long center-pivot system has lower total costs than the other systems and is very much lower in labor requirements. Among the disadvantages of the center-pivot system are the following: 1. 2. 3, 4,

Large component for diesel fuel in the operating costs Corners outside the circle require special irrigation equipment Economical primarily for large fields Requires higher manpower skills for maintenance

Linear Irrigation The linear system is another recent development which, like the center-pivot, will have increasing importance in sugar cane irrigation. It consists of a central supply unit which is mobile and straddles an irrigation canal. (An alternative to the central supply canal is the use of a flexible pressure supply pipe.) Extending at right angles to the canal in either or both directions is a single long lateral, supported at regular intervals by self-propelled towers similar to those used in the center-pivot system. On this line are mounted rotating sprinklers. The entire system moves in the direction of the canal and irrigates a strip the width of the lateral line. The lateral may be as long as 800 m (0.5 mi) and the forward motion may be as long as 2500 m (1.5 mi). The vertical clearance under the lateral is 3.0 m, and the lines can handle up to 450 mVhr. With an application of 10 mm/hr a system of this type can cover from 2.0 to 3.5 ha (5 to 9 acres)/hr. The advantages of this system include the following: 1. 2. 3. 4. 5.

Flexibility in rate of irrigation application and total amount of water applied High coefficient of uniformity Very low labor requirements Noninterference of irrigation lines and sprinklers with other field operations Suitable for rectangular fields

Among the disadvantages are the following: 1. 2. 3. 4.

Economical primarily for large fields Large component for diesel fuel in the operating costs Limited to fairly level topography Requires higher manpower skills for maintenance

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Drip Irrigation In recent years some application has been made of drip irrigation to sugar cane, especially in Hawaii. The principles of drip irrigation are fully described in Volume 1 and will not be repeated here. There are several principal advantages of this method in the irrigation of cane. The first is water economy. As there is no loss incurred by evaporation of falling drops in the air, nor by evaporation from the large surface area of the wetted foliage, the proportion of the water effectively applied to the root zone is higher than in all types of sprinkler systems. Drip irrigation is also more economical of water than the furrow system, because of the much greater uniformity of application. In regions where water is scarce and very expensive, drippers should be given serious consideration. The second advantage of the drip system is the fact that under almost continuous operation of the drippers the soil moisture content is kept very high. It can be seen from Figure 1 that the rate of photosynthesis and of dewlap growth are highest when the moisture stress is very low — less than 0.5 atm. This may account for the fact that some of the preliminary results obtained with drip irrigation give yields higher than those obtained by conventional methods in which the moisture stress may be allowed to increase to 2 atm or more before the next irrigation. Experimental data must be collected in each region in order to determine whether the increases in yield are sufficient to justify the greater expense involved in installing drip irrigation. A third advantage of the drip system is the low operating pressure. This greatly reduces the energy or fuel requirements as compared to the sprinkler guns or the center-pivot system. Among the disadvantages of the drip system for large areas of sugar cane is primarily the high cost. Studies made in various countries have shown the drip system to be substantially more expensive than the conventional portable sprinkler system and somewhat more expensive than fixed sprinkler installations. One should bear in mind that such comparative cost studies are strongly influenced by the prices of energy, labor, water, customs duties on imports, etc. In some areas the cost of drip may be as much as three times that of other systems. Hence, local cost studies must be made before a decision on drip irrigation can be taken. In areas where the water has a large amount of dissolved minerals, this may cause precipitation and clogging of the orifices, which, on a large cane plantation, would be very troublesome to clean out. In addition, the presence of drip lines along every row of cane may interfere with other field operations and be subject to damage during cutting and burning operations. In summary, the use of drip irrigation on sugar cane should be given serious consideration after all of the yield responses, local costs, and other parameters have been carefully studied. SUGAR BEETS Introduction The sugar beet (Beta vulgaris) is a cultivated descendant of the wild sea beet (B. maritima), which is an annual crop growing in the regions of the Mediterranean and Asia Minor. Unlike its ancestor, the sugar beet has erect leaves which do not interfere with one another. This increases the exposure to sunlight and photosynthesis is consequently greater. The crop has been grown for a long time in the northern, rainfed countries, as it can tolerate temperatures as low as 10°C during the growing season. In recent years, however, it has been grown increasingly in warmer, dryer regions with irrigation, since optimum sugar yields are obtained with night temperatures around 15 to 20°C and day temperatures from 20 to 22°. Sugar beets also have a relatively high tolerance to salinity. For these reasons the world distribution of the crop is very wide. At present about 9.5 million ha of sugar beets are grown, yielding close to 300 million tons of beets and providing about 40% of the world sugar supply.12

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FIGURE 5. Development of sugar beet roots. (From Bielorai, H. and Rubin, I., Irrigation Experiments on Sugar Beets in the Northern Negev (transl.), preliminary report, Volcani Inst. Agric. Res., 1957. With permission.)

Stages of Growth and Root System of Beets Three growth stages are generally recognized in the beet grown for sugar. The first is from the time of sowing to emergence. This may vary from 25 to 35 days, depending upon temperatures and other conditions. The second period is from emergence to the point of constant growth. During this period, lasting from 75 to 115 days, the leaf surface develops more rapidly than the roots. In the third period, the rate of growth is more constant, and strong roots develop as well as a large canopy of leaves. This period may extend from 40 to 50 days. The total growing season is thus from 140 to 200 days. The root development on a deep, well-drained loess soil (Israel) was measured by Bielorai and Rubin 5 and is shown in Figure 5. It will be seen that the developed plant has, in addition to the strong, deep tap root, a set of well-branched lateral roots which fill the upper 35 cm of the soil, and extend to a radius of about 50 cm. It was found that plants which were irrigated in the spring extracted 60 to 70% of their water from the upper 60 cm (2 ft) of the soil layer and an additional 10 to 20% from the 60- to 90-cm layer. In areas of high water table, or in soil profiles having a strata of low permeability, the root development will be correspondingly limited. The process of photosynthesis results in the formation of sugar in the leaves of the plant. Some of this is used by the plant in its metabolic processes and any surplus sugar is stored in the fleshy part of the root. The formation of sugar during the period of maximum growth is encouraged by bright sunny days, which increase photosynthesis, and cool nights, which reduce the moisture lost to the plant in transpiration. When the period of harvesting approaches, those cultural practices should be avoided which encourage leaf growth. Consequently, the application of nitrogen fertilizer and irrigation should not be done when night temperatures rise above the optimum for sugar production. This is the key to high yields of irrigated sugar beets and it helps to explain the results obtained in a great many irrigation and fertilizer trials in different countries. Water Requirements and Irrigation Regime of Sugar Beets Based upon the method described in Volume 1, the crop factor, K c , is the ratio of the water requirement of the crop in question and the water requirement of a full cover

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of grass. Estimated values for K c of sugarbeets are as follows: for the second stage of growth described above, the Kc varies from 1,05 to 1.20, with the higher value applied to conditions of lower humidity and greater windspeeds. In the last stage of growth, the K c values begin around 1.0 and reduce gradually to 0.6. No irrigation is to be applied in the last month before harvest. In absolute terms, the amount of water required to produce a crop of sugar beets ranges from 450 to 850 mm (18 to 34 in.)- For the method of converting the K c values to actual quantities of irrigation, see the chapter on "Water Requirements of Crops*' in Volume 1. Studies in Israel A classic study of the optimum irrigation of sugar beets was done in Israel by Bielorai and Rubin 5 under conditions of very little rainfall, strong sunlight, high daytime temperatures, and loess soil. Seven different irrigation regimes were tested, ranging from two to eight per season. It can be seen from Figure 6 that the driest treatment resulted in the highest concentration of sugar in the roots. A large number of irrigations actually caused a decrease in the percentage of sugar in the roots in the last month of the growing season. In Figure 7, the results of two seasons of irrigation are combined and the relative yields of roots and of sugar, expressed in terms of percentages of the maximum yields, are plotted against the dose of effective water (irrigation plus effective rainfall). It can be seen that the highest yields of beet roots were obtained in the vicinity of 700 mm (28 in.) of water applied. However, the yields of sugar were also at a maximum at about 700 mm of water application, but were not appreciably less at 500 mm (20 in.) of water. From the point of view of water economy, it was found that the treatment with only three irrigations was so close to the optimum with respect to sugar production that additional irrigations were not justified. This conclusion is of course relevant for the conditions of the experiment, where water is generally scarce and the cost of labor for irrigation is high. Irrigation trials were conducted in three other regions in Israel with more or less similar results. In most of the trials the cessation of irrigation in the last 30 days before harvest did not lower the yield of sugar. The Israel studies seem to confirm the recommendations of FAO (Paper No. 33)12 for the most effective use of irrigation water which are as follows: When available water resources are limited, and when maximum overall production is aimed at, water supply should be directed toward expanding the area under irrigation rather than concentrating the supply over a limited area to meet maximum water requirements over the total growing period. This is because there is an increase in the efficiency of water utilization for both roots and sugar yield when the water supply is reduced so that yields decrease less than proportionately with the reduction in water supply provided the growing environment during the later part of the growing period is favorable to sugar storage.

Studies in the U.S. Several detailed studies of sugar beet irrigation have been reported in the U.S. A typical one was carried out in Montana (Larson and Johnson)17 and will be summarized here. Three irrigation regimes were followed, keeping the minimum soil moisture percentage at either high, medium, or low level. This was tried on an area where the water table was below 10 ft in depth, and again on an area where the water table remained between 4 to 4.5 ft. The results are summarized in Table 2. It should be noted that the date of harvest was September 28. In the trials carried out on an area of very low water table, the treatment with higher minimum moisture levels achieved by smaller, more frequent irrigations gave a significantly higher yield of roots. There were only small differences between the sugar concentration of the wettest and the driest treatment. In the case of high water table conditions, somewhat higher-root yields were obtained with the medium moisture treatment, but the sugar concentrations in all three treatments were significantly lower than in all treatments

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FIGURE 6. Sugar concentration as a function of irrigation. (From Bielorai, H. and Rubin, I., Irrigation Experiments on Sugar Beets in the Northern Negev (transl.), preliminary report, Volcani Inst. Agric. Res., 1957. With permission.)

FIGURE 7. Relative root and sugar yields as a function of water applied. (From Bielorai, H. and Rubin, I., Irrigation Experiments on Sugar Beets in the Northern Negev (transl.), preliminary report, Volcani Inst. Agric. Res., 1957. With permission.)

of the low water table trials. This is probably the result of high soil moisture content during the last month before harvesting, since the irrigation regime was incapable of controlling the availability of the moisture. In these same trials close attention was paid to the extraction of moisture from different depths of the soil under the various conditions. The results are summarized in Figure 8. It can be seen that in general, under a regime of high moisture level, most of the moisture was extracted from the upper foot (30 cm) of the soil. With the drier treatments the second and third foot layers contributed more, but very little moisture was extracted from the layer between 3 and 4 ft in depth. The rate of moisture extraction ranged from 0.075 in./day, or 1.9 mm/day, at the beginning of the growing season to 0.26 in./day, or 6.6 mm/day, at the peak of the season with the high moisture treatment. With the low moisture treatment (larger, less frequent irrigations) the peak

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Technology

Table 2 YIELDS OF SUGAR BEET ROOTS AND TOPS AND SUCROSE PERCENTAGE AS AFFECTED BY SOIL MOISTURE LEVEL AND DATA RELATIVE TO THE IRRIGATION TREATMENT Approximate % available water removed from root zone Moisture prior to Number of level irrigation irrigations

Yield (ton/ ha) Mean inches Sucrose water applied Sucrose produced Dates of irrigation per irrigation Roots Tops (%) (ton/ha)

Fly Creek Clay Loam (Water Table 10 Ft in Depth) High

43

8

Medium

75

5

Low

95

1

July 2,9,14,20,28; Aug. 14,20; Sept. 11 July 7, 15; Aug. 5,24; Sept. 12 July 30

2.5

53.2

37.3

14.8

7.87

3.1

50.0

38.2

14.0

7.00

5.1

38.4

33.4

14.5

5.57

Pryor Silty Clay (Water Table 4 to 4.5 Ft in Depth) High

54

7

Medium

66

4

°

0

Low

June 30; July9,15,21,31; Aug. 12,25 July 6,18; Aug. 6,28

2.5

52.0

56.1

13.3

6.92

3,7

53.4

66.4

12.5

6.68

—

45.7

67.0

11.8

5.39

This treatment was not irrigated because stored soil moisture and rain, together with subirrigation from ground water, kept available moisture in the root zone throughout the season. The percent of available moisture varied greatly and thus no figure is listed.

daily demand reached 0.30 in./day or 7.6 mm/day. The total water consumption for the season ranged from 23.4 in. (about 600 mm) for the wet treatment to 19.0 in. (about 480 mm) for the dry treatment. Water Quality The problems of irrigation water quality and soil salinity are discussed thoroughly in Volume 1, chapter on "Soil Salinity and Water Quality". In Table 5 of that chapter the tolerance of various crops for different levels of soil and water salinity are given. For sugar beets, it is seen that the reductions in yield to be expected from different levels of salinity of the soil saturation extract (ECe) and the irrigation water (ECw) expressed in millimhos per centimeter are as follows: Yield reduction W

ECe

ECw

0 10 25 50 Maximum

7.0 8.7 11.0 13.7 24.0

4.7 5.8 7.5 8.7

From this it is seen that the sugar beet has a relatively high tolerance for saline water.

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FIGURE 8. Consumptive use of water by sugar beets at various soil depths as influenced by three soil moisture levels. (From Larson, W. E. and Johnson, W. B., Soil Sci. Soc. Proc.,275, 1955. With permission.)

If the ECw is around 5 mmhos/cm the yield is hardly affected. This represents an order of magnitude of around 2000 ppm of total dissolved salts. It must be remembered, however, that during the germination period the tolerance is lower and the ECe of the soil extract should not exceed 3 mmhos/cm. Sugar beets are also tolerant to exchangeable sodium and start to show signs of sodium toxicity at ESP (exchangeable sodium percentage) in the range of 40 to 60. The crop is also tolerant to boron, with a permissible level approaching 4.0 mg/i. Irrigation Methods for Sugar Beets The traditional method for irrigation of sugar beets is by furrows. It has the following advantages: 1. 2. 3. 4. 5.

Suitable for a row crop The salinity problems created by furrow irrigation are less critical because of the higher tolerance of sugar beets Relatively low financial investment Simple to operate Low energy requirements

The disadvantages are as follows: 1. 2. 3. 4. 5. 6.

Lower efficiency of water use Less uniform distribution of water Higher labor costs Loss of land for supply canals and drainage ditches Land leveling required on irregular topography Only areas below the supply canal can be irrigated

Because of the above disadvantages of the furrow method, sprinkler irrigation has become more popular for sugar beets. It requires a larger investment in equipment,

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but this may be reduced considerably by the use of relatively long, portable laterals which can be shifted from place to place. The labor costs can also be reduced by the use of laterals mounted on wheels or small slides and dragged to the new position by a tractor. The sprinkling equipment can then be completely removed from the field a month before harvesting, and the mechanical harvest can be carried out with no interference. A disadvantage of the sprinkler system, however, is the cost of energy for developing the required pressure. Recently some sugar beet fields have been irrigated by the drip method. The principal advantages of this method are 1.

2. 3. 4.

Higher yields. As was shown by the various research studies, the yields of sugar beets are higher when the depletion of soil moisture between irrigations is smaller. With the drip system, the soil moisture can be kept close to field capacity at all times. This will result in higher yields provided that the other agricultural requirements, such as soil fertility, plant protection, etc. are satisfied. Water economy. A larger proportion of the applied water goes directly to the zone of active roots. Consequently, the yield per unit of water applied is higher than in the other methods of irrigation. Energy economy. Since the drip system operates at pressures usually not exceeding 1.0 atm, less energy is required than in the sprinkler system. Low labor requirements. Labor requirements for operation are low once the system is installed.

These advantages must be balanced against the first costs which are usually somewhat higher.

REFERENCES 1. Ashton, F. M., Effects of a series of cycles of alternating low and high soil water contents on the rate of apparent photosynthesis in sugar cane, Plant P/jys/o/.,31(4), 266, 1956. 2. Anon., Hawaii, Sugar Plant. Assoc. Exp. Stn. Annu. Rep., 1960. 3. Arnon, I., Crop Production in Dry Regions, Vol. 2, Leonard Hill, London, 1972. 4. Barnes, A. C., The sugar cane, in World Crops Books, Interscience, New York, 1964. 5. Bielorai, H. and Rubin, I., Irrigation Experiments on Sugar Beets in the Northern Negev, (transl.), preliminary report, Volcani Inst. Agric. Res., 1957. 6. Cowan, I. R. and Innes, R. E., Meteorology, Evaporation and the Water Requirements of Sugar Cane, Meet. Br. W. Indies Sugar Technol., 1955. 7. Clements, H. F., Shigeura, G., and Akamine, E. K., Ripening sugar cane, Hawaii Agric. Exp. Stn. Res. Rep. 120, 1948. 8. Cornelison, A. H. and Humbert, R. P., Irrigation interval control in the Hawaiian sugar industry, Hawaiian Plant. Kec.,55(4), 331, 1960. 8a. Doorenboos, J. and Kassam, A. H., Yield Response to Water, Irrigation and Drainage Paper No. 33, Food and Agriculture Organization, Rome, 1979. 9. Farbman, M., Center Pivot Sprinkler System and its Economics in Israel, M.Sc. thesis, Technion, Israel Institute of Technology, 1978. 10. Food and Agriculture Organization, Crop Water Requirements, Irrigation and Drainage Paper No. 24, Rome, 1975. 11. Food and Agriculture Organization, Water Quality for Agriculture, Irrigation and Drainage Paper No. 29, Rome, 1976. 12. Food and Agriculture Organization, Yield Responses to Water, Irrigation and Drainage Paper No. 33, Rome, 1979.

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13. Humbert, R. P., The Growing of Sugar Cane, revised ed., Elsevier, Amsterdam, 1968. 14. James, D. W., Growing Sugar Beets for Maximum Sugar Production, Wash. Agric. Exp. Stn., Washington State University, Pullman, 1966. 15. King, N. J., Mungomery, R. W., and Hughs, C. G., Manual of Cane Growing, Elsevier, New York, 1965. 16. Kramer, P. J., Plant and Soil Water Relationships, McGraw-Hill, New York, 1949. 17. Larson, W. E. and Johnson, W. B., The effect of soil moisture on the yield, consumptive use of water and root development of sugar beets, Soil Sci. Soc. Am., Proc., 19, 275, 1955. 18. Mauritius Sugar Industry Research Institute, annu. rep., 1962 to 1964. 19. Sugar Manufacturers Association of Jamaica, annu. rep., 1955 and 1956.

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IRRIGATION OF OIL CROPS Shaul Feldman PEANUTS Introduction In the world, peanuts (also known as groundnuts) are generally spoken of as the poor man's crop because of their high nutritive value. They have an oil content varying from 48 to 51% and contain about 25% protein, which makes the crop important in protein-deficient countries throughout the world. Peanuts are partly irrigated in the U.S., where they are produced under rainfall conditions or fully irrigated in arid countries such as Israel and India where there is no rainfall during the growing season. In most of the underdeveloped countries peanuts do not receive supplemental irrigation, although they could benefit from it. Root Characteristics The root system in peanuts consists of a tap root with many laterals and adventitious roots from the hypocotyl and areal branches.310 The root system may penetrate to a depth of 3 to 6 ft (1 to 2 m) in cultivated soils. This extensive root system and its capacity to absorb water can be partly responsible for the lack of widespread irrigation of peanuts in those parts of the U.S. where some rainfall is present during the growing season.30 Depth of roots and thoroughness of root development are important factors in determining the quantity of water which may be extracted from the soil before irrigation is required. The fairly extensive peanut root system is especially important when the rainfall distribution pattern is erratic. Peanut Irrigation Investigations U.S. Studies Matlock et al.15 carried out peanut irrigation trials at Stillwater, Okla. from 1956 to 1959, with the Argentine variety, with the results as shown in Table 1. The average percentage of sound, mature nuts was 56.5 under irrigation as compared to 52.5 when not irrigated. However, the average protein content of the nuts was 29.7% as compared to 32.5% without irrigation. A further effect of the irrigation was to decrease the length, diameter, and thickness of the pods, and to decrease the pressure required for cracking them. It is clearly seen that under the optimum treatment (irrigation when moisture tension = 2 atm) the increase in yield over no-irrigation is 53%, which greatly offsets the small reduction in the protein content caused by irrigation. Choy,3 in Oklahoma, investigated the effects over 6 years of various plant densities with and without irrigation on the yield and quality of peanuts and the effects of various row spacings and orientations on the evapotranspiration. The highest yields were obtained with a between-row spacing of 25 cm. The optimum within-row spacing varied with the years but was in the range of two to four plants per 30 cm (1 ft). Irrigation increased the yield and quality. Pallas and Stansell18 in Tifton, Ga. made field trials on three varieties of peanuts with six irrigation regimes. The wettest regimes were 530 to 590 mm of water (21 to 23 in.) and the driest were 220 to 230 mm (8.6 to 9.0 in.). The results were obtained as shown in Table 2. Water use efficiency was inversely correlated with photosynthetic efficiency. The same investigators, Stansell and Pallas23 subjected Florunner peanuts to drought

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CRC Handbook of Irrigation Technology Table 1 IRRIGATION OF PEANUTS IN OKLAHOMA Irrigation regime

Average yields of clean, air-dry unshelled nuts (kg/ha)

No irrigation Irrigation when moisture tension in 15- to 30-cm soil layer (6 to 12 in.) = 6 atm (two)irrigations of 76 mm each, or 3 in.) Irrigation when moisture tension = 2 atm (three irrigations of 76 mm each) Irrigation when moisture tension = 1 atm (four irrigations of 76 mm each)

1860 2530 2850 2800

Table 2 IRRIGATION OF PEANUTS IN GEORGIA Yields (t/ha of dry matter) Wettest treatment

Driest treatment

Photosynthetic efficiency (%)

Variety

Below ground

Above ground

Below ground

Above ground

Wettest

Driest

Florigiant Florunner Tifspan

5.8 5.7 4.7

6.4 5.3 4.6

1.7 2.7 2.7

5.4 4.4 3.4

2.2 2.1 2.0

1.2 1.3 1.3

stress periods of 35 day duration at ages 36 to 70, 71 to 105, and 106 to 140 days. In addition, 70-day droughts were imposed at 36 to 105 and 71 to 140 days of age. Yield and quality responses were compared to groundnuts grown with adequate water throughout the season in Georgia. Pod yields from all treatments were significantly different from each other, ranging from 5165 kg/ha for the no-drought treatment to 1387 kg/ha for the 36- to 105-day drought treatment. As indicated by the pod yield, the 35-day drought spanning the age bracket of 71 to 105 days was more damaging than 35 days drought at 36 to 70 or 106 to 140 days of age. The 70-day drought beginning at 36 days of age reduced SMK (sound mature kernel) percentage to only 34%, while pods from the 70-day drought treatment starting at 71 days of age graded 69% SMK. The SMK percentage from the 106- to 140-day drought treatment was 78%, not significantly different from the no-drought treatment. Percentage of other kernels (immature, shrivels, etc.) was increased by drought from 36 to 105 days but not by drought from 71 to 140 days. Barkman et al.,2 comparing data developed from the late season drought of 1976 in Alabama with the early season drought of 1977, demonstrated the role of irrigation water in intensifying groundnut disease, as well as the time of water application in relationship to disease severity. In 1976, peanut leafspot was increased slightly when plots maintained under a standard 14-day chlorothalmil program were compared for disease severity. However, when irrigation water was applied early in the season (1977), leafspot-induced defoliation was 50% greater than in the nonirrigated control. Results from 1977 indicated a greater effect of irrigation on end-of-season leafspot levels, partially because the irrigation water was applied earlier, allowing inoculum potential to reach a high level much earlier. The high level of leafspot inoculum found early in the season expressed itself as much higher levels of defoliation late in the season. Irrigation was consistently correlated with increased damage from Sclerotium rolfsii.

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Table 3 IRRIGATION OF PEANUTS IN BHAVANISAGAR Percentage of field capacity at time of irrigation

Yield of pods (kg/ha)

40 60 80

2761 3221 2800

Table 4 MULCHING OF PEANUTS IN BHAVANISAGAR Type of mulch

Yield of pods (kg/ha)

No mulch Rice straw Glyricidia leaves

3086 3265 3291

Summary of the U.S. Studies The studies of peanut irrigation in the U.S. fall generally into two groups. The first includes work done in Alabama, Georgia, and other parts of the southeast. These are regions of ample rainfall in most of the years, with occasional periods of mild or severe drought. As might be expected, yield responses to irrigation are only significant in the years of seasonal rainfall deficiency. Consequently, irrigation may be recommended as a supplementary measure only. The second group represents studies done in areas of the southwest, which are notably arid or semiarid during the growing season, such as in Oklahoma. The yield response to irrigation of peanuts is much more significant here and irrigation must be thought of as a regular practice rather than supplementary. It is noteworthy that the aggravation of the disease problem caused by irrigation is more serious in the humid regions. The economics of irrigating peanuts are different in these two types of regions. In the humid region, where supplementary irrigation is required from time to time, only a lower investment in equipment could be tolerated. Consequently the use of a portable sprinkler system is advisable, with a relatively smaller amount of pipes moved rapidly. A good drainage system is also needed in case a sudden rain comes shortly after irrigating a large cultivated area. In the semiarid region it would be economically more justified to install a more permanent system, with a network of fixed-in-place supply pipes, and more portable laterals and sprinkler heads. Likewise, for furrow irrigation, it would pay to install a permanent network of supply canals, turnout structures, and appurtenances. Indian Studies Mohan 16 in Bhavanisagar studied the yield response of peanuts when irrigated at different levels of soil moisture. The results are shown in Table 3. This indicates that the optimum time for irrigation is when the soil moisture falls to 609/o of the readily available moisture at field capacity. Both the drier and the wetter regimes gave significantly lower yields. The same investigator studied the effect of mulching (applied 30 days after sowing) on peanut pod yields with the results as shown in Table 4. The moisture conserving effect of either type of mulch increased the yields by about 6%.

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CRC Handbook of Irrigation Technology Table 5 PEANUT IRRIGATION STUDIES IN MADRAS Percent of available moisture at time of irrigation

Yield of pods (kg/ha)

0 20 40 60

2190 2830 3030 3240

Table 6 YIELD OF GROUNDNUT PODS IN HYDERABAD Yield of pods (kg/ha) Irrigation at depletion of available moisture at (%)

Okg (P/ha)

21.8kg (P/ha)

43.6kg (P/ha)

Mean

25 50 75 Mean for P levels

4680 3932 3343 3985

4365 4639 3685 4230

4320 4372 3161 3951

4455 4314 3396 4055

All et al.1 in Madras studied the effect of different degrees of moisture stress on the yield of peanuts grown in the winter (rabi). They irrigated at different levels of available moisture in the top 30 cm of the soil, with the resulting yields as shown in Table 5. Because of the increased yields under irrigation, it can be expected to obtain a significant response to the addition of fertilizer. The same investigators found this to be true in 1 out of 3 years, with the application of 12.6 tons/ha of farmyard manure, in addition to a basal dressing of 33.6 kg/ha of N, 33.6 kg/ha of P2O5, and 50.5 kg/ha ofK 2 O. Sandhu et al., 24 in trials at Hissar on sandy loam, studied the effects of irrigation and fertilization with the following results: with groundnut cv. (cultivar) C501 given 15 kg N and 15 to 60 kg P 2 O 5 per hectare, two irrigations, one at flowering and the other at fruiting, in addition to the two normal irrigations given in the first and third months after sowing, gave 50.6 and 33.1% higher yields of unshelled nuts than no irrigation and one irrigation at flowering, respectively. The total oil yield was increased by 292 kg and 91 kg/ha with two and one additional irrigations, respectively. At Ludbiana, Cheema et al.6 studied the effects of irrigation during two Kharif (summer monsoon) seasons. They found no significant differences in the yields of peanuts when given up to ten irrigations. Obviously irrigation is not necessary during seasons of well-distributed rainfall. Narasmam et al.17 in the Hyderabad region studied the combined effects of irrigation phosphorous and fertilization on peanuts with the results as shown in Table 6. The shelling percentages in all the treatments were fairly constant (80 to 81 %) as was the percentage of oil in the seeds (49 to 51%). It can be seen that the average yields for all the different phosphorous treatments was 31% higher under irrigation at the 25% moisture depletion as compared to the 75% moisture depletion regime. It says, therefore, to irrigate the groundnuts more frequently. Raju 20 in the Tirupati region tested the response to plant spacings, phosphorous fertilization, and moisture stress. His findings were as follows: groundnut cv. TMV2 grown at between-plant spacing of 5, 10, 15 cm in rows 30 cm apart, given 0 to 80 kg

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P2O5 per hectare and irrigated at the depletion of 25, 50, or 75% available soil moisture (ASM) gave the highest pod yields when grown at a spacing of 30 x 10 cm, given 40 kg P2O5 per hectare and irrigated at 25% ASM. T'emgire29 in the Poona region studied the effect of irrigation intervals on shelling percentage and on the 1000 seed weight. His results were as follows: in trials in 1967 to 1969 with groundnuts, the values for shelling percentage and 1000-seed weight were higher on plots irrigated at 21-day intervals than on those given one irrigation at 35 to 70 days after sowing or two irrigations at 35 and 70 days; seed soil content was not significantly affected. There was little difference in quality characteristics between irrigation levels of 5 and 7.5 cm. Reddy et al.2! of the Mysore district grew peanuts on a red sandy loam during two successive wet seasons. The varieties grown were cv. BH 8-18, TMV2, and S230. The variables studied were variety, plant spacings, row spacings, moisture stress, pod yields, number and weight of mature pods per plant, and consumptive use of water. In both years BH 8-18 gave the highest average pod yields of 2.02 t/ha compared with 1.6 and 1.1 t/ha with TMV2 and S230, respectively. Irrigation when the soil moisture content in the top 30 cm was depleted by 50% increased pod yield from 1.45 t/ha under rainfed conditions to 1.7 t/ha. Irrigation also increased the number and weight of mature pods per plant. Pod yield was not significantly affected by plant density. Consumptive use of water was 467, 444, and 417 mm with S230, BH 8-18, and TMV2, respectively, and was related to crop duration. Winter use efficiency was highest with BH 8-18. Consumptive use of water was highest with the 45-cm row spacing. Subramanian et al. 22 irrigated groundnuts in India at ratios of irrigation water to cumulative pan evaporation levels (IW/CPE) of 0.9 and 0.6. The irrigation applications were made at the following periods: (1) sowing to flowering (up to 30 days); (2) effective pegging (30 to 45 days); and (3) pod formation maturity (after 45 days). The highest yields of unshelled nuts, 2210 kg/ha, was obtained with irrigation at the IW/ CPE ratio of 0.6 during (1) and (2) and 0.9 during (3). This treatment also gave the highest water-use efficiency of 53 kg unshelled nuts per centimeter of water. Irrespective of other irrigation regimes during (1) and (2) irrigation at the IW/CPE ratio of 0.9 during (3) gave significantly higher yields than did irrigation at the IW/CPE ratio of 0.6. Groundnuts sown in February were given irrigations scheduled at 75, 100, 125, or 150% of the cumulative pan evaporation (CPE). The highest pod yields were obtained with irrigations scheduled at 75% CPE (Dhatonde7). Summary of the Indian Studies In India, the peanut generally receives some rainfall during the growing season, but due to the reported field results the peanut crop should be given supplemental irrigation when the available moisture in the 30-cm soil has been depleted by 30% in order to obtain maximum yields of high quality. Where rainfall has been ample no significant differences in the yields were obtained as expected. Far East Studies Chang, 5 in Formosa, studied the response by upland crops to irrigation during the winter and early spring dry season (where the annual rainfall is 2000 mm). Groundnut yields increased 20% after one irrigation of 70 mm, applied 80 days after sowing (autumn). A greater response was shown by upland rice. Su et al. 25 reported on irrigation results in the Tainan district in Formosa with the groundnut cv. Tainan No. 6 (Spanish type). The moisture absorption rate (defined as the amount absorbed in a 5-day period in relation to that absorbed in the whole growth period) was about 2% before flowering (1 to 30 days after sowing) and increased to 78% at pod development (60 days after sowing), a value which was maintained to maturity. Yields could be increased by

142

CRC Handbook of Irrigation Technology Table 7 IRRIGATION OF PEANUTS IN ISRAEL Irrigation treatment

Interval (days)

Pan coefficient

Water applied (mVha)

Average yields (kg/ha)

Low Intermediate

10 7 10 7 7 10

0.60 0.75 0.75 0.60 0.90 0.90

5140 6000 5840 5770 6560 6400

4040 4570 4600 4200 5290 4600

High

73 to 83% with irrigation. The period of greatest susceptibility to drought was at peak flowering (50 days after sowing), and the greatest yield with the minimum of irrigation was attained by applying 40 mm at this stage. Israel Studies In Israel, groundnuts are grown during the summer months when there is no rainfall. They are completely dependent upon irrigation. A number of important studies were made on irrigation, the results of which are briefly summarized below. Consumptive Use Goldberg et al.13 investigated the use of the U.S. Weather Bureau Class A evaporation pan data for the determination of water consumption and irrigation schedule of groundnuts growing in sandy soil. Two irrigation intervals, 7 and 10 days, were tested. Water use was determined with three pan coefficients of 0.6, 0.75, and 0.9. The treatments and the results are shown in Table 7. An irrigation interval of 7 days was significantly better than one of 10 days, according to the weight per thousand seeds and the percentage of full pods. Treatment no. 7/90 was the best, significantly, in pod filling and weight per 1000 seeds. Regarding percentage of export quality fruit it was found that a coefficient of 0.6 was significantly the worst, and that 7-day intervals were somewhat better than 10-day intervals. The highest export percentage was obtained in treatment no. 7/90. Irrigation Frequencies and Rates Feldman and Rubin, 10 investigating daily irrigation amounts and intervals, reported that groundnuts produced during the dry season on a loess type of soil should be irrigated every 10 days until 50 days after planting. The irrigation interval should then be increased to 15 days, with a total irrigation application of 7400 mVha (29 in.). Increasing the irrigation application beyond this did not have a significant effect on increasing yields. The irrigation intervals and amounts of water did not result in differences in the quality of the crop. Mantell and Goldin14 studied the response of groundnuts to five irrigation frequencies (10, 14, 21, 30 and 40 days) and to two sprinkler application intensities (6 and 12 mm/hr). The soil types were fine-textured sandy clay and clay. The optimum yield was obtained with five irrigations to a depth of 90 cm during the growing season at intervals of 30 days, and with a total seasonal water application of approximately 5500 mVha. The consumptive water use for the season was 670 mm from the 0- to 150-cm soil layer. There were indications that it may be sufficient to replenish at each irrigation the deficit from field capacity only in the 0- to 60-cm layer, provided the entire root zone is at field capacity at the beginning of the growing season. The effects of irrigation intensity on the yield of unshelled pods were not consistent and no differences between the two irrigations were reflected in shelling percentage, 1000-seed weight, or percentage of export quality yield.

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Feldman and Hartzook9 investigated the effect of two irrigation rates on the yield and quality of groundnuts under drip irrigation and sprinklers in a sandy soil. They found no significant differences in yield between a total irrigation of 4560 mVha with the drip method and 6700 mVha with sprinklers. The drip method significantly improved the 1000-seed weight but there was no response to pod weight and shelling percentage. Feldman and Shimshi8 investigated the effect on groundnuts of two drip irrigation levels and irrigation line spacings on a sandy soil. They found that the intervals did not influence yield or quality, while one lateral spaced between two groundnut rows significantly increased yield but not quality compared with one lateral per row of groundnuts. It is suggested that groundnuts may be irrigated with one line for two groundnut rows at 4-day intervals with a consequent saving of labor and irrigation lines. Sprinkler Intensities Gornat and Goldberg 11 grew Virginia Bunch groundnuts in containers filled with sand, sandy loam, or clay soil and irrigated the plants at sprinkler intensities of 3, 12, and 25 mm/hr. On the sandy loam, the yield obtained with the lowest sprinkler intensity was significantly higher than with the other two intensities. On the sand, sprinkler intensity had no significant effect, and on the clay soil, the yield obtained with the highest sprinkler intensity was significantly lower than that obtained with the other two. Summary of Israel Studies In Israel, the peanut crop must be completely irrigated due to no rainfall during the growing season. The crop should receive an average of a total of 7100 to 7500 mm. Depending upon the winter rainfall the preirrigation is applied. The recommended amounts of water applied by months are as follows: May — 1200 mVha; June — 1800 mVha; July — 2100 mVha; and August — 2100 mVha. SAFFLOWER Introduction Safflower (Carthamus tinctorius) belongs to the family Compositeae and originates in the Euphrates basin in the Middle East. It is an important oil crop in the Mediterranean basin, India, China, Japan, Mexico, and is also produced in the western half of the U.S. Due to the oil composition (3/4 either oleic or linoleic fatty acid) it is used as an edible oil in cooking, salads, margarines, and is used as an industrial oil for protective coatings, putties, caulks, and linoleums. The leaves are used for salads in India and safflower meal can be used to feed cattle as a source of protein. When planted in the rainy winter season and harvested at the end of May little or no irrigation is required. With irrigation, it is possible to produce safflower successfully in regions where the rainfall is inadequate at the time of planting, as in Mexico, and a supplemental irrigation is applied when deemed necessary. Plant Characteristics The root system of the safflower plant is deep and well developed. Maximum depths are as much as 3.5 m (11.5 ft), but most of the water is extracted in the first 1 to 2 m for the mature plant. The critical soil moisture level, below which growth and yield are adversely affected, is about 40% of the readily available soil moisture. The stages of growth of the safflower planted in the spring are approximately as follows: Establishment Early vegetative (rosette) development

4—10 25

days

144

CRC Handbook of Irrigation Technology Late vegetative (elongation and branching) Flowering Yield formation (seed filling) Ripening Total

60 30 25 10

160—154

days

From Doorenbos, J. and Kassam, A. H., Irrigation and Drainage Paper No. 33, Food and Agriculture Organization, Rome, 1979.

The growing period for autumn-planted varieties may be from 200 to 230 days. The crop is adapted to fertile, deep, and well-drained soils of medium texture. It is susceptible to excess humidity and fog, which induce head rot. Consequently it does very well under controlled irrigation in an arid or semiarid region. U.S. Studies Knowles44 gave an excellent review of the water relations in safflower production. It was reported that for a successful crop of safflower under California conditions, some 400 mm (16 in.) of soil moisture is required. For maximum crop yields about 675 mm (27 in.) of soil moisture will be required. Safflower is known to be drought resistant due to its strong tap root which will grow deeply on the soil moisture providing it is available. Safflower is considered more drought tolerant than small grains as the plant can extract moisture from 3- to 4-m depth in a loamy soil.44 Root growth is likely to be restricted by low soil temperatures at a depth of 3 to 4 m (reported in North Dakota by Hoag et al.41). Knowles510 reported that in the Great Plains of the U.S., if there is little accumulated soil moisture, safflower requires at least 275 mm (11 in.) of rainfall during the growing season to assure an average yield. Eric and French38 reported on safflower consumptive-use data over three growing seasons at Mesa, Ariz. The average seasonal moisture requirement was 1100 mm (44 in.). Peak use of over 12 mm (0.5 in.)/day was reached during the blossoming period. Bailey and Hoff 33 in New Mexico recommend using 1.5 m of water in order to obtain high safflower yields. A preplan! irrigation is recommended although the seed may be planted in dry soil and then irrigated. The periods of greatest water needs are during the budding, flowering, and seed development stages of growth. The last water application should be made about 2 weeks after flowering has ceased. Luebs et al.46 reported that consumptive use of moisture in the Antelope Valley of California was slightly less for a March 26 planting than for January and February plantings, but the total irrigation requirements were similar. Average consumptive use was 860 mm (34.4 in.). Moisture requirements for January 16 and February 13 plantings after the middle of May were similar. On the other hand, moisture use and development of safflower planted March 27 lagged behind. The peak average daily moisture use was 10 mm (0.4 in.). Moisture utilization efficiency for seed production was highest for safflower planted in January, and progressively decreased as planting was delayed. The results are presented in Tables 8 and 9. Jones43 reported that safflower responded to applied nitrogen at up to 513 kg/ha in nitrogen-deficient soil, but only when irrigated. Nitrogen increased the number of heads per plant, seed size in secondary heads, and number of seeds per head in tertiary heads. Fischer et al.39 made field trials in San Joaquin Valley, Calif, in which four irrigation treatments were used. The highest yield of safflower seed was obtained with a presowing irrigation of 457 mm (18 in.) plus irrigations of 203 mm (8 in.) at the bud and early-flowering stages, respectively. Evapotranspiration and irrigation results are presented in Tables 10 and 11. It is interesting to note that the highest yields per hectare were obtained with the wettest irrigation treatment. However, from the point of view of water use efficiency, the

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Table 8 PLANT HEIGHT, SEED YIELD, AND OIL CONTENT OF SAFFLOWER PLANTED AT DIFFERENT DATES IN 1961 TO 1962 IN CALIFORNIA Planting date

Plant height (in.)

Mean yield (kg/ha)

Mean oil content (%)

24

2390

34.3

21 19 9

2240 2550 720 410

35.1 35.9 35.1 NS

by frost 4710 4090 3360 2950 460

33.8 34.6 35.6 36.7 1.9

December 28, 1961 March 14, 1962 April3, 1962 April 28, 1962 L.S.D.-0.05

Nov. 30, 1962 Jan, 16, 1963 Feb. 13, 1963 March 27, 1963 April 27, 1963 L.S.D.-0.05

Planting destroyed 32 31 23 17

" L.S.D. = level of significant difference (%).

Table 9 EFFECT OF DATE OF PLANTING ON THE CONSUMPTIVE USE OF WATER BY SAFFLOWER IN CALIFORNIA Planting date January 16 February 12 March 27

(mm)

Irrigation (mm)

Net depletion of soil moisture (mm)

Total use (mm)

Seed yield (kg/ha)

850 600 425

200 145 212

200 215 187

900 887 890

4100 1860 1510

Rainfall

highest yield per hectare per millimeter of water applied was obtained with the driest irrigation treatment. This treatment also had the lowest rate of evapotranspiration. The choice of optimum irrigation regime depends upon the relative value of a kilogram of safflower seed, as compared to a millimeter of irrigation water. If the value of the seed is high, and the cost of water low, then treatment no. 2 should be followed to maximize crop production. If the cost of water saved under treatment no. 4 is worth more than the value of 1400 kg of safflower, then this is the optimum treatment. In almost all cases, however, costs will favor treatment no. 2. Eric and French,37 in Arizona, gave three to nine applications to eight irrigation treatments of fall-planted safflower when 69 to 72% of the available water in the top 120 cm (4 ft.) of soil was depleted. Five irrigation cutoff dates were compounded on the soil moisture depletion treatments, ranging from 3 weeks before first blossoming until harvest. The yield of safflower seed increased with each increment of irrigation water to a maximum yield obtained with seven irrigations given until the last blossoms opened (3961 kg/ha). Consumptive use for this treatment was 1070 mm (42 in.) of water. When the last irrigation was given at the first flowering date, seed yield was reduced over 800 kg/ha. Giving the last irrigation about 10 days before blossoming reduced yields by nearly one half. Weight per seed, oil content, and seeds per head

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CRC Handbook of Irrigation Technology Table 10 EFFECT OF IRRIGATION ON SAFFLOWER YIELDS Crop irrigation (mm) Treatment number

Preirrication October 63 (mm)

1 2 3 4

762 457 457 406

AprilH

May 28

203

203

178 —

Yields (kg/ha)

Water-use efficiency (kg/ha/mm)

2740 b 3450 a 2810b 2050 c

3.6 4.0 4,4 5.0

Note: Yields having the same letters are not significantly different at the 1 ability level.

prob-

Table 11 CALCULATION OF EVAPOTRANSPIRATION FOR VARIOUS IRRIGATION TREATMENTS IN SAN JOAQUIN VALLEY, CALIF.

Number

Total water applied

Calculated evapotranspiration (mm)

1 2 3 4

762 863 635 406

567.5 772.5 557.5 365.0

Ratio of E.T. to total water applied

Water leached beyond 3 m after preirrigation

Water remaining in soil profile after harvest

W

W

W

74.4 89.6 87.8 89.9

24.8 1.3 5.0 5.9

6.8 6,4 4.9

Table 12 YIELDS OF SAFFLOWER PER UNIT VOLUME OF WATER FOR DIFFERENT IRRIGATION REGIMES IN ARIZONA Number of irrigations

Yield (kg/ha)

Consumptive use (mm)

Water (kg/mm)

9 7 8 6 5 4 4 3

4056 a 3961 a 3953 a 3317b 2930 b 2220 c 2011 c 1819c

1340 1070 1270

3.03 3.70 3.11 3.38 3.49 2.92 2.68 3.08

980 840 760 750 590

Note: Any two means not marked with the same letter are significantly different at 1 °/o level.

also increased with irrigations up to seven, and the percentage of hollow seed decreased. The seven irrigations regime also resulted in the greatest yield per millimeter of water used by the plant. The level of moisture depletion before irrigation had no significant effect on any of the factors studied. The mean seed yield and consumptive use for safflower is reported in Table 12. Hoag et al. 41 reported that yields up to 2270 kg seed per hectare have been obtained in western North Dakota with careful water management and when diseases were not

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severe. To minimize the danger of crop loss by flooding and root rot, a recommended practice is to fall irrigate land that will be seeded to safflower. This procedure delays the need for supplementary water until shortly after flower buds start to form. This is the time when an adequate moisture supply is most important. When the land is fully irrigated and rainfall is near average, only one irrigation may be necessary. If two irrigations are needed, the second may best be applied during the flowering period in late July. In Arizona, Abel 32 reported that seed yield was significantly lower when irrigation was withheld until plants had used 90% of available water, than when soil water depletion was limited to 60 or 70%, but not when irrigation ended 5 days before 95% flowering instead of 8 to 16 days after that stage. Early cessation of irrigation hastened maturity by 5 to 15 days, decreased weed growth, and reduced the N requirement. The effect of applied N varied with sowing date, irrigation regime, and cultivation, with 336 and 84 kg N per hectare giving highest seed yields with the December and February sowings, respectively. Mexican Studies In the northwest and El Bajio regions of Mexico, Garcia and Quilantan40 reported that safflower is a suitable oil-seed crop especially for cultivation in winter under irrigation. The best varieties are Gila, N-6, and N-8055, which are sown in November to December. As a result of trials in 1962 to 1963, it was recommended that an irrigation should be given to encourage germination and 130 mm be applied at 30, 60, and 120 days from sowing — and 100 kg/ha of N should be applied at sowing. Detailed and thorough investigations have been carried out on the irrigation of safflower in five districts of Mexico (Secretana de Recursos Hidraulicos 50 ). The results are summarized in Table 13. The conclusions of these studies are that generally, safflower tolerates a fairly wide range of minimum moisture in the soil between irrigations, with only a moderate effect upon the yield. However, it is recommended that the soil moisture not be allowed to fall below 20% of the available range. In District 14 the salinity conditions were much more severe than in the other districts and consequently the drier treatments gave a significant drop in the yield. It is recommended, therefore, under conditions of higher soil salinity, to prevent the soil moisture from falling below 40% of the available range. Polish Studies In pot experiments in Poland, Seydlitz49 showed that drought (30% of the capillary potential) during emergence to the foliar-rosette stage did not adversely affect growth and yield of safflower. Water deficiency during rapid growth (from rosette formation to flowering) hindered growth and prolonged the vegetative period. Water deficiency during flowering and ripening markedly reduced yield of achenes, yield and percentage of oil, and also reduced the vegetative period. Indian Studies In India I.C.R.I.S.A.T. 42 reported there were no significant differences in seed yields of safflower or chickpeas sown between sorghum rows 1 or 2 weeks before or immediately after harvesting the sorghum. One irrigation to safflower and chickpeas sown in the winter season after harvesting sorghum gave significantly higher yields than no irrigation or when both crops were sown on soil fallowed during the monsoon season. In Maharashtra, India Mundel 48 reported that two safflower varieties given 0 to 150 kg N per hectare yielded 18.9 to 21.8 kg seed per hectare under rainfed conditions and 28.4 to 33.3 kg/ha with irrigation; Gila tended to give higher yields than N62-8 and the differences in yields obtained from applying N at different rates were nonsignificant. Suryanarayana51 studied the effects of three irrigation intervals of 40, 60, or 80 mm

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CRC Handbook of Irrigation Technology Table 13 SUMMARY OF IRRIGATION EXPERIMENTS WITH SAFFLOWER IN MEXICO District 14 Minimum % of available moisture Number of irrigations Depth of irrigation (cm) Yield of grain, t/ha

30 5 67 2.7

40 6 68 3.1

10 4 61 2.0

20 5 65 2.3

10 2 41 4.6

20 3 57 4.8

10 5 63 3.8

20 6 65 3.7

30 7 73 3.6

Pre°

10 3 56 2.3

20 3 52 2.5

30 4 63 2.7

Pre°

3 4 57 2.9

8 5 66 3.0

20 7 82 3.1

District 24 Minimum % of available moisture Number of irrigations Depth of irrigation (cm) Yield of grain, t/ha

0 2 51 4.4

District 38 Minimum % of available moisture Number of irrigations Depth of irrigation (cm) Yield of grain, t/ha

0 4 55 2.9

1 20 3.1

District 38 R Minimum % of available moisture Number of irrigations Depth of irrigation (cm) Yield of grain, t/ha

0 2 38 1.6

20 1.4

District 10 Minimum % of available moisture Number of irrigations Depth of irrigation (cm) Yield of grain, t/ha

0 4 53 2.8

" "Pre" indicates a single irrigation before planting. From Secretaria de Recursos Hidraulicos, Resultados de once experimentos realizados en los distritos de riego durante el subciclo de invierno 1974-1975, Mexico, 1926-1976. With permission.

cumulative evapotranspiration (CE) in Bangalore, India, and three irrigation depths of 100, 75, and 50% of water evaporated on growth and yield of safflower were determined. Application of 50 mm irrigation water after 60 mm CE gave the highest seed and oil yields, 2.08 t and 585 kg/ha, respectively, and the highest water use efficiency, 456 kg seed per millimeter. Yields were decreased with further delay in irrigation. The consumptive use of water decreased with a decrease in the irrigation water applied at each irrigation and at all intervals. The average consumptive use of water for high economic returns was about 450 mm and the optimum interval between irrigations was about 15 days. It was suggested that the can-evaporimeter may be used for scheduling irrigation of safflower, as the evaporation from the can-evaporimeter is closely related to the consumptive use of water. Mahapatra and Singh47 reported that safflower gave the highest seed yields with four irrigations at Delhi and in Rajasthan, with three irrigations in Madhya Pradesh, and with two irrigations under the wet and mild climatic conditions of the Tarai region in Uttar Pradesh.

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In Rajasthan, Bajbai et al.34 studied the response of safflower variety Nagpur 7 to irrigation at 30, 50, or 70% available soil moisture in the 0- to 60-cm soil layer using 0 to 60 kg P2O5 and 0, 60, 80, or 100 kg N/ha. The soil was a coarse loam in semiarid conditions. The highest seed yield, 1.5 to 1.6 ton/ha, was achieved when irrigation was started at 30% available moisture with 80 kg or 60 kg N + 60 kg P 2 O 5 per hectare. This gave a consumptive use efficiency of 38 kg seed per 1 cm water. Irrigation at higher soil moisture regimes induced vegetative growth and reduced yields. Summary and Conclusions Safflower, in general, benefits from an adequate supply of moisture which should be supplied by irrigation if the seasonal rainfall is insufficient or poorly distributed. The period in which moisture is most important is during the budding, flowering, and seed development stages. The levels of critical moisture lie somewhere in the range of 20 to 30% of the available moisture. Irrigation should generally cease several weeks before harvesting. Good correlations have been found in studies in various countries between irrigation and the uptake of nutrient elements. Fertilizers applied with irrigation have been more effective in raising crop yields than fertilizers under conditions of moisture stress. SUNFLOWER Introduction The sunflower plant (Helianthus annuus) is a native of North America and was introduced into Spain from Central America before the middle of the 16th century. Its culture by the American Indians was at an advanced stage when the first Europeans observed it. Sunflowers are now distributed in all parts of the world, but the major producing countries are the U.S.S.R., Romania, Yugoslavia, Argentina, Bulgaria, and the U.S. Sunflower production has become of economic importance due to the potential of high-oil yielding varieties and due to the increasing demand for edible vegetable fats and oils. Sunflower oil is a quality edible oil, being high in polyunsaturated fatty acids. It is used in cooking, salad dressing, margarine, soap, and as a drying oil in paint. The high-protein sunflower meal remaining after extraction of the oil from the seed is used successfully as an ingredient in mixed animal feeds. Sunflower hulls can also be used as a roughage ingredient in livestock feeds. Total annual world production is about 10 million tons of seed from 9.5 million ha. The growing period varies from 70 days in the northern European countries to 200 days in the high elevations of Mexico. In the subtropical regions, under irrigation, the average growing season is about 130 days. Most of the sunflower is grown under rainfed conditions, but there is an increasing use of irrigation in regions where the water supply through precipitation is not reliable. The root system is very strong and deep and may penetrate beyond 2 m. Irrigation trials on sunflowers have been carried out in many countries and some of the results will be summarized below. The U.S. Leaves of a dwarfed form of sunflower were treated with P32 — labeled NaH2PO4 by Wilson and McKell100 at various levels of soil moisture stress. After 24 hr, plants at 0.3 atm had absorbed 80% of the applied phosphorus as compared with an absorption of 33% at 5 atm and 15% at 16 atm. Moisture stress also resulted in less effective translocation of the absorbed phosphorus. In plants at 0.3 atm, 16% of the absorbed phosphorus was translocated from the leaf in 24 hr as compared with less than 7% in plants at 5 and 16 atm. After an initial lag the amount of phosphorus translocated

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CRC Handbook of Irrigation Technology Table 14 EFFECT OF SOIL MOISTURE STRESS ON PHOSPHORUS ABSORPTION AND TRANSLOCATION Tension (atm)

Phosphorus absorbed (%)

Absorbed phosphorus translocation (%)

Total phosphorus translocated (mg)

0.3 + 0.0 5 ±2 16 ± 1

8.0 3.3 1.5

16 6.9 6.4

0.95 0.18 0.08

Table 15 EFFECT OF MOISTURE STRESS ON DISTRIBUTION OF TRANSLOCATED PHOSPHORUS Translocated phosphorus in plant parts (%) Tension (atm) 0.3 ±0.0 5 ±2 16 ±1

Growing tip

Stem

Root

55 37 28

20 39 43

24 22 26

from the treated leaf was approximately linear in time. Moisture stress altered the relative distribution of the translocated phosphorus within the plant. Plants with adequate moisture accumulated a higher concentration of phosphorus in growing regions than did plants exposed to moisture stress. The effectiveness of phosphorus applications to leaves was reduced as availability of water to the plant was decreased by soil moisture stress. Some of the data is presented in Tables 14 and 15. Lehman et al.,69 in California, conducted a trial on furrow and sprinkler irrigation of sunflowers planted on March 15. Irrigation treatments were designed to range from wet to dry and were based on pan evaporations of 1.5, 2.5, 3.5, and 4.5 in. of water. Plants were uniformly irrigated until they were about 3 in. tall. No significant differences were obtained among treatments for production. However, the driest treatment in both tests yielded less than all other treatments. Yields averaged 2821 kg/ha for the sprinkler and 1879 kg/ha for the flooded treatments. These two experiments were about a half a mile apart and it is probable that both the irrigation method and the test location contributed to the difference of yields. From these experiments, it appears sunflowers can tolerate fairly large differences in water application rates once the plants have become established. There is, however, a significantly higher average yield with sprinkling as compared to flood irrigation. Romania Albinet et al.53 reported on irrigation of sunflowers in the Prut valley. The highest seed and oil yields were obtained by irrigation when soil moisture level was at half the soil capacity, or by three irrigations, respectively, after head formation, flowering, and seed formation. Application of 128 to 160 kg N, 96 to 128 kg P, and 160 to 200 kg K per hectare with irrigation, markedly increased seed oil content. Optimum plant population was 50,000 to 60,000 plants per hectare with irrigation and 40,000 to 50,000 plants per hectare without irrigation.

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Sipos and Paltineanu89 compared water consumption of sunflower to maize, sugar beet, potato, soybean, and other crops. In southern Romania, 55 to 80% of the water requirements of sunflower were provided by water stored in the soil at sowing and rainfall during growth, leaving deficits of 20 to 45% to be made up by irrigation. In trials at Fundulea and Brailia, irrigation to maintain soil water content at 50% to a depth of 80 cm of soil increased sunflower seed yields to 2.73 to 3.03 t/ha as compared to 2.13 to 2.60 t/ha without irrigation. Irrigation plus an application of 80 kg N + 80 kg P2O5 per hectare gave further increases to 3.62 to 3.66 t/ha. Paltineanu and Sipos82 reported that values of evapotranspiration of sunflower during the 1969 to 1973 growing seasons were approximately 512 mm. Evapotranspiration was highest during the head formation and seed setting physiological maturity stages and was closely correlated with plant height, air temperatures, wind speed, and relative humidity. Potential evapotranspiration values calculated by means of the Penman formula were closely correlated with soil water depletion and could be used for computer scheduling of irrigation requirements, but those obtained with the Thornthwaite formula showed a good correlation only up to 10 July. Pirjol et al.83 reported pot trials with sunflower cv. Record grown in soil maintained at 70% of field capacity (control) or subjected to drought stress (40% of field capacity) for 10-day periods during (1) vegetative growth, (2) heading,(3) flowering, or (4) seed formation, after which the soil was restored to 70% of field capacity. The results for different varieties are shown in Table 16. From these results it can be seen that moisture stress at any time reduces the yield of seeds and the percentage of oiL It is especially harmful in the periods of flowering and seed formation. Pirjol 81 grew eight lines of sunflower at either (1) optimum soil moisture content throughout (70% of field capacity) or (2) subject to drought (40% of field capacity) for 10 days during flowering. Plant height, root length, leaf area, diameter of head, DM (dry matter) accumulation, seed yields, and oil content were all significantly decreased by treatment (2). Bulgaria Vitkov and Gruev 96 studied sunflowers given 90 + 90 + 90 or 180 + 180 + 180 kg/ha of N + P2O5 + K 2 O, respectively. Irrigation was given whenever soil-moisture contents during or periods between emergence and heading, heading and late flowering, and late flowering and maturation fell to (1) 60, 70, and 60 or (2) 70, 80, and 70% of field capacity, respectively. The highest seed and oil yields were obtained on plots given the higher rate of fertilizers and irrigated at (2). Yields were not appreciably increased either by fertilizers or by irrigation alone. Irrigation significantly increased seed oil contents. Vitkov et al. 97 made field trials with sunflowers grown in soil with moisture contents maintained at 60 to 70% of F.C, (60% up to bead formation, 70% up to initiation of wilting of beads, and 60% up to harvesting) or at 70, 80, and 70% and given 90 or 180 kg each of N, P2O5, and K 2 O gave the highest average yields of 3.99 t seeds and 1.82 t oil per hectare on plots with soil-moisture contents of 70, 80, and 70% and given 180 kg/ha each of N, PiO5, and K 2 O. Irrigation increased seed oil contents of 46.20 to 46.55% from 45.95 without it. The evapotranspiration by sunflowers during growth period was 438 mm and the daily mean evaporation was 3.0 mm. Mikhov, 73 in a field trial with irrigation, maintained the soil moisture content at 70, 80, and 70% of field capacity at early bud formation, at flower head development, and at full flowering, respectively. The optimum treatment for high yields of seed and oil was achieved by two to three irrigations during flower head development, full flowering, and seed development us-

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CRC Handbook of Irrigation Technology Table 16 EFFECT OF MOISTURE STRESS ON SUNFLOWER YIELD AND OIL CONTENT IN POT TRIALS IN ROMANIA Variety

Moisture treatment No moisture stress (70