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THIS IS TO CERTEFY THAT THE THESIS PREPARED UNDER MY SUPERVISION
Roy Dennis Rouse
%ie Nature of Potassium Availability of Several
Indiana Soils and Methods of Evaluating It.
COMPLIES WITH THE UNIVERSITY REGULATIONS ON GRADUATION THESES
AND IS APPROVED BY ME AS FULFILLING THIS PART OF THE REQUIREMENTS
FOR THE DEGREE OF
LOFESSOR IN CHARQE OF TTHESIS
S o h o o i.
D e p a r t m e jjt
TO THE LIBRARIAN:-----
m THIS THESIS IS NOT TO BE REGARDED AS CONFIDENTIAL.
PHOFEBBOS USr OBAKOEi
GBAD. S C n o O I, FOKAI 9—3 - 4 9 —I M
THE NATURE OP POTASSIUM AVAILABILITY OF SEVERAL INDIANA SOILS AND METHODS OF EVALUATING IT A Th.esis Submitted to tbe Faculty of Purdue University by Roy Dennis Rouse In Partial Pulfillment of tbe Requirements for the Degree of Doctor of Philosophy August, 1949
ProQuest Number: 27712229
All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is d e p e n d e n t upon the quality of the copy subm itted. In the unlikely e v e n t that the a u thor did not send a c o m p le te m anuscript and there are missing pages, these will be noted. Also, if m aterial had to be rem oved, a n o te will ind ica te the deletion.
uest ProQuest 27712229 Published by ProQuest LLO (2019). C opyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States C o d e M icroform Edition © ProQuest LLO. ProQuest LLO. 789 East Eisenhower Parkway P.Q. Box 1346 Ann Arbor, Ml 4 8 1 0 6 - 1346
ACKNOl¥LEDGMENTS To h.is major professor. Dr. B. R. Bertrams on, the author wishes to express his sincere appreciation for the invaluable assistance and constant encouragement throughout the course of this investigation. The author is also grateful to Dr. J. L. White for his assistance and suggestions in the minerological studies, and to Dr. H. J. Yearian of the Physics Department for the liberal use of the x-ray equipment. The writer wishes to thank the members of his advisory committee, the other members of the staff, the graduate students of the Agronomy Department, and his neighbors, for timely consideration and help. Grateful acknowledgment is also extended to Dr. G. H. Hoffer for his helpful comments and to the American Potash Institute whose financial aid made this work possible. To his wife, whose help and encouragement has done much to make the completion of this work possible, he is deeply grateful.
TABLE OP CONTENTS INTRODUCTION.........
EXPERIMENTAL PROCEDURE................................... 16 Samples Used in the Investigation of Chemical Methods .......... .... . ... 18 Potassium Analysis
Chemical Methods for Determining the Supplying Power of Soils
Comparison of the Potassium Extracted by IN Neutral Ammonium Acetate, 0.2N Nitric Acid, and 0 .IN Monochloroacetic Acid Buffer Solution with and without Previous Treat ment of the Sample with Six Per Cent 20 Hydrogen Peroxide...... Complete Removal of Organic Matter Followed by Repeated Extractions. . . . . . . . . . . .
Extractions with IN Nitric Acid...........
Extractions with IN Boiling Nitric Acid...... 22 Seasonal Effect and Effect of Oven Dryings on the Exchangeable Potassium and Potassium Supply ing Power of Soils under Field Conditions.... 22 Effect of Previous Fertilizer Treatments on Exchangeable Potassium and Potassium Supply ing Power of Soils....................
Influence of the Degree of Calcium Saturation on the Increase in Exchangeable Potassium of Brookston Silty Clay Loam onDrying .....
Effect of the Removal of Free Iron Oxides in Soil on Release of ExchangeablePotassium.... 24 Fractionation of Samples
Preparation of Soil Fractions, for Chemical and ...... X-ray Analyses
Preparation of Mineral Fractions for Chemical Analysis ......
TABLE OF CONTENTS (continued) Potassium Supplying Power of SoilFractions
Potassium Supplying Power of Mineral Fractions.... 27 X-ray Analyses........
RESULTS AND DISCUSSION....................... .......... 29 A Chemical Method for Determining the Supplying Power of Soils
Seasonal Effect upon Exchangeable Potassium and Potassium Supplying Power under Field Con ditions
Effect of Oven Drying at 70^ G before Removal of Exchangeable Potassium..............
Effect of Previous Fertilizer Treatment on Exchangeable Potassium and Potassium Supply ing Power of Soils.......
Influence of the Degree of Calcium Saturation on the Increase in Exchangeable Potassium from Drying of Brookston Silty Clay Loam.......... 54 Effect of the Removal of Free Iron Oxides in Soils on Release of Exchangeable Potassium... 56 Chemical Analyses
of Soil Fractions
of Mineral Fractions .......... 66
X-ray Analyses of
X-ray Analyses of Fine Sand Fraction (0.05: to 0.02 m m).......................
X-ray Analyses of Silt Fraction (0.02 to 0.005 mm). 74 X-ray Analyses of Fine Silt Fraction (0.005 to 0.002 mm)..........
X-ray Analyses of Clay Fractions Using a One Per Gent Suspension in Preparing the Slides...... 78 X-ray Analyses of the Coarse Clay Fraction (0.005 to 0.001 mm and 0*002 to 0.001 mm).7B X-ray Analyses of the Medium Clay Fraction (0.001 to 0.0002 m m ) ............. 82
TABLE OP CONTENTS (continued) Page X-ray Analyses of the Pine Clay Fraction... (less-than-0.0002 mm)............
X-ray Analysis of Clay Fractions Using a Two Per Cent Suspension in Preparing the Slide.. 91 X-ray Diffraction Patterns of Mounts Pre pared from Two Per Cent Suspensions Compared to Those Prepared from On© Per Cent Suspensions ...........
X-ray Analyses of Undried Samples............ 95 S m m A R Y AND CONCLUSIONS.......
III IV V
Notes on the Technique Used in Making Potassium Analyses with the Perkins-Elmer Flame Photometer, Model No. 52-A
Methods Used in Comparing the Potassium Extracted by IN Neutral Ammonium Acetate, 0.2N Nitric Acid, and 0 .IN Monochlorocetic AciU Buffer Solution with and without Previous Treatment with Six Per Cent Hydro gen Peroxide 108 Methods used in the IN Boiling Nitric Acid Study ......................... ......... 110 Method For Removal of Free Iron Oxide,. Methods Used in X-ray Analysis.......
112 113 115
LIST OP FIGURES AND TABLES List of Figures Figure
The nonexchangeable potassium removed by plants compared to that removed by IN nitric acid..................
The nonexchange able potassium removed by plants compared to that extracted by IN nitric acid after a previous extraction .................. with IN nitric acid
The nonexchangeable potassium removed by plants compared to that extracted by boiling thirty minutes with IN nitric acid after two previous extractions with IN nitric acid at room temperature........ * 37
The nonexchangeable potassium removed by plants compared to the exchangeable re moved by IN neutral ammonium acetate....... 38
The nonexchange able potassium removed by plants compared to the exchangeable removed by 0.2N nitric acid...........
The effect of boiling time on the extraction of potassium at givensoil-acid ratios
The effect of soil-acid ratio on the extraction of potassium at given boiling times........ 43
The nonexchange able potassium removed by plants compared to that removed by IN boiling nitric acid............. .... ..............
The potassium supplying power of three differ ent soil fractions ..... .... ... 62
The potassium supplying power of five fractions of 16 soils .............. 63
The potassium supplying power of 16 soils by size fractions ...........
X-ray diffraction patterns of four potassium bearing mineralsand quartz.............
List of Figures (continued) Figure 13.
Page X-ray diffraction patterns of fine sand fraction (0.05 to 0.02 mm) arranged in decreasing order of supplying power of fractions ...................
X-ray diffraction patterns of silt fraction (0.02 to 0.005 mm) arranged indecreasing order of supplying power of fractions
X-ray .diffraction ^patterns of fine silt fraction (0.0Ô5 to 0.002 mm) arranged in decreasing order of supplying power of fractions ...........
X-ray diffraction patterns of coarse clay fraction (0.005 to 0.001 mm), prepared from one per cent suspensions, arranged in decreasing order of supplying power .......... of fractions
X-ray diffraction patterns of coarse clay fraction (0.002 to 0.001 mm), prepared from one per cent suspensions, arranged in decreasing order of supplying power of fractions .....
X-ray diffraction of medium clay fraction (0.001 to 0,0002 mm), prepared from one per cent suspensions, arranged in decreas ing order of supplying power of fractions...83
The relative intensity of reflection from the 0 0 1 crystal plane at 9.9 A spacing for the 0.001 to 0.0002 mm fractions (mounts prepared from one per cent sus pensions
X-ray diffraction patterns of fine clay fraction (less-than-0.0002 mm), prepared from one per cent suspensions, arranged in decreasing order of supplying power of fractions...........................
The relative intensity of reflections from the 0 0 1 crystal plane at 9.9 A spacing for the less-than-0.0002 mm fraction (mounts prepared from one per cent suspensions)......
List of Figures (continued) Figure
X-ray diffraction pattern of fine clay fraction (less-than-0.0002 mm) pre pared from two per cent suspension, arranged in order of decreasing supply ing power ....................
X-ray diffraction patterns of undried coarse clay (0.002 to 0.001 mm) arranged in .decreasing order of supplying power
X-ray diffraction patterns of undried medium clay (0.001 to 0,0002 mm) arranged in decreasing order of supplying power..... 98
X-ray diffraction patterns of undried fine clay (less-than-0.0002 mm) arranged in decreasing order of supplying power..... 90
X-ray diffraction patterns of undried fine clay superimposed to show relation between height at illite spacing and potassium supplying power of the fraction..100
List of Tables Table
Tabulated information on Indiana soils whose potassium supplying powers were studied.... 17
Chemical properties of the soils used in the study of potassium supplying power........ 19
A comparison of the amount of potassium extract ed by IN ammonium acetate, 0.2N nitric acid, and 0 .IN monochloroacetic acid buffer solution with and without a previous treatment with six per cent hydrogen peroxide....... ....... ......... .. 31
Potassium extracted by successive extractions after complete removal of organic matter with hydrogen peroxide ..................
The change in the potassium status of several soils from fall to spring............ .
The effect of oven drying at 70*^ C on the exchangeable potassium..................... 50
Effect of previous fertilizer treatment on the present exchangeable potassium and potassium supplying power.. . . . . . . . . . . . .
Effect of added increments of calcium hydroxide on the increase in exchangeable potassium from drying Brooks ton silty clay loam..... 55
Effect of removal of free iron oxide on the exchangeable potassium of soils........... 58
10. 11. 12. 13.
Weight of fractions from mechanical separation of 100 grams of soil.......................
Weight of fractions from mechanical separation of 100 grams of soil .............
The potassium supplying power of four potassium bearing minerals .... . . . . .
The relative intensity of reflections from 0 0 1 crystal plane at 9.9 A spacing for the less-than-0.2 micron fraction...... .......94
THE NATURE OF POTASSIUM AVAILABILITY OF SEVERAL INDIANA SOILS AND m T H O D S OF EVALUATING IT
INTRODUCTION Progress in science has followed the development of new methods and techniques.
The introduction of flame photo
meter for the quantitative determination of potassium has made possible rapid and accurate evaluation of the potassium found in soil extracts.
But the question still remained, "What
extract will remove from the soil an amount of potassium which is representative of that soil *s potassium productivity status?" It was the general purpose of this research to obtain a satisfactory answer to this question. Since Liebig disposed of the humus theory, there has been a continuous search for some chemical test which can be used to predict a:ccurately the fertilizer needs of soil for crop production.
At present, the most widely accepted
methods for appraising the potassium availability, are those which measure the combined watersoluble and exchangeable potassium.
Tliis is usually referred to as the available
potassium. Many Investigators have postulated that the water sol uble potassium is in equilibrium with the exchangeable and exchangeable, in turn, is in equilibrium with the nonexohangeable potassium.
If this is true, and the equilibrium is
sufficiently rapid, then a measure of the exchangeable potassium should be a sound criterion for formulating potassium fertilizer
However, it is realized that this is not an
instantaneous equilibrium reaction; since if it were, there would be little need for potassium fertilization on most soils due to the large reserve of nonexchangeable potassium. The results from numerous field and greenhouse experi ments show that the level of exchangeable potassium is de creased more rapidly in some soils than others by cropping, and that with a given level of exchangeable potassium, some soils will show greater crop response to additions of potassium fertilizer than other soils.
This indicates that
soils differ in the rate of release of nonexchangeable potassium.
The rate of release or the amount of potassium
which becomes available to crops from the nonexchangeable form has been termed the "potassium supplying power" of a soil. In 1935, Hoagiand and Martin (24) pointed out the need for some method of determining this potassium supply ing power of the soils, but they were unable to find a correlation between the amount of potassium removed by continuous examined.
cropping and any of the chemical techniques Considering the many problems involved, they
could see no reason to expect that such a method could ever be developed which would hold for widely diverse soils, crops and climatic conditions. About 1938, Bray and DeTurk (8) stressed the importance of the potassium supplying power of soils.
Wood and DeTurk (46)
observed that the potassium removed by boiling 10 grams of soil with 100 ml of one normal nitric acid for
ten minutes appeared to be a measure of the potassium supplying power of soils. The variation in the supplying power of soils has been noted by several investigators, (5, 10, 21, 25, 39, 41) and it is generally agreed that the best method of compari son is that of continuous cropping and determining the amount of potassium removed by several harvests minus the decrease in exchangeable potassium.
Most of these
investigators have found little correlationvith the amount of exchangeable or total potassium in the soil. Even with this apparent evidence showing quacy of exchangeable potassium for purposes
the inade of fertilizer
recommendations it is still the standard basis for making potassium fertilizer recommendations.
However, even its
strongest proponents contend that the crop must be allowed to indicate the significance of the amount measured in terms of growth response to added potassium.
requires the results of numbrous, carefully planned field experiments.
Some workers recommend the practice of in
creasing the exchangeable potassium in all soils to a minimum value (about 200 lbs. per acre for midwest soils). These indicate that exchangeable potassium does not give sufficient information and that some better technique is needed for predicting potassium fertilizer practices. The continuous cropping method is not suitable for pur poses of fertilizer recommendations, therefore some rapid chemical method is desirable.
If a method for measuring the potassium supplying power of soils were available, it should be possible to make efficient use of the reserve potash in soils without sacrificing crop yields.
At the same time, it would be
possible to make more efficient use of potassium fertilizer by avoiding luxury consumption. The objectives of this investigation were to develop a chemical method which would correlate well with the potassium supplying power of 23 Indiana soils as determined by heavy continuous cropping with ladino clover.
such a method was developed, the nature of this potassium availability was to be investigated in order to gain funda mental knowledge as to the mechanism of the potassium equi librium in soils.
LITERATURE REVIEW Pag© and Williams (35) credit Hiss ink with, the idea that an equilibrium exists between the different forms of potassium in soils.
Since that time, numerous studies per
taining to the availability of the different forms of potassium in soils have been made. In a series of papers from 1912-1931, Praps (15, 16, 17, 18, 19, 20, & 21) presented considerable evidence showing that the best measure of the availability of potassium to plants was the amount of potassium removed by plant growth.
He conducted numerous pot experiments with
Texas soils to determine the amount of potassium removed by cropping and measured the different forms of potassium in the soil before and after cropping.
showed that the decrease in exchangeable potassium (extracted with ammonium chloride) or active potassium (extracted with 0.2N nitric acid) failed to account for the amount of potassium absorbed by crops. Prom his studies, he considered that the active potassium was the best measure of the potassium available to plants.
However, there was a correlation between the
amount of potassium removed by plants and the waters oluble, exchangeable, acid soluble, acid insoluble, and total potassium. soluble.
The lowest correlation was with the acid in
Martin (33), in 1929, reported that the decrease in exchangeable potassium of thirteen California soils, which had been subjected to continuous cropping and to fallow for twelve years, in no case accounted for the potassium removed by the plants.
He concluded that the plants had obtained
a part of their potassium from a nonexchangeable form or that the exchangeable had been replenished by the nonexchangeable. One of the earlier studies stressing the value of non exchangeable potassium was made by Getroiz (22).
placed the exchangeable potassium from soil, saturated the complex with calcium, and then added potassium in varying amounts.
With the crops and soils studied, hé found that
sufficient potassium was released from some nonexchange able form to permit as good growth as was obtained on the original soil. Hoagiand and Martin (23) subjected several soils, with and without added potassium, to continuous cropping with barley and tomatoes for a period of five years.
results of this investigation showed that only when the exchangeable potassium is very high, can all of the potassium removed by crops be accounted for by decreases in exchange able potassium.
In such cases the percentage composition
of the plants indicate "luxury" consumption.
In all cases,
the exchangeable potassium decreased on cropping until finally a point was attained at which the amounts recovered by the ammonium acetate method were substantially constant.
This level varied with different soils and showed no re lation to the amount of potassium released from nonexchange able sources, after the minimum level had been reached.
some soils, the minimum level may be adequate for normal crop growth, but in other soils, the solubility of the non exchangeable form is too low and plants suffer from a de ficiency of potassium. Ho agi and and Martin (24) emphasized the need for some methods of determining the potassium supplying power of soils.
From their investigations, they concluded it was
unlikely that such a method would ever be developed in which it would be possible to predict for widely diverse soils, crops, and climatic conditions, the response of crops to potassium fertilization under field conditions with any degree of success. Abel and Magistad (1) investigated the release of nonexchange able potassium on several Hawaiian soils by continuous cropping with soybeans and sorghum.
that approximately 100 pounds HgO per acre foot was made available from nonexchangeable sources annually on limed soils and about 75 pounds on unlimed soils.
They found that
soils having very low replaceable potassium at the be ginning were able to release potassium from nonexchangeable sources as readily as soils rich in replaceable potassium. This indicated that the rate of release of potassium cannot be predicted from knowledge of the replaceable potassium.
Bray and DeTurk (8) suggested that the level of re placeable potassium is of value as a fertility measure only in so far as it represents the soils ability to main tain that level.
They pointed out that the potassium
supplying power is the important factor in the future potassium fertility of a soil.
Their studies on potassium
fixation and liberation supported the contention that an equilibrium exists between the different forms of potassium in the soil.
In offering an explanation for this equilibrium
mechanism, they suggested that the partly weathered sur faces of primary silicate minerals might be expected to offer an excellant chance for slow movement of potassium ions both into and out of the lattice layers made less compact
by oxidation and hydration, but still compact
enough to prevent the usual speed of replacement shown by the montmorillonite type.
They also suggested the possibility
of the substitution by potamsium within the lattice of base-exchange clay minerals but considered this less likely than the former. Praps and Pudge (21) found a high correlation between the quantity of potassium taken up by plants and the quantity of acid soluble and active potassium.
soluble fraction was determined by digesting 10 grams of soil at room temperature for 24 hours with 100 ml of 12 per cent hydrochloric acid.
The active potassium was the
fraction extracted by 0.2N nitric acid.
Wood and DeTurk (46) presented evidence in favor of an equilibrium between the nonexchangeable and the re placeable.
This nonexchangeable was the fraction extract
ed by boiling ten grams of soil in 100 ml of IN HNO^ for ten minutes.
The acid soluble is believed to be more im
portant from the standpoint of crop production in the near future than the available.
They concluded that the "stay
ing power" of a soil under continuous cropping is closely correlated with its content of acid soluble potassium. They observed that previous potassium fertilizer treatment in the field for many years had little effect on the amount of potassium fixed in the various t orras^ Pine, Bailey, and Trmog (14) contributed additional evidence toward the existance of an equilibrium when they found that freezing—thawing treatments resulted in potassium release in some soils, while in others no change or even fixation occurred.
They associated these last two
results with the illite nature of the soils.
Purvis (6) found that the amount of potassium in fixed and available forms was in a state of change even when the soils were kept under apparently constant conditions of moisture temperature. DeTurk, Wood, and Bray (11) again pointed out the existance of an equilibrium between the fixed and re placeable potassium when they were able to make the reaction proceed in either direction by altering the concentration relations.
They considered that the potassium fixed from
added fertilizer increased the reservoir of that in the
10 soil which renews the replaceable potassium following its removal by crops. Bear, Prince, and Malcolm (6) grew alfalfa in two gallon pots on twenty New Jersey soils for a period of one year, and harvested seven crops.
The amount of
potassium released from nonexchangeable forms varied con siderably, and several soils fixed considerable quantities. They concluded that some soils were in greater need of potassium than would have been anticipated from a knowledge of either their total or their exchangeable supplies of the element. Chandler, Peech, and Chang (10) grew ladino clover on eleven New York soils.
The amount of nonexchangeable
potassium released during the harvest of six crops of clover varied from 39 to 358 pounds per acre.
that the exchangeable potassium content of a soil is not sufficient to make fertilizer predictions, and concluded that it is necessary to know the critical level for that par ticular soil and crop, and the rate at which the exchangeable potassium is replenished from the nonexchangeable form. By determining the exchangeable potassium content of soils at different times of the year, these authors found that the exchangeable potassium content of many soils de creased appreciably during the cropping season.
in the exchangeable potassium content of 28 soils on which alfalfa was growing vigorously ranged from plus 18 to minus 82, with an average decrease of 18 pounds.
From this study
They suggested that the potassium supplying power may be estimated by determining the exchangeable potassium in early spring and again in the fall* Winters (45) emphasized the need for caution in using soil test results as a basis for fertilizer recommendations when knowledge of the soil, climate, or crop conditions are inadequate.
Unless sufficient data were available for a
growth-response curve, he considered it doubtful whether fertilizer recommendations based on soil tests would be more satisfactory than general recommendations for a large portion of the state.
This had been Bray's contention since
he published his article on the new concept in the chemistry of soil fertility (37)* Attoe and Truog ( 3) proposed that the potassium of soils be divided into three categories with regards to its availability to plants.
These included the readily avail
able, or water soluble and exchangeable forms of potassium; the moderately available, or fixed and biotite forms (20 grams soil extracted with 400 ml 0.5N HGl for one hour); and the difficultly available or feldspar and muscovite forms.
They demonstrated the availability of the fixed
or moderately available potassium in soil by growing oats and corn in pot culture.
Wliere the readily available
potassium had been extracted with a salt solution the yields were 62 percent of those on the unextracted soil which contained 164 pounds per acre of exchangeable
potassium, but where the moderately available potassium had been extracted with 0.5N HGl, the yields were only 20 per cent as much as on the unextracted soil.
They state that
the mechanism in soils which makes possible the retention of potassium in exchangeable and fixed forms, and their conversion from one to the other, is a most important feature of soils. In 1946, Ayers and Takahaaki (4) reporting on the results of four and one-half years continuous cropping with napier grass (19 crops) without potassium additions show ed that on the Hawaiian soil studied, nonexchangeable potassium was released in amounts ranging from 3,400 to 4,200 pounds K^o per acre for the four and one-half year period.
The level of potassium in the plants decreased
during the first two and one-half years of cropping after which there was little change.
Potassium additions failed
to give a response on this soil even after many crops had been produced.
The amount of potassium removed was greater
following the addition, but the amount derived from the nonexchangeable was less since the increase in amount removed was not sufficient to account for the amount added. Martin, Overstreet, and Hoagiand (35) made several observations concerning fixation and release of potassiuqjL. They found that when potassium was fixed, other cations were released but hydrogen was not.
The fixation reaction
was not instantaneous but increased from ten minutes to 48 hours.
Fixation was less at lower pH values.
of potassium fixed was not related to the exchange capacity. The power of soils for fixation was almost lost by digest ing the soil with hydrogen peroxide (this treatment decreased the exchange capacity but little).
It was thought that
this could probably be accounted for by the acidity developed rather than caused by the destruction of organic colloids. The release of potassium from the nonexchangeable to the replaceable form by grinding cannot be measured with certainty because of the presence in the soil of potassium bearing minerals.
It was found (35) that soils fixed
rubidium to a degree comparable to that of potassium. Therefore, grinding experiments were conducted with rubidium, an ion not normally present in the soil.
One soil with
an exchange capacity of 26 m.e. per 100 grams that had fixed 1.01 m.e. rubidium per 100 grams of soil, on grinding for 72 hours in a ball mill released 27 per cent of that fixed. A soil which had an exchange capacity of 6.5 m.e. per 100 grams fixed 1.05 m.e. rubidium per 100 grams of soil, on similiar grinding released 50 per cent of that fixed, Stewart and Volk (41) in a study using the continuous cropping technique found that 39 to 87 per cent of the potassium removed from the soil by the crops came from forms that were nonexchangeable at the start of the test.
Tliey attributed this to an equilibrium that exists in the soil between the exchangeable and nonexchangeable Terms of potassium.
They found that the amount of nonexchangeable
potassium bore no relation to the total potassium ex tracted by the crops, the potassium in the soil, or the decrease in exchangeable potassium that resulted from cropping methods. Reitemeier, Holmes, Brown, Klipp, and Parks (39) grew fifteen crops of ladino clover on 700 or 800 grams of soil. Fourteen soil samples were used; nine of these samples represented one soil series from Maine which had received a series of field treatments involving different potash and organic matter applications, the other five samples came from five additional eastern states.
released in two years on nine samples of soil from the fertility series varied from 90 to 562 pounds per acre. The other five samples ranged from 80 to 740 pounds per acre. The release of potassium from these soils by electrodialysis for thirty days, by the Neubauer procedure, and ten minutes boiling with IN nitric acid gave significant correlations with the amount removed by the clover.
regression relationship of clover and dialysis was oest from the viewpoint of precision and order of magnitude. Hydrocliloric and sulfuric acid were also investigated, but were inferior to nitric acid.^
Evans and Attoe (13) presented additional evidence to the varied supplying power of soils.
They grew ladino clover
and oats on six Wisconsin soils both virgin and cropped. Ladino clover removed more nonexchangeable potassium from the four soils which were relatively high in exchangeable potassium than did oats, but on the two soils with low exchangeable potassium the oats removed the most, probably because of their ability to grow well at low levels of available potassium.
In every case, liming of acid soils
repressed the removal of both exchangeable and non exchangeable potassium by oats.
¥/hen soils were leached
with GaClg-MgClg solution to reduce the content of exchangeable potassium prior to cropping, increases up to three times as much nonexchangeable potassium were absorbed from them by four crops of oats as from the unleached soils. They concluded from this that in determining the capacities of soils to supply crops with nonexchangeable potassium, the content of the exchangeable potassium should be similiar in all soils at the beginning of the cropping period. They concluded that high fixing power for potassium was closely associated with high supplying power of nonexchangeable potassium to crops and high pH and/ or high baseexchange capacity.
16 EXPERIMENTAL PROCEDURE The soils used in this study are described in Table 1. All information concerning the collection of the 23 samples, the greenhouse technique, and analyses made in obtaining a measure of potassium supplying power of these Indiana soils by plants may be found in H. L. Breland*s thesis (9).
brief, the samples were collected at three locations for each soil type.
Each sample was obtained by taking many
borings with a soil sampling tube over an area of about one acre.
The three composite samples were thoroughly mixed to
gether, and screened through a four-mesh sieve.
used in the greenhouse experiment was fertilized with adequate amounts of phosphorus and nitrogen.
bring the pH up to about 6.5*
stored moist in 50 pound lard cans with an open
flask of water in each to maintain the moisture content. For the greenhouse experiment ladino clover was grown continuously on 200 to 250 grams of soil for 493 days. Sight harvests were obtained. soil is
The difference In weight of
accounted forby the fact that a given volume of
soil wasadded to each can rather
than constant weight.
exchangeable potassium was determined on the soil both before and after growing the clover.
The material harvested
was analyzed for potassium and the total amount removed minus the decrease in exchangeable potassium gave the amount of potassium released from nonexchange able forms. All calculations pertaining to these data were recal-
Tabulated information on Indiana soils whose potassium supplying powers were studied. Major Profile Surface Physiography Parent Material Age and Drainage Soil Type Soil Color Group Phase -
Sampling Location Soil Region County
Soil Area of State Acres Per Cent . of Total
E F A A G E I C
5.44 4.50 1.30 0.78 3.38 7.07 2.70 1.34
1,254,300 1,036,800 300,200 180,500 781.400 1,631,400 656,200 307,800
Rush Randolph Starke La Porte Putnam Tippecanoe Clay I Newton, II & III Benton Jennings
Bottom Land Upland Terrace Upland
Light Light Light Light
Lawrence Martin Wayne Lawrence
H(L) L H(E) M
0.64 1.30 0.24 0.80
147,200 300,200 55,700 184,300
IV V IV II IV
Residual-Shale & Limestone Till-mixed Outwa sh-mixe d Alluvium Till-mixed Till-mixed
P Knox I Tipton, II White E III Carroll Dearborn K
Upland Terrace Bottom Land Upland Upland
Dark Light Medium Light Light
C A H I G
0.85 2.00 4.26 1.18 3.65
195,800 461,500 983,000 272,500 842,300
1 2 3 4 5 6 7 8
Miami silt loam Nappanee silt loam Nev/ton loamy fine sand Houghton Fincastle silt loam Crosby silt loam Cincinnati silt loam Chalmers clay loam
2 2 2 2 3 2 4 2
IV II VIII X II II IV VIII
Clermont silt loam
Frederick silt loam
11 12 13 14
Philo silt loam Zanesville silt loam Pox silt loam Bedford silt loam
1 4 2 4
III IV V III
Alford silt loam 3 Brookston silty clay loam 2
Pairmount silty clay loam 4
18 19 20 21 22
Parr silt loam Fox sandy loam Genesee silt loam Vigo silt loam Russell silt loam
2 2 1 4 3
Maumee fine sand
Till-mixed Till-Shale Outwash Marsh swamp Till-mixed Till-mixed Till-mixed Till-mixed
Upland Upland Terrace Terrace Upland Upland Upland Upland
Light Light Dark Dark Light Light Light Dark
Till-mixed Limey-Shale Residual-Cherty Limestone Alluvial Residual-Siltstone Outwash^mixe d Residual-Cherty Limestone Loess-mixed Till-mixed
’^Taken from "The Story of Indiana Soils", by T. M. Bushnell, Purdue
Benton Kosciusko Tippecanoe Clay I & II Putnam III Rush Starke
University, Agr . Sxp. Sta. Special Cir. 1, 1944.
culated and th.© following modification made:
removed by the plants had been calculated on the basis of an acre six inches using the volume weight as calculated from adding soil to all cans used in the greenhouse to equal height with apparently equal tamping.
This did not
appear to be a very reliable measure of volume weight; therefore, it was considered desirable to recalculate all data on the basis of 2,000,000 pounds per acre with the exception of the muck sample which was calculated on the basis of 760,000 pounds per acre.
These changes were made
and the recalculated data on supplying power listed in Table 2.
Also listed on Table 2 are several additional
chemical properties of the soil samples. Samples Used in the Investigation of Chemical Methods All samples used, except as noted, were taken from the bulk storage cans.
These samples had been stored for
approximately two years at the beginning of this investiga tion and had apparently kept in good condition.
samples NO. 4 and 16 had a musty odor associated with soils stored for long periods. Potassium Analysis All potassium analyses were made using the internal 'v
standard procedure on the Perkin-Elmer flame photometer. Model No. 52-A.
Notes and comments on the technique used
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fixation, hitric acid was selected as the most desirable extractant for future studies on exchangeable potassium. The six per cent hydrogen peroxide treatment did not bring out any marked relationships to the supplying power in this study.
This treatment by no means removed all of the
organic matter in the samples; therefore, it was thought that perhaps complete removal of organic matter might be desirable.
It may be noted by comparing the 0.2N nitric
acid extraction in Table 2 with the 0.2N nitric acid extraction in Table 3, that where the water soluble potassium was first removed, the sum of the water soluble and ex changeable was greater in every case than where the water soluble was not removed.
This suggested that if repeated
extractions were made with each extracting agent stronger than the previous, perhaps a correlation with the supplying power could be found.
The results of such a series of
extractions after complete removal of organic matter are presented in Table 4.
It appears that no more than a trend
is shown with the first four extracts and the range is not great enough to make a valid comparison.
The fifth extract
(the IN boiling nitric acid) is rather different; the differ ence between the high, low, and intermediate, is measurable and has possibilities for purposes of predictions.
centage-wise, the total potassium extracted by the five extractions does not appear as desirable as the fifth extraction (Table 4),
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With, these apparently encouraging results it seemed desirable to include all 23 soils in the next series.
had been little to indicate an advantage in the removal of or ganic matter and as it would be desirable to eliminate as many treatments as possible, this treatment was not repeated. In place of the weaker extractants, a stronger original extracting solution was used.
The first extraction was with
IN nitric acid at room temperature.
The residue was allowed
to stand in a moist state for four weeks and again extracted with IN nitric acid at room temperature.
The third ex
traction was with IN nitric acid boiled for 30 minutes and allowed to stand over night in the acid before filtering. Scatter diagrams of the results of these extractions plotted against potassium supplying power as determined by plants, are shown in Figures 1, 2, and 3.
In order that these results
may be compared with the usual exchangeable potassium. Figures 4 and 5 are also presented.
These compare the potassium
extracted with ammonium acetate and 0.2N nitric acid to the supplying power as determined by plants.
It is readily
apparent that the only extraction showing good comparison is with the IN boiling nitric acid treatment.
of the correlation coefficients listed in the figures show that the correlation becomes increasingly higher with the stronger treatment. The inadequacy of the test for exchangeable potassium as a means of evaluating the potassium supplying power of Indiana
0.7633 I.5865 I83
200 04 03
ACI D E X T R A C T
Ttie nonexciiangeable potassiian removed by plants compared to that removed by IN nitric acid.
g O CL
200 23 2*3
M I N U T E S BOILING
m in u t e s
(a) ratio 1 gm soil 10 cc acid
(b) ratio 1 gm soil 2 cc acid
b o il in g
The effect of boiling time on the extraction of potassinm at given soil-acid ratios.
45 minutes, as slight variations in time would cause less error in the amount extracted.
Figures 7(a) and 7(h), which show
the effect of ratio, indicate that a ratio of 1 to 2 is as critical concerning ratio as the ratio 1 to 10 was concerning time.
By extrapolating one would surmise that a time of
boiling and ratio could be found in which both were relatively Insensitive to slight variations; however, the amount ex tracted would, no doubt, be considerably above that removed by this crop and more cropping data with different crops would be needed in justifying the results. On the basis of these studies it was decided to use 10 minutes boiling time with a ratio of one gram of soil to 10 ml of IN nitric acid,.
Hereafter, in this manuscript,
reference to the potassium supplying power by chemical method will pertain to results obtained by this method. This is similar to the method used by Reitemeier (39) and was first suggested by Wood and De Turk (46).
of the literature revealed no fundamental justification for their (46) selection of this method.
Apparently it was
selected for the purpose of removing a part of the non exchange able potassium, and was later noted that the amount of the potassium removed was related to the potassium supply ing power under field conditions. It is a relatively simple matter to control the time of boiling; but where part of the soil or minerals are to be examined, a better knowledge of the mechanism involved
22 K 800
3 5^4 3
C O 400
SO IL-A C ID
1-4 1-2 SOIL-ACID RATIO
(b) 30 minutes boiling
The effect of soil-acid ratio on the extraction of potassium, at given boiling times.
is needed in order to be able to dboffise a ratio that will give the best results for comparative purposes.
may be duplicated with relatively high precision if a stand ard procedure is used concerning time of boiling.
found that results could be most easily duplicated if the hot plate were heated to about 180°C to start the boiling and then the controls reduced to give a temperature of about 140 to 150®C.
Time was measured from the beginning of
visable boiling. A scatter diagram which shows the potassium extracted by boiling 20 grams of soil with 200 ml of IN nitric acid for ten minutes compared to the potassium removed by eight harvests of ladino clover is presented in Figure
The correlation coefficient of 0.88 and the regression coefficient
of 0.81 is improved considerably by omitting
soils Nos. 4, 16, and 18, then these values become 0.96 and 0.92, respectively.
These three soils are high in
organic matter and perhaps vary considerably in their suitability for greenhouse conditions.
Soil No. 4, a
muck, was very fluffy, indicating that aeration had been excellent during the period of cropping.
Soil No., 16 had very
stable aggregation; the aggragates were not broken down in the determination of exchangeable potassium even after shaking the soil sample in the 1 to 2 suspension with 0.2N nitric acid for 30 minutes on a reciprocal shaking machine. On the other hand, aggregation in soil No. IB was completely destroyed by this treatment.
Hoffer (25), (25a) and others
have shown that potassium absorption by plants is influenced
c/> Iz < -I CL
MINOS SOILS NO. 4,16,18. r = 09600 b = 0.9216 Syx- 7 9
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The nonexchangeable potassium removed by plants compared to that removed by IN boiling nitric acid.
considerably by aeration.
The discrepancy of these soils would
bear this out; and it is possible that much of the variation in the other soils could be accounted for in this way, if accurate measurements could have been taken of the aeration conditions during the growth of clover.
Considering the many
sources of variation that are possible with data obtained in this manner, it is rather surprising that the error of estimate is no larger than 79 pounds per acre (soils 4, 16, and 18 omitted). Seasonal Effect upon Exchangeable Potassium and Potassium Supplying Power under Field Conditions It was suggested by Chandler, et al (10) that perhaps a measure of the seasonal change in exchangeable potassium from spring to fall could be used to give an indication of the supplying power.
This possibility was
investigated except that it was thought more desirable to measure the change from fall to spring.
Because of the
effect of drying noted by Attoe (2) and by Lee (31), the exchangeable potassium was measured both before and after drying. The data presented in Table 5, show that a trend appears to exist in the exchangeable potassium study especially on the dried samples; the soils with the higher supplying power give the greater increase in exchangeable potassium during the winter months.
1/ 1 /here
The change in the potassium status of several soils from fall to spring1
Exchangeable Percentage Potassium Percentage Potassium Change Change Supplying Power Dif . Pall Spring Fall Spring Dif. Samples Field Moist
130 60 130
90 150 140 60 140
3 23 5 5 5 6
30 10 0 10 10 10 10 0 100
12.5 25.0 7.7 0
7.7 9.1 9.1 7.1 0
160 380 380 480 510 540 570 600 700 1170
140 370 380 480 550 550 630 590 740 1250
0 -20 -10 0 0
12.5 2.7 0 0
7.8 1.9 10.5 1.7 5.7 7.0
Samples Dried 70^0 3 23 5 5 6 6
90 150 150
170 140 240 190 190 290 260
30 10 20 20 20
25.0 7.1 20.0
13.3 16.7 14.3 26.7
150 380 400 500 520 470 590 540 770 1050
^All values reported as Pounds KgO per
360 400 520 520 520 560 550 760
—2 0 0 20 0
50 -30 10 -10
4.0 0 10.6
5.1 1.9 1.3 14.3
,0 0 0 , 0 0 0 pounds of soil.
potassium was determined on the moist samples, the trend is much less apparent.
It is interesting to note that soil
No. 18, which gave low results with the greenhouse method but tested high by the chemical method, indicates a con siderable increase in exchangeable potassium during those months.
In comparison, soil Ho. 16 which tested medium
by the chemical method, but high by the greenhouse method, would indicate medium by the increase from fall to spring, on the dry sample and low on the moist sample.
words, the results agree better with the chemical method for determining potassium supplying power than with the greenhouse method.
This is in spite of the fact, that these
samples were not taken at the same locations as those used in the greenhouse study and for chemical determinations of potassium supplying power.
The supplying power analysis
show slight variation between fall and spring. gave an increase of about
Soil Ho. 20
pounds per acre in addition
to the 50 to 90 pound increase in exchangeable potassium. The lower supplying power samples failed to show an appreciable change.
The percentage variation in the potassium
supplying power data is rather small compared to the percent age variation in the exchangeable potassium with season. This demonstrates that the potassium supplying power as determined by the chemical method is little affected by seasons of the year and hence is a more reliable value than the exchangeable potassium.
It should be noted that the potassium supplying power of these samples were approximately the same, for the corresponding soil series, as those used in the previous study though they were taken at different locations.
These results indicate
that the change in exchangeable potassium from fall to spring could be used as an indication of the soils supplying power as was predicted by Chandler, et.al. (1 0 ):, but the amount of potassium extracted by IN boiling nitric acid gives a more reliable measure. Effect of Dvph: "prying at 70®C before Removal of Exchangeable Potassium The fall and spring samples afford an excellent opportunity to observe the effect of drying on the amount of exchangeable potassium extracted.
The data in Table 5 is
rearranged to facilitate a comparison of moist and dried samples in Table
The fall samples, with the exception of
soil No. 23, gave an increase in exchangeable potassium on drying.
This increase ranged from 0 to 40 pounds per acre for
exchangeable potassium and power.
for potassium supplying
Drying resulted in a greater release of potassium
from the spring samples than from the fall samples, except for Nos. 3, 18, and 23.
Nos. 2 and 23 were low in exchange
able potassium and had the lowest potassium supplying power of the group.
No. 18 was the soil with the highest exchange
able potassium, and the second highest supplying power. This would Indicate that the potassium in the two forms of
The effect of oven drying at 70®C on the exchangeable potassium*
Exchangeable KgO Percentage Potassium Percentage Moist Dried Dif. Change Supplying Change Power‘d (Chem ical) ■ ____________ Moist Dried Dif.___________ Pall Samples 80
130 60 130
3 23 5 5 5 6
10 0 10
20 10 100 10
50 30 40
7.6 66.7 15.2 9.1 91.0 7.1 41.7 15.7 30.8
160 380 380 480 510 540 570 600 700 1170
150 380 400 500 520 470 590 540 770 1050
-10 -10 0 20 20 10
4.3 6.2 0
5.3 4.2 2.0
Spring Samples 3 23 5 5 5
90 150 140 60 140
16 22 8
90 150 150
0 0 10
170 140 240 190 190 290 260
7.1 21.4 15.8
140 370 380 480 550 550 630 590 740 1250
360 400 520 520 520 560 550 760 1200
0 —2 0 -10 20
40 -30 -30 -70 -40 20
14.4 2.7 5.3 8.3 5.5 5.5 11.1 6.8
^ All values reported as pounds KgO per 2,000,000 pounds of soil
and 23 were about in equilibrium and release
was very low; whereas, the potassium in soil No. 18 was in such a loosely held state that equilibrium was reached in a period of a few months.
The other soils required
longer periods of time to reach equilibrium.
drying— which would come with cultivation and dry weather— is necessary to causéean equilibrium to be reached.
potassium supplying pov/er was only slightly affected by drying ; the percentage change on drying was small in comparison with the percentage change in the amount of exchangeable potassium. If this is a representive picture of what happens in the soil under cropping, and if a measure of the potassium status is to be had from the exchangeable, the sampling should be done in the spring and the samples thoroughly dried before the analysis is made.
If sampled at other
times, information such as the supplying power by chemical determination and fertilizer treatments would need to enter into an interpretation of exchangeable potassium..
data demonstrate the superiority of the potassium supplying power chemical determination over the measurement of exchangeable potassium as a means of appraising the true potassium productivity status of Indiana soils.
Effect of Previous PeiJtilizer Treatments on Exchangeable Potassium and Potassium Supplying Power of Soils Wood and DeTurk (46) found that the ”staying power" was little affected by past potassium fertility treatments* This is in opposition to the findings of Reitemeier, et* al. (39), who observed considerable effect of previous treatments Three different Indiana soil series were sampled to investi gate this factor.
Table 7 shows that the two sites which
were low in potassium supplying power, and had been in the rotation series, were practically unaffected by the fertiliz er treatment received over the past 20 to 30 years.
soil with the higher supplying power, that had been in alfalfa for 30 years, indicated some effect of past fertilizer treatments*
The results were not altogether
the expected, as the plot receiving lime alone and the untreated plot were found to have a higher supplying power than those receiving potash.
However, as might be expected,
the reserve potassium had apparently been reduced to the lowest level on the plot receiving lime and phosphate. These data indicate that soil management has not seriously affected the potassium supplying power on any of the plots. It would be desirable to study the soil from plots which had received high applications of potassium over a period of years.
These plots had only received additions about
equal to the potassium removed by plants, and thus they served more to illustrate the effect of cropping than
Effect of previous fertilizer treatment on the present exchangeable potassium and potassium supplying power.^
Treatment (per rotation)
Exchangeable Potassium Field Moist Dried 70®C
Clermont silt loam rotation plots 23 years no treatment no treatment manure, lime 400 lbs. 2 -1 2 - 1 2 lime, 400 lbs. 0-12-0
127 107 181 78
180 180 — —
180 160 150 160
620 550 480 500
F incastle silt loam rotation plots 30 years manure, lime and phosphate 60 manure, 1 ime, phosphate, and potash 130 Brookston silt loam Continuous alfalfa 30 years lime no treatment lime and phosphate lime and potash 1 ime,pho sphat e and potash
Potassium Supplying Power (Chemical)
90 80 80
"All values are reported in pounds KgO per 2,000,000 pounds soil,
the effect of potassium fertilization.
The level of
exchangeable potassium has been affected, in all cases, as was expected. Influence of Degree of Calcium Saturation on the Increase in Exchangeable Potassium from Drying of Brookston Silty Clay Loam A suitable explanation has not been offered for the mechanism that brings about an increase in exchangeable potassium in some soils on drying.
It has been suggested
that the exchangeable hydrogen replaces some of the fixed potassium at very low moisture contents.
was borne out when no increase occurred following the addition of a concentrated sodium salt solution to a soil and then evaporating to dryness. (31) In the alfalfa series of Table 7, it was observed that the increase in release occurred on the lime plots to approximately the same degree as on the unlimed plots. This would tend to discredit the hypothesis that the exchangeable hydrogen is an important factor, assuming that sufficient lime had been added to appreciably decrease the percentage of hydrogen saturation.
this further, a series of flasks was prepared with different amounts of calcium, hydroxide added. in Table
The results are shown
From this experiment, it would appear that the
degree of calcium saturation has no effect on the increase
Effect of added increments of calcium hydroxide on the increase in exchangeable potassium from drying Brookston silty clay loam.^
Treatment per 50 grams of Moist soil
m.e. Ca. added per 1 0 0 grams
Exchangeable EgO lbs./a .
Dried from field moist conditions
Dried from 200 ml HgO
Dried from 25 ml GaCOH)^^ 175 ml EgO
Dried from 50 ml Ga(OH)o 150 ml EgO
Dried from 100 ml Ca(OH)p 100 ml EgO
Dried from 200 ml CaCOH)^
^Exchange capacity of this soil is 50 m.e,/lOO grams, the moist content was 2 2 .0 %. ^Ca(OH)o = 0.04N.
in exchangeable potassium from drying the soil.
difference obtained between the sample dried from water suspension and dried from the field moist sample is unexplained.
The fact that there was no difference between
the samples dried from distilled water and dried from various increments of calcium hydroxide indicates that it was not due to the calcium present. These results are in agreement with those obtained by Lee (31) except in the conclusion drawn.
he did not run accheck with water added to the sample and thus concluded that replacement of hydrogen ions on the exchange complex by the added cation was responsible for the lack of increase in exchangeable potassium on drying.
In this study it was seen that the dilution treat
ment rather than the cation added reduced the release of potassium to the exchangeable form on drying. Effect of the Removal of Free Iron Oxides in Soils on Release of Exchangeable Potassium Bray and DeTurk (8 ) suggested that the source of the potassium which is not exchangeable, but becomes available as the exchangeable is removed, might be in the partly weathered edges of primary silicates.
in supplying power would not be indicated by the mineralogical composition.
The method proposed by Jefferies (27)
for the removal of free iron oxides has been found to
"clean up" the primary particles so that they are easily identified in pétrographie studies.
This treatment should
then remove at least a fraction of these partly weathered edges and thus force the potassium into exchangeable positions.
The effect of the removal of free iron oxide
on the exchangeable potassium of ten soils subjected to this "clean up" treatment is shown in Table 9.
While the in
crease in exchangeable potassium ranged from
per cent, there does not appear to be a relation between the additional amount of exchangeable potassium removed by this treatment and the potassium supplying power as determin ed in the greenhouse.
If the partly weathered edges of
primary minerals are involved, this process does not break down these edges sufficiently for the release of potassium to the exchangeable form.
However, it is
recognized that caution must be exércised in drawing conclusions from this method*
From Table 4 it was seen that
by removal of the organic matter considerable amount of exchangeable potassium was released to the water soluble form and some nonexchangeable potassium was released to the exchangeable.
With this upset in equilibrium it would
be possible for fixation to occur especially following the removal of the free iron oxide.
Therefore, the potassium
released by this latter treatment is only one of several reactions involved. Chemical Analyses of Soil Fractions Since it was established in this research that the
Effect of removal of free iron oxide on the exchangeable potassium of soils.
Exchang eable KgO before Removal of free iron oxide
1 2 6
340 165 280 235 250 85
15 17 20 22
Exchange able Increase from EgO after Removal of free Removal of fjgee iron oxide iron oxide*
240 295 275 135 470 205 490 320 285 160
^All values reported in pounds EgO per
Potassium Supplrying Poweapr (plahts)
300 640 530
35 130 40
85 35 80
,0 0 0 , 0 0 0 pounds of soil.
^Thls value includes any increase in exchangeable potassium resulting from the removal of organic matter as well as that released by the process used in the removal of free iron oxides
supplying power is a characteristic of each soil type, it seemed desirable to locate the source of this potassium that determines the potassium supplying power, the hypothesis was formulated that certain soil separates would be more important than others.
If this fraction could be located,
then, perhaps by x-ray analysis, the mineral or minerals responsible for the variation in soils could be identified. Table 10 is a record of the weights of the different fractions of one group of eight soils in which the silt was separated from the coarse clay at 0.005 mm. effective diameter, Table 11 is a record of the weight of the different fractions of another group of eight soils in which the fraction 0.005 mm. to
mm. was separated from the coarse clay and silt.
This difference in the point of fractionation was the result of a misprint in the printed procedure followed in the first fractionation.
The error was found before the second group
was fractionated and the additional size range was separated. As may be seen in Figure 9, this fraction is more nearly like the coarse clay by chemical extraction with INHNO5 than the silt, therefore,the error was of little consequence. To facilitate comparisons, this fraction (0.005-0.002) was calculated into the 0.005-0.001 ram. fraction in Figure 10, which lists the fractions in decreasing order of the total soil supplying power.
This figure shows that the soil
fractions do not adhere strictly to the order of the supplying power of the total soil, but there is a definite trend which
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Intensity of diffraction at this angle. X-ray Analyses of Fine Sand Fraction (0.05 to 0.02 imri. ) The x-ray diSPraction patterns of the 0.05 to 0.02 mm. fraction of 16 soils are shown in Figures 13 (a) through 13 (p).
The peaks at 26.3, 30.5, and 33.7 degrees for 20
are the peaks for quartz and for all of these samples, this is the major constituent.
The peaks that occur from 34.7 to
35.3 degrees are attributed to microcline, since it is the most resistant of the feldspars to weathering.
to Table 12, it is seen that the amount of potassium ex tracted from microcline by the acid treatment is less than that from the other minerals.
From the potassium supplying
power of the fractions. Figure 10, little variation in the potassium containing minerals was expected. patterns bear this out.
Since microcline is known to be
one of the most resistant of potassium minerals, one would not expect slight variation in the amount of this mineral in a fraction to have a pronounced affect on the potassium supplying power. Attention is called to the rapid rise in background that occurs between 13 and 11 degrees and between
and 4 degrees.
In this case the background is practically identical to the background obtained with quartz. Figure 12 (e), and should not be confused with illite.
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was present in tlie lilgiiest percentages in tîie
Feldspars and muscovite were apparently not
mm with possibly one or two exceptions.
Illite, mica-intermediates and montmor il Ionite occur through out the clay fraction and are almost the only crystalline material in the less-than-O.0002 mm fraction.
in mineralogical composition with particle size is in close agreement with the findings of Jackson et al. (26a).
area under the illite peak was measured, using the same technique as was used with the medium clay fraction.
areas are plotted against the potassium supplying power of the fraction in Figure 21.
The correlation coefficient of 0,82
is less than that for the medium clay and the standard error of estimate, 17.2 per cent, is greater.
Since muscovite was
not expected to occur in the fine fraction, the peak at degrees should be accounted for entirely by illite.
it was anticipated that the highest correlation would occur in this fraction if illite was the source of most of the potassium supplying power.
It was very difficult to define the boundaries
to the peak caused solely by illite, because of the low amplitude of thé peak and the high background, accompanied by the second order peak for montmor ill oni te on one side and micaintermediate on the other, For this reason the variation could easily have been the result of error in measuring the area under the peak rather than actual variations in the amount of illite present.
This emphasizes the need for a study of
=0.05 ol7 08
POWER (CHEMICAL) PER
The relative intensity of reflection from 0 0 1 crystal plane at 9.9A spacing for one per cent suspension.
methods so that better defined peaks with less background may be obtained. X-ray Analyses of Clay Fractions Using a Two Per Cent Suspension in Preparing the Slide It was observed that the mounts prepared from one per cent suspensions were very thin, especially with the fine clay fraction (less-than-O.0002 mm).
This suggested that
perhaps more satisfactory results could be obtained if the mounts for x-ray analyses contained a thicker layer of clay.
There was also the possibility that another set of
treatments of the samples might yield better patterns. Preliminary studies were undertaken to explore these possibilities. X-ray Diffraction Patterns of Mounts Prepared from Two ^63?^ Cent Suspensions Compared to Those Prepared from One ^ r Cent Suspensions To investigate the possible advantage in having a thicker layer of clay on the mounts, two per cent suspension of seven samples of the fine clay fraction (less-than-0.0002 mm) were prepared.
patterns. Figures 22 (a) through 22 (g), show a definite strengthening of the diffraction intensities when compared to Figures 20 (a, b, d, t, h, n, o) respectfully.
difference in height of the three potassium supplying power levels give a visual difference in height of the curves at 11.2 degrees.
In patterns such as these, the area under the
curve due to illite alone cannot be measured accurately with
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