EXEEREEENT seevzee LEBRARY
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' A75-V1228-5,0OO-L18O

TEXAS AGRICULTURAL EXPERIMENT STATION

A. B. CONNER, DIRECTOR
COLLEGE STATION, BRAZOS COUNTY. TEXAS

BULLETIN NO. 391 JANUARY, 1929

DIVISION OF CHEMISTRY

Relation of the Water-Soluble Potash, the
Replaceable, and Acid-Soluble Potash
t0 the Potash Removed by Crops
in Pot Experiments

 

AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS
T. O. WALTON, President

STATION STAFFT

  
   
      
  
   

ADMINISTRATION: VETERINARY SCIENCE:
A. B. CoNNER, M. S., Director *M. FRANcis, D. V. M., Chief
R. E. KARPER, M. S., Vice-Director H. SCHMIDT, D. V. M., Veterinarian
J. M. ScRAEDEL, Secretary F. E .CARRoLL, D. V. M., Veterinarian 
M- P- H°LLE"AN»J'R-- Chi‘? 5'8"‘ PLANT PATHOLOGY AND PHYSIOLO
J. K. FBANCKLOW, Assistant Chief Clerk J J TAUBENHAUS Ph D Chief 
CREsTER Hiccs, Executive Assistant   EZEKIEL pf, D’ pjan, Pathohgm '
C. B. NEBLETTE, Technical Assistant ' Laboratory ‘Tecbnigl-an 
CHEMISTRY‘ . W J BACH M S Plant Pathologist
G. S. FRAPs, Ph. D., Chief; State Chemist J PA,“ LvéK   Plant Patholagist
ls;-  ‘ézifiigzgjlzMB- SS» Aézgrlgg Chemist B. F. DANA,  ‘S., Plant Pathologist
WALDo H. WALKER, Assistant Chemist FARM AND RANCH ECONOMICS‘
VELMA GRAHAM, Assistant Chemist L- P~ GABBARD’ M~ s“ hlef . -
H. S. 056001), M. S., Assistant Chemist W- E- PAUISQN’ Ph- D-v Marketing Re“
T. L. OGIER, B. S., Assistant Chemist Spec‘ ‘s’ "f
i. G. EVAIES, Assistant Chemist _ C- Akggaiilglhlig-l) Farm M ""00""?! y
THAN J. TERGES, B. S., Assistant Chemist V. L. CORY, M. s" Grazing Research B“ 

G.S.C ,A.B.,A 't tCh 't .
JEANNERIII/IISFGIEVGAS. Assisidhst ‘glhemifiinls _ J:  B- S» Asswlant; Farm R5” 
ug§¥fc%'“f{§ff{§f' M’ Se" Assistant Chemist "J. N. TATE, B. S., Assistant; Ranch R -- I

HAMILTON P. TRAuE, Ph. D., Chief and Account’
H. NEss, M. S., Berry Breeder RURAL HOME RESEARCH: _
RANGE ANIMAL HUSBANDRY: JEssIE WHITACRE, Ph. D., Chief
J. M. JoNEs, A. M., Chief; Sheep and Goat IVIAMIE GRIMEs, M. S., Textile and Clot
Investigations Specialist __
J. L. LUSH, Ph. D., Animal Husbandman; EuuA E. SuuNER, M. S., Nutrition Specia , -
Breeding Investigations SOIL SURVEY: '
STANLEY P. DAvIs, Wool Grader . **W. T. CARTER, B. S., Chie
ENTOMOLOGY: E. H. TEMPLIN, B. S., Soi Surveyor
F. L. TIIoMAs, Ph. D., Chief; State T. C. REITcII, B. S., Soil Surveyor
Entomologist _ L. G. RAosDALE, B. S., Soil Surveyor
H. J. REINIIARD, B. S., Entomologist BOTANY: _
R. K. FLETCHER, M. A., Entomologist H. NEss, M. S., Chief
W. L. OWEN, JR., M. S., Entomologist SIuoN E. WOLPP‘, M. S., Bolanist
FRANK M. HULL, M. S., Entomologist SWINE HUSBANDRY:
J. C. GAINEs, JR., M. S., Entomologist FRED HALE, M. S., Chief
C. J. TODD, B. S., Entomologist DAIRY HUSBANDRY: »..
F. F. BIBBY, B. S., Entomologist O. C. COPELAND, B. S., Dairy Husbandman -
S. E. McGREcoR, JR., Acting Chief Foulbrood POULTRY HUSBANDRY: _ ..
Ins ector R. M. SHERWOOD, M. S., Chief
Orro ACKENSEN, Foulbrood Inspector ***AGRICULTURAL ENGINEERING:
AGRONOMY: MAIN STATION FARM:
E. B. REvNoLDs, M. S., Chief G. T. McNEss, Superintendent
R. E. KARPER, M. S., Agronomist; Grain Sor- APICULTURE (San Antonio):
(ghum Research _ H. B. PARKS, . S., Chief
P. . IVIANGELSDORF, Sc. D., Agronomist; A. H. ALEx, B. S., Queen Breeder
in charge of Corn and Small Grain I nvesti- FEED CONTROL SERVICE:
ations F. D. FULLER, M. S., Chief
D. . KILLovcR, M. S., Agronomist; Cotton S. D. PEARcE, Secretary
Breeding _ J. H. RooERs, Feed Inspector
H. E. REA, . S., Agronomist; Cotton Root Rot W. H. W000, Feed Inspector .
Investigations K. L. KIRKLAND, B. S., Feed Inspector .
W. E. FLINT, B. S., Agronomist W. D. Nonrncun, JR. B. S., Feed Inspector "I
PUBLICATIONS: SIDNEY D. REvNoLDs, JR., Feed Inspector
» A. D. JAcKsoN, Chief P. A. M0oRE, Feed Inspector
SUBSTATIONS
No. I, Beeville, Bee County: No. 10, Feeding and Breeding Station. near
R. A. HALL, B S., Superintendent Colle e Station, Brazos County:
No. 2, Troup, Smith County: R. M. IIERwooD, M. S., Animal Husband-
P. R. JoiINs0N, B. S., Act. Superintendent man in Charge of Farm
No. 8, Angleton, Brazoria County: L. J. McCALL, Farm Superintendent
3' H STANSEL’ M- S“ Supumteniem No. l1, Nacogdoches, Nacogdoches County:
No. 4, Beaumont, Jefierson County: H_ F_ MORRIS’ M_ S“ Supen-ntendent

R. H. WYCHE, B. S., Su erintendent , _

Nm 5' Temple, Be" Coma“ **No. 12, Chillicothe, Hardernan County:
HENRY DUNLAVY, M. S., Superintendent ‘Ml R- UINBY’ B‘ s“ superlnt§ndenl .
3_ p DANA M_ S“ plan; pathologist J. C. TEPHENS, M. A., Junior Agronomist
H. E. REA, B. S., Agronomist; Cotton Root Rot No. l4, Sonora, Sutton-Edwards Counties: 1

Investigations W. H. DAuERoN, B. S., Superintendent
SIuoN E. WOLFE, M. S., Botanist; Cotton Root E. A. TUNNICLIFF, D. V. M., M. S.,
Rot Investigations Veterinarian _
No. 6, Denton, .Denton County: V. L. CORY, M. S., Grazing Research Botanist 1
P. B. DUNKLE, B. S., Superintendent "O. G. BABCOCK, B. S., Collaborating fa
No. 7, Slgur, Dickens County: Entomologist . 1
R. E. ICKSON, B. S., Superintendent O. L. CARPENTER, Shepherd
W. E. FLINT, B. S., Agronomist No. 15, Weslaco, Hidalgo County:
No. 8, Lubbock, Lubbock County: W. H. FRIEND, B. S., Superintendent
D. L. JoNEs, Superintendent SHERMAN W. CLARK, B. S. Entomologist
FRANK GAINEs, Irrigationist and Forest W. J. BAcR, M. S., Plant Pathologist
Nurseryman No. 16, Iowa Park, Wichita County:
No. 9, Balmorhea, Reeves County: E. J. WILsoN. B. S., Superintendent _
J. J. BAvLEs, B. S., Superintendent J. PAUL LUSK S. M., PIGIIIPQIIIOIOQISI

Teachers in the School ot‘ Agriculture Carrying Cooperative Projects on the Station:

W. ADRIANcE, M. S., Associate Professor of Horticulture

. W. BILSING, Ph. D., Professor of Entomology

. P. LEE, Ph. D., Professor of Marketing and Finance

D. SCOATES, A. E., Professor of Agricultural Engineering

H. P. SMITH, M. S., Associate Professor of Agricultural Engineering
R

A

<wga

H. WILLIAMS, Ph. D., Professor of Animal Husbandry
. K. MAcKEY, M. S., Associate Professor of Animal Husbandry
J. S. MooroRD, M. S., Associate Professor of Agronomy

TA-s-ot December 1,_ 1928. ‘Dean, School of Veterinary Medicine.
"In cooperation with U. S. Department of Agriculture.
"fin cooperation with the School of Agriculture.

SYNOPSIS

One part 0f the very complex problem 0f soil fertility is its
relation t0 the chemical composition of the soil, and this Bulle-
tin deals with a phase of this aspect of the problem. The
fertility of the soil in potash as measured by its capacity to
supply potash to crops in pot experiments is related to the
water-soluble potash, the replaceable potash, and the active
potash of the soil. The amount of potash taken up by crops
of corn and kafir or milo usually averages about one-half the
replaceable potash and five to six times the water-soluble
potash in the soil. The losses of potash from the soil by
cropping are reflected in the loss of the soil in water-soluble
potash and in replaceable potash. The amount of potash re-
moved by the crops from the soil averages about 3 to 16 times
the water-soluble potash lost in cropping and about twice the
replaceable potash lost in cropping. The active potash is still
considered the best measure of the ability of the soil to supply
potash to crops. ~ The differences between the amounts of
potash removed by a first and a second extraction of the soil
with nitric acid become greater as the potash taken up by
crops increases. Correlation coefficients for the factors studied
show close relations between them. Correction of the 0.2N
nitric acid for neutralization by the bases of the soil in the
estimation of active potash is not advisable.

CONTENTS

{w
n 

PAGE
Introduction . . . .' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51f
Method of Work...l......' . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. -
Water-soluble potash . . . . . ; . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . '7 
Relation of Water-soluble potash to potash removed by crops... 7 
Relation of the Water-soluble potash to the active potash . . . . .. 8 l‘
Effect of cropping on the Water-soluble potash . . . . . . . . . . . . .. 8 
Potash soluble in 12% hydrochloric acid . . . . . . . . . . . . . . . . . . . . . . . . 9' v
Relation of potash soluble in 12% hydrochloric acid to potash p
removed by crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 
Replaceable potash in the soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10 
Relation of the replaceable potash to the potash removed by A
crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 11 4-‘
Relation of potash removed by crops to the loss of replaceable 
potash in the soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 12 .
Discussion of results for replaceable potash . . . . . . . . . . . . . . . .. 13 c7
Relation of the loss in extraction of active potash to the loss in‘
cropping . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . 1a A
Relation of the loss in extraction to the potash in crops . . . . . . . 14 ' ‘

Effect of the neutralization of the basicity on the active potash and

relation to cropping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 15
Results of the Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 16
Summary of correlation coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . .. 17

Summary and conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 17

BULLETIN NO. 391 JANUARY, 1929

RELATION OF THE WATER-SOLUBLE POTASH, THE RE-
PLACEABLE, AND ACID-SOLUBLE POTASH TO THE
POTASH REMOVED BY CROPS IN POT
EXPERIMENTS

G. S. FRAPS

The relation of the chemical composition of the soil to soil fertility
is a fundamental and difficult problem of agricultural chemistry. Soil
fertility is the resultant of many factors; its relations are influenced
not only by the quantity of the various compounds present, and they by
one another, but by other conditions, such as the physical character and
conditions of the soil, and other variables such as moisture, temperature,
and bacterial action. Field results as measured by yields are influenced
by the factors just mentioned. and others in addition, such as the depth
of the surface soil, the depth of subsoil, and variations in the physical
character of the soil. Many soils are so variable that the difficulty of
sampling may so result that the samples taken do not represent the
field sampled, as has actually occurred.

The potential fertility of the soil, as such, must be distinguished from
the productiveness of the soil as measured by crop yields. The soil

may, for example, have a high capacity to supply potash to plants,"

varying, no doubt, to some extent according to the nature of the plant.
The crop grown, however, may not be able to take up the potash, owing
to the adverse operation of other factors, or, having taken it up, may
not be able to effect a corresponding production of grain or other crop,
due likewise to other factors. What applies to potash applies also to
phosphoric acid, nitrogen, and other factors of fertility; the power of
the soil to supply one or more of them is not necessarily reflected in the
yield of the crop. The ability of the soil to supply, and the power of
the crop to use, are two separate things, and must be considered
separately. This is an elementary principle of agricultural chemistry,
which seems, however, sometimes to be forgotten.

The fertility of a soil in any factor is here defined as the power of
the soil to furnish that factor, regardless of the ability of a crop to
utilize it. The author at present knows no better measure of the fer-
tility of a soil in potash than the amount of potash which crops can
remove from that soil under standard conditions. As crops vary in
their power to take soil potash, it is necessary also to select some definite
crop or to call attention to the fact that the results apply to the crops
selected under the conditions under which they were grown.

Some chemists have found little relation between the chemical com-
position of the soil and its fertility, but others have had better success.

6 BULLETIN NO. 391, TEXAS AGRICULTURAL EXPERIMENT STATION

It is evident that the factors of fertility must be studied separately, ;
both independently and in relation to one another, before they can be ,-

recombined to represent any particular soil complex.

Comparison of the chemical analysis of the soil with the results of pot 
experiments at the Texas Agricultural Experiment Station extending __'
over a number of years has shown that chemical methods for potash 
(Bulletins 145, 190, 384, 325, and 355), phosphoric acid (Bulletins
126, 1'78, 212, 267), and nitrogen (Bulletins 151, 259, 283) give results
that are closely related to particular plant food furnished by the soil .._'
in pot experiments. Chemical analysis cannot be used as an exact =12

measure of the fertility of soil in some particular plant food, but can

be used to divide the soils into groups within which other factors come j
into play and may have greater influence than the plant food studied. 
That is to say, with soils which differ to a decided extent in plant food, p '
we would also expect corresponding differences in their reaction to the ~

v plant food studied, not exact but approximate. Soils of the same group 

as regards a particular plant food may also differ in their reaction to 
plant food on account of the play of other factors, but these differences y
within the groups should be smaller than Without the groups. The a
fact must be emphasized that the quantity of potash in the soil is only 
one of the factors which influence the relation of the soil potash to the 
crop, and while it is important as regards soil fertility, the fact that the 

chemical content is only one factor must not be forgotten. v
Some of the methods tested are better adapted to the purpose than
others. The work is being continued for the purpose of testing addi-

‘ tional methods of analysis and for studying other factors which enter

into the problem.

Previous bulletins have shown that the active potash of the soil is the
best measure yet found of the ability of the soil to furnish potash to
crops in pot experiments. The object of the present bulletin is to dis-
cuss the "relation of some of the other forms of potash in the soil to the

potash furnished to crops. The water-soluble potash, the potash soluble

in 12 per centhydrochloric acid, the replaceable potash, and the potash
extracted by successive extractions with 0.2 N nitric acid are discussed,
as Well as the question of neutralizing the basicity of the soil in the
estimation of the active potash. This Bulletin is the sixth in a series
dealing with the potash of the soil, the preceding ones being Bulletins
145, 190, 284,325, and 355.

METHOD OF WORK

The pot experiments were carried out as described in Bulletin 325
and others. The quantity of soil used was 5000 grams, the pots were
kept in a greenhouse, and the first crop grown was usually corn, the
second kafir, or sorghum. The potash in the dried crop was estimated
in the usual Way. The results are presented in parts per million of
soil except when otherwise specified.

POTASH REMOVED BY REAGENTS AND BY CROPS 7

WATER-SOLUBLE POTASH

Investigators of the potash soluble in water in the soil have used a
variety of methods. The results have been used both for purposes of
investigation and for judging the ability of the soil to yield potash to
plants. The potash soluble in water at any given time may be in pro-
portion to the total amount soluble, but is less than the amount which
dissolves during the season of cropping. When potash is removed from
the solution by the plant, an additional amount probably enters into
solution, though the strength of the soil solution is not necessarily kept
constant. The rate at which the solution occurs would depend on the
nature of the material, the quantity of potash compounds present, and
other factors, and it would have an effect on the amount of water-
soluble potash furnished to the plant. The water extract of a soil, how-
ever made, does not necessarily represent the soil solution. The soil is a
mixture of particles of various kinds; the aqueous solution surrounding
a particle containing soluble potash may be quite different from that
surrounding a particle which absorbs potash. The water extract to a
certain extent must contain an amount of potash between the high and
low content surrounding the various particles.

Method of Analysis

Since the estimation of the amount of water-soluble potash can be
only relative and not absolute, the method used for its estimation was
arbitrary. It is described as follows:

Place 200 gm. of the soil in a bottle with 2000 c.c. water in a water
bath heated to 40° (l, and keep at 40° five hours. Shake every half
hour. Filter on a double fluted filter. Evaporate 1600 c.c. to about
100 c.c., filter and wash. Evaporate the filtrate nearly to dryness in an
evaporating dish, add 3 c.c. nitric acid and 8 c.c. hydrochloric acid,
evaporate to complete dryness, and heat for about 30 minutes at about
120° C. Take up with acid and water, and filter into an evaporating
dish. Evaporate the solution to dryness with 5 c.c. conc. hydrochloric
acid; take up with water and 2 or 3 c.c. hydrochloric acid; filter and
wash, if necessary. Add 2 c.c. platinum chloride and evaporate to
dryness. _ i

Let cool, add about 10 c.c. acid alcohol, and break up material by
stirring. Wash three or four times with about 10 c.c. acid alcohol by
decantation. If the potash salts appear to be pure, transfer to'a Gooch
with a new felt and wash about 8 times with 95 per cent alcohol. If
the precipitate is not clean, wash with ammonium chloride, using small
amounts, then with alcohol. Dry in a steam oven, and calculate to parts
per million water-soluble potash.

Relation of Water-Soluble Potash t0 Potash Removed by Crops

Table 1 contains the average results arranged by potash soluble in
Water. With the exception of the first group, the average amount of

Q

8 BULLETIN NO. 391, TEXAS AGRICULTURAL EXPERIMENT STATION

potash removed by the first crop and by two crops increases regularly
as the average amount of water-soluble potash extracted from the soil in-
creases, up to 48 parts per n1illion of water-soluble potash in the soil.
Beyond this point, the results are somewhat erratic, though the potash
taken up by the crop shows a tendency to increase as the water-soluble
potash in the soil increases. The amount of potash taken up by the first
crop averages three or four times as much as the water-soluble potash in
the soil. The amounts of potash taken up by the two crops usually
average 5 to 6 times as much as the water-soluble potash in the soil.

Table 1.—Potash in Parts Per Million of Soil Arranged in Groups by Water-soluble Potash.

\Vater- Water-
Potash Potash soluble soluble Active
Number Taken Up Taken Up Potash in Potash in Potash I
of Soils Group by First by Two Soil Before Soil After in Soil
Crop Crops Cropping Cropping

14 6-12 81 125 10 10 103
27 12 1-18 66 98 15 0 100
40 18 1-24 93 140 21 4 129
29 24 1-30 111 160 27 13 154
16 30 1-36 132 188 33 13 162
28 36 1-42 140 192 39 12 212
12 42 1-48 176 251 45 14 238
17 48 1—54 131 194 51 17 222
12 54 1-60 216 311 57 15 284
12 60 1-66 209 283 63 23 281
6 66 1-72 188 302 69 19 375
1 72 1-78 201 399 74 11 402
2 78 1-84 182 315 80 34 541
5 84 1—90 284 393 86 35 621
1 108 1—114 491 665 114 37 628
2 120 1-126 342 522 124 35 832
2 126.1—132 309 505 132 21 540
2 1621-168 393 569 164 42 1409

The correlation coefficient, r, for the potash in 2 crops and water-
soluble potash is —|— .703 i .022.

Relation of the Water-Soluble Potash to the Active Potash

Table 1 also shows the average active potash contained in the soils
on which water-soluble potash was determined. The active potash tends
to increase as the water-soluble potash increases, though the averages
are somewhat irregular. There is thus a relation between the active
potash and the water-soluble potash, as was to be expected.

The correlation coeflicient, r, for the water-soluble potash and the
active potash is ~—|— .789 —_I; .017. The correlation between the Water-
soluble potash and the active potash is closer than between the water-
soluble potash in the soil and the potash removed by crops.

Elfect 0f Cropping on the Water-Soluble Potash

The estimation of water-soluble potash in a soil before and after
cropping in the pot experiments frequently (though not always) shows
a decrease in water-soluble potash caused by cropping.

POTASH REMOVED BY REAGENTS AND BY CROPS 9

Table 1 gives the average Water-soluble potash before and after crop-
ping, which can be compared with the potash removed by two crops.
There is a loss of Water-soluble potash due to cropping but it is only a
small part of that removed by the crop, especially in the first group.

Table 2 compares the potash removed by the crops with the loss in
water-soluble potash and the loss in active potash from the soil before
and after cropping. The soils are averaged in groups according to the
potash removed in the crops, and the averages only are given. This is
a different arrangement from Table 1, which is arranged according to
the water-soluble potash in the soil. The loss in water-soluble potash
is, as could be expected, much lower than the potash removed by cropping
or than the loss in active potash. With the first groups the loss in
“rater-soluble potash averages about one-third the amount taken up by
the crop, but with the other groups the loss in water-soluble potash is
from 6 to 12 per cent of that removed by the crop.

Table 2.—Potash in Crops Compared with Loss of Active Potash and Water-soluble Potash
from the Soil in Parts Per Million.

Water- Water-
Loss_ of soluble soluble Loss
Number Group Potash Active Potash 1n Potash 1n Water-
of SOllS in Crops Potash Soil Before Soil After soluble
from Soil Cropping Cropping from Soil
11 0-50 42 16 28 13 15
34 51-100 80 32 21 12 9
72 101-200 151 61 30 14 16
47 201-300 240 95 37 15 22
22 301-400 352 169 47 15 32
10 401-500 457 201 54 20 34
12 501-600 546 275 74 19 55
12 601-700 633 241 55 17 38
2 801-900 884 607 101 36 65
1 901-1000 934 549 124 35 89

POTASH SOLUBLE IN 12 PER CENT HYDROCHLORIC ACID

In some European countries the potash in the soil is estimated by
extraction with 12 per cent hydrochloric acid at room temperature.

The following method of analysis was used in the work here reported:

To 900 c.c. hydrochloric acid C. P. add 1800 c.c. water, make 20 c.c.
up to 200 c.c. and titrate 10 c.c. With 0.1 N ammonia. Make up so
that 10 c.c. (1 1 c.c. of acid) I 33.3 c.c. 0.1 N ammonia. This acid
is 3.33 N. Digest 10 grams soil for 24 hours with 100 c.c. of the above
hydrochloric acid at room temperature, shaking occasionally. Filter and
wash with hot Water. Add 1 c.c. nitric acid. Evaporate to dryness
and heat on steam bath to render silica insoluble. Take up with hydro-
chloric acid and hot water, filter and wash. Evaporate to about 20 c.c.
Add 5 c.c. platinum chloride solution, and evaporate to a paste, or to
dryness if possible. Let cool. Add 10 to 30 c.c. acid alcohol With
stirring (10 c.c. concentrated hydrochloric acid to 100 c.c. alcohol 95
per cent). Pour 01f the alcohol through a Weighed Gooch crucible and

10 BULLETIN NO. 391, TEXAS AGRICULTURAL EXPERIMENT STATION

wash again with the acid alcohol. Then Wash with 95 per cent alcohol
by decantation until no colored material is dissolved. When the col-
ored material has been Washed out—not less than 8 Washings—pour on
10 c.c. ammonium chloride solution and allow it to stand a few minutes
to dissolve the impurities. Pour off the wash liquid through the Gooch
crucible, and repeat the Washing three times or more if necessary to
remove all white material or other foreign material from the platinum
precipitate. Then wash the potash salt into the Gooch crucible with 95
per cent alcohol and Wash eight times with alcohol. Dry for an hour
or more in the steam oven, cool in desiccator, and Weigh.

Relation 0f Potash Soluble in 12 Per Cent Hydrochloric Acid to Potash
Removed by Crops

Table 3 contains the average results of the analyses arranged accord-
ing to the potash soluble in 12 per cent hydrochloric acid. The potash
in the crops increases with the potash soluble in 12 per cent hydrochloric
acid up to about .075 per cent, after which it is irregular. The active
potash in the soil increases in a similar Way. The potash soluble in 12
per cent acid is about twice the active potash up to .044 per cent acid-
soluble potash or 185 parts per million of active potash, after which it
is usually three times as much, though sometimes much more.

Table 3.—Potash in Parts Per Million of Soil grrémged by Percentages of Potash Soluble
' 2% ci .

1n 1
Potash Soluble _
Potash in Potash in in 127 Acid Active Potash

Number Group First Crop Second Crop in goil 1n Soil

Averaged Per Cent Per Million Per Million Per Cent Per Milllon
5 . . . . . . . . . . . 0- 01 32 54 O07 57

30 . . . . . . . . . . . 0101- O2 59 79 016 83

47 . . . . . . . . . . . 0201- 03 101 137 O29 149

36 . . . . . . . . . . . 0301- O4 125 168 035 165

2O . . . . . . . . . . . 0401- O5 133 190 044 185
15. 0501- 06 145 216 O55 220
11 . . . . . . . . . . . 0601- O7 180 261 064 287

11 . . . . . . . . . . . 0701- 08 202 312 075 303

10 . . . . . . . . . . . 0801- 09 192 289 085 253

8 . . . . . . . . . . . 0901- 10 209 334 097 306

9 . . . . . . . . . . . 1001- 11 270 374 109 329

5 . . . . . . . . . . . 1101- 12 249 383 115 272

3 . . . . . . . . . . . 1201- 13 307 368 124 444

8 . . . . . . . . . . . 1301- 14 235 361 134 342

2 . . . . . . . . . . . 1401- 15 277 442 142 402

3 . . . . . . . . . . . 1601- 17 256 348 165 515

1 . . . _ . . . . . . . 1801- 19 144 304 186 561

2 . . . . . . . . . . . 1901- 20 342 522 199 832

1 . . . . . . . . . . . 2201- 23 126 162 227 256

The correlation coefiicient, r, for the potash in two crops (227 tests)
and the potash soluble in 12 per cent acid is ~—|— .720 i .022.

REPLACEABLE POTASH IN THE SOIL

It has been known for many years that portions of such bases in the
soil as calcium, magnesium, or potassium could be replaced by other

. -1.“ n“

POTASH REMOVED BY REAGENTS AND BY CROPS 11.

bases. This phenomenon of fixation was extensively studied by Way and
others about 1860 (Fraps’ Principles of Agricultural Chemistry, p. 234).
In recent years the subject has been given renewed attention, and studies
under the name of base exchange have given some very significant re-
sults, especially in relation to alkali soils and the cause of the difficulty
of reclaiming them by leaching (Kelly and Brown, Soil Science 20,
473). Soils in which the replaceable calcium and magnesium have
been replaced to a large part by sodium, run together easily, which
causes the penetration of water to be very slow. Replacing the sodium
by calcium makes the soil more permeable and more easily penetrated
by water.

Thereplaceable potash in the soil can be estimated by means of treat-
ment with a strong solution of ammonium chloride and repeated wash-
ing with the same solution. The method used is based on that de-
scribed by Hissink (Soil Science 15, 269).

Dissolve 365 gm. ammonium chloride in ten liters of distilled water.
Weigh 24.23 grams of soil into a beaker, add 100 c.c. ammonium chloride
solution and stir well. Let stand over night. Filter into a 500 c.c.
graduated flask and wash to volume with ammonium chloride solution,
allowing all the liquid to pass through before adding fresh portions.
Evaporate to about 7 5 c.c., put in a deep beaker, and slowly add a mix-
ture of 20 c.c. conc. nitric acid and 4 c.c. hydrochloric acid. Evaporate

_ to dryness and take up with 10 c.c. hydrochloric acid and 2 c.c. nitric
acid. Again evaporate to dryness. Take up in a little hydrochloric
acid and water, filter and wash, add platinum chloride solution, and

. complete as for potash in soils.

Relation of the Replaceable Potash to the Potash Removed by Crops

Table 4 contains the results of the work arranged according to the
s‘ replaceable potash. The potash removed by the crops increases with
 the first groups, then becomes somewhat irregular, with a tendency to
 increase as the potash soluble in ammonium chloride increases. The
i replaceable potash is greater than the active potash. The active potash
E increases with the potash soluble in ammonium chloride, though not as
x rapidly; so there are greater differences between the two when the soils
' are high in replaceable potash than when they are low.

 The correlation coefficient, r, for the replaceable potash in the soil
' and the potash removed by two crops is —l— .910 i .012.

 The correlation coefficient, r, between the replaceable and the active
 potash is + .879 i .016.

_ In similar work on active potash, the correlation coeificient for active
 potash in the soil and the potash removed from 2'71 soils in pot experi-
ments, r, is + .794 i .014. However, when the correlation was cal-
 culated for the active potash and the potash removed by crops for the-
~r same 88 soils used for replaceable potash, the correlation coefficient was:
2, + .886 i .015. There is thus little difference between the correlation

  
   
 
  
   

12

coefficients for the replaceable potash and for the active potash. From;
a laboratory standpoint, the estimation of active potash is t0 be preferred. i

Table 4.—Relation of Replaceable Potash to Potash Removed b

in Parts Per Million 0f Soil.

BULLETIN NO. 391, TEXAS AGRICULTURAL EXPERIMENT‘ STATION

y Crops and to Active Potash

Group
Number According to Potash in l Potash in Replaceable Active Potash
Averaged Replaceable First Crop Two Crops Potash in in Soil
Potash Soil
1. . 501-75 26 40 68 35
2. . 75.1-100 36 53 77 60
17.. 100. 1-125 44 63 118 70
19.. 1251-150 66 95 140 85
15.. 150.1—175 75 106 171 111
3.. 175.1-200 74 109 182 85
6... 200.1—225 100 133 213 154
4. . 2251-250 112 137 245 142
1 . . . . . . . . . 275. l—30O 73 142 296 65
4 . . . . . . . .. 300.1—325 114 150 311 100
3. . 3251-350 97 184 336 125
2 . . . . . . . . . 3751-400 81 125 385 122
1 . . . . . . . . . 4251-450 142 209 432 142
2 . . . . . . . . . 475.1-500 325 459 495 257
2.. 5001-525 192 308 521 401
1 . . . . . . . . . 6001-625 320 430 612 312
5.. 6501-675 310 445 682 533

Relation of Potash Removed by Crops to the Loss of Replaceable Potash
by the Soil

The estimation of replaceable potash and active potash Was made on
some of the soils after they had been cropped in the pot experiments.
The loss in replaceable potash caused by the cropping is the amount
before cropping less the amount after cropping. The potash removed
from the soils by the crops Was compared With the loss in replaceable
potash and with the loss in active potash. The results are given in
Table 5, arranged according to the potash removed by the crops.

Table 5.—Relation of Potash Lost from the Soil to the Loss of Active and of Replaceable Potash
in Parts Per lvlillion in the Soil.

Group It
According Loss of Replaceable Replaceable Replaceable
No. to Potash _ Potash Active Potash Potash Potash
Removed in Crops Potash Before fte_r Lost by
bv Crop by Cropping Cropping Cropping Cropping

11 0-50 42 1 6 120 100 20
20 51-100 79 24 132 102 30
31 101-200 145 42 201 140 61

1 201-300 238 35 184 130 54

1 401-500 460 68 521 244 277

3 501-600 527 309 661 350 31 1

4 601-700 639 171 564 343 221

1 701-800 735 140 771 380 391

 

The loss in replaceable potash and the loss in active potash are both

related to the potash removed. from the soil by the crops.

The loss in

POTASH REMOVED BY REAGENTS AND BY CROPS 13

replaceable potash averages a little more than the loss in active potash,
and is a little closer t0 the amount actually found. It is evident that
the crop does not feed entirely on the replaceable potash, or that the
replaceable potash as measured by the method here used does not take
out all the potash on which the plant can feed.

A statistical study of the 72 results give the correlation coefh-
cient between the potash removed by the crops and the loss in re-
placeable potash, r, to be —|— .797 i- .029. A previous study of the
potash removed by cropping and the loss in active potash on 408 samples
gave r as 7-]- .722 i .016. When the same group of 72 soils was used
for the calculation, the correlation coefficient for the active potash was
found to be + .780 —*_- .031 or practically the same as for the replaceable

potash.

Discussion of Results for Replaceable Potash

The close relation between the replaceable potash in the soil and the
potash removed by crops, and the fact that the replaceable potash in the
soil is not merely lowered by cropping, but the extent of the decrease is
related to the amount of potash removed by the crops, afiord excellent
evidence that the replaceable potash is used by the crops to a greater
extent than the other potash, and that the replaceabl potash is a measure
of the strength of the soil as regards potash. The same considerations
apply to active potash, but the amount of potash removediby cropping
is reflected to a somewhat greater extent by the replaceable potash than
by the active potash. The active potash and the replaceable potash no
doubt for the most part came from the same forms of combination in
the soil, though the replaceable potash is somewhat larger in quantity.

The laboratory manipulation of the estimation of active potash is
somewhat simpler and less difficult than that for replaceable potash, and
for this reason it is better adapted to routine work relative to the fer-
tility of different soils.

RELATION OF THE LOSS IN EXTRACTION OF ACTIVE POTASH TO
THE LOSS IN CROPPING

As previously pointed out, when a soil is cropped, there is a loss of
active potash, but the loss is less than the amount of potash removed.
Likewise when the extraction of active potash by 0.2 N nitric acid is
followed by a second extraction, an additional quantity of potash is
secured, equal to about one-fourth to one-half of the active potash se-
cured by the first extraction. Additional extractions will give up
further quantities of potash, although the amount will decrease, usually
gradually but sometimes quite abruptly.

The ability of a soil to maintain its supply of active potash, both to
cropping and to acid solvents, must be of significance both to soil fer-
tility and to soil chemistry. It may be asked whether the active potash
remaining after one cropping or more is as readily taken up as that

  
 

14-. BULLETIN NO. 391, TEXASiAGRICULTURAL EXPERIMENT STATION

originally present; whether additional amounts of potash become avail-T
able during the crop year; to what extent differences in active potash, if v
any, due to cropping, already exist in soils under investigation. Similar j
questions arise as to the relations of the active potash removed by suc- a
cessive extractions; what is the relative values of the potash to plants as 5
represented by the successive extracts; what is the relation of the 5
amount in the successive extracts to the fertility of the soil as regards f
potash; What is the relation of the potash lost by extraction to the loss ~.
by cropping. These are some of the questions which arise. .

The first extraction with 0.2 Nnitric acid does not remove all the 
potash soluble in this solvent. Successive extractions will give addi-
tional quantities of potash, the amounts depending upon the nature of 
the soil. The potash in the second extract may average one-half that ':
of the first extract in soils low in active potash. The proportion de- ;
creases as the active potash in the soil becomes larger until the second i,
extract may average one-fourth or less of the first extract in soils high
in active potash. 

The difference between the first and second extraction with 0.2 N 
nitric acid is here termed the loss in extraction, as a matter of con- 
venience. The loss in extraction is, of course, less than the active potash
secured by the first extraction.

Relation of the Loss in Extraction to the Potash in Crops

Table 6 contains the data averaged according to the loss of potash in
extraction as defined above. The loss of active potash in extraction of '
the soil with acid is closely related to the active potash lost from the
soil by cropping. The relations are indeed remarkably close, consider-
ing the fact that one is a chemical process and the other a process of
assimilation by the plant, in which the amount removed depends upon
the plant and other conditions. The loss in extraction is also related
to the active potash, the active potash increasing almost regularly with
the loss of potash in extraction. '

The potash in the second extract of the soil is related to the active
potash remaining in the soil after cropping, as is shown in Table 7. The
active potash left after cropping in the soils low in active potash is
larger than the potash in the second extract, which indicates a possi-
bility that some other potash is converted into active forms during the
cropping. This would indicate that some of the insoluble potash has
been rendered soluble during the growth of the crop. When a soil is
cropped, there is’ a loss of active potash. When a soil is extracted with
0.2 N nitric acid, there is a loss of soluble potash. In neither case is
the soluble potash completely exhausted.

POTASH REMOVED BY REAGENTS AND BY CROPS 15

Table 6.——Relation of Loss in Extraction of Active Potash to Loss 0f Active Potash by Cropping
- in Parts Per lVlillion.

Group by Loss Active Loss Active _
Number Averaged Loss i_n Potash_in Potash in Active
Extraction Extraction Cropping Potash
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-25 0 11 106

13 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25.1—50 36 36 78

15 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50.1—75 63 34 85

18 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75.1-100 91 72 135

16 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 100.1-125 111 78 161

23 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125.1—150 140 112 185

12 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150.1-175 164 165 277

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 1-200 186 166 273

1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 1-225 212 85 273

7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 1-250 229 270 371

3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 250 1-275 263 251 376

3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 1-300 296 208 456

2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 1-325 303 194 400

1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325 1-350 333 168 441

1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375 1-400 379 232 434

1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 1-525 521 432 628

2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 575 1-600 594 575 832

1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7251-750 742 708 1045

1 . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . 1025 . 1-1050 1048 593 1409

1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1050.1-1075 1051 683 1409

Table 7.—Relation of the Potash in the Second Extract from the Soil to the Active Potash
in the Soil After Cropping, in Parts Per Million.

Potash in Active Potash
Number Averaged Averaged Second After
by Groups Extract Cropping
27 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-25 19 46

43 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 1-50 37 67

19 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 1-75 61 89

7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 1—100 89 150

3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 1-125 117 205

6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125 1-150 134 164

2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 150 1-175 155 60

8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 175 1-200 194 111

6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 225 1-250 237 162

2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 1-300 287 100

2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 300 1-325 313 387

2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400 1-425 407 771

EFFECT OF THE NEUTRALIZATION OF THE BASICITY ON THE
ACTIVE POTASH AND RELATION TO CROPPING

One procedure for the estimation of active potash is to extract the
soil directly with 0.2 N nitric acid; another is first to estimate the
amount of 0.2 N nitric acid neutralized by the lime and magnesia in
other bases of the soil, and then to use sufficient acid to make the solu-
tion 0.2 N after the extraction. Each method has its advocates.

For the purpose of this study, the soils were divided into two groups.
One group includes those soils which neutralize less than 85 per cent
of the acid; the other group, those Which neutralize 85 per cent or more
of the acid. The active potash had already been determined in these
soils, without correction of the acid for neutralization. For thepurpose
of the Work, a preliminary digestion was made with acid; sufficient acid

16 BULLETIN NO. 391, TEXAS AGRICULTURAL EXPERIMENT STATION

was used to insure 0.2 N nitric acid after digestion 3 and a test was made
of the strength of the acid after the digestion t0 see that such was the

case. The remainder of the Work was similar t0 that already described. 

Results of the Work

The results secured Were studied in the following Way:

removed when the acid Was corrected for the bases removed. From these

figures were subtracted the amounts of potash actually removed by the l
The difference shows the extent to 1
The average J

average of the two crops grown.
which the actual results differ from the calculated results.
results are summarized in Table 8.

Table 8.—Potash Removed by One Crop Compared with That Calculated for Active With A

and Without Correction for Acid Consumed.

Number of Soils Total Amount of Net
Difference Differ- Average ,
ence Differ-

Acid Consumed - Per Soil ence

less than 85% + — Total + —~ Total
Active potash

not corrected. 30 24 54 739 754 ——l4 ——0.3 29
Active potash

corrected for

acid consumed 44 10 54 1885 305 +1580 29 40
Acid Consumed

more than 85%

Active potash

not corrected. 3 14 17 86 911 ——825 ——49 57
Active potash

corrected for

acid consumer’ 13 3 17 717 74 +643 +38 40

For soils neutralizing 85 per cent or less of the acid, the amounts of
potash to be removed by the crops calculated from the active potash
(without correction for acid neutralized) average very close to the actual
results secured; the net difference per soil is —0.3, While the average
difference, plus and minus, is 29 parts per million.
corrected for acid consumed, the results of the interpretation averaged» 29
parts per million higher than the actual; the average difference, plus
and minus, Was 40.

sumed is not made. The analysis is also a little shorter when the cor-
rection for acid consumed is not made.

The results are somewhat different when soils are used Which con-
sume 85 per cent or more of the acid. With 1'7 of these soils, both the
average difference and the net difference between the calculated amounts
of potash removed and t-he actual amounts removed, are slightly in
favor of making the corrections.

The potash 
Whichshould be removed from the soil by one crop was calculated from r
Table 3 in Bulletin 355, both for the active potash and for the potash ;

When the soil was at

Thus, the calculated results are more closely in ?
accordance with the actual results when the correction for acid con- 

The calculated value runs lower than‘

 

 

‘ ssrxsvurgr... " - -

POTASH REMOVED BY REAGENTS AND BY CROPS 17

the actual potash removed, when based upon the active potash not cor-
rected for neutralization, than when the potash corrected for acid con-
sumed is used. With both methods, however, the average difference and
the net difference are greater than for soils lOW in bases.

It does not seem that the degree of accuracy is improved by making
the correction for acid consumed. It would probably be better not to
make correction for acid consumed during the analysis, but to consider
the characteristics of soils high in lime in making the interpretation of
the results. The interpretation of analysis of such soils is more difficult
than that of less basic soils, as they are usually high in active potash,
and most of the potash taken up by plants is aifected by other factors
than the quantity presented by the soil.

SUMMARY OF CORRELATION COEFFICIENTS

The correlation coefficients Were calculated from the original data
and not from the averages given in the tables. The following is a sum-
mary of the correlation coefficients secured:

Water-soluble potash and potash in 2 crops: -|— .70 i .02.

Water-soluble potash and active potash: —|— .79 i .02.

Potash soluble in 12 per cent hydrochloric acid and potash in two
crops: -|- .72 i .02.

Potash soluble in 12 per cent hydrochloric acid and active potash:
—|— .72 i .02.

Replaceable potash and potash in two crops: + .91 i .01.

Replaceable potash and active potash: —|— .88 i .02.

Active potash and potash in 2 crops, the same soils used for replaceable
potash: + .89 i .02. A
p Replaceable potash lost from the soil in cropping and potash in the
icrop grown: 1+ .80 i .03. i
j Active potash lost from the soil in cropping, the same soils used for
replaceable potash, and potash in the crops grown: 1+ .78 i .03.

nvyfqzflavyrqvwrw Qwrfvw

SUMMARY AND CONCLUSIONS

g The Water-soluble potash in the soil, the potash soluble in 12 per cent
hydrochloric acid, and the replaceable potash in the soil are all related
zto the potash removed by crops in pot experiments and to the active
potash of the soils.

7 The water-soluble potash lost from the soil by cropping and the re-
laceable potash lost by cropping are related to the amount of potash
ken up by the crop grown on the soils and to the active potash lost
y cropping. '

if The amount of potash taken up by two crops usually averages 5 to 6
'_-n the water-soluble potash in the soil and about one-half the re-
I ceable potash in the soil.

 The amount of potash removed by the crops from the soil is usually
A to 16 times the water-soluble potash lost in cropping and about twice

    
   
   
  

18 BULLETIN NO. 391, TEXAS AGRICULTURAL EXPERIMENT STATION

the replaceable potash lost in cropping. The loss of replaceable pota‘
in cropping is greater than the loss of active potash by cropping. 

The difierence in the amounts of potash removed by a first and secon
‘extraction of soils with 0.2 nitric acid becomes greater as the potas
taken up by the crops in the pot experiments increase. _f

When a soil neutralizes 85 per cent or less of the acid used, the inter
pretations of the results are more closely in accordance with the resul
~of the pot experiments when the correction is not made for the neutrali 1_
zation of the acid, than when it is made. 

When the soils neutralize more than 85 per cent of the acid, the in;
terpretation of the results varies from the actual results a little 
when correction is made for acid consumed than when it is not, but n;
both cases the deviation is more than for less basic soils. It appea :4
better not to correct for neutralization but to take the highly calcareo 
nature of the soil into consideration in making the interpretation of the,
results. -