UNIVERSITY OF CALIFORNIA PUBLICATIONS
IN
AGRICULTURAL SCIENCES
Vol. 3, No. 10, pp. 271-282 June 22, 1918
DOES CaCOa OR CaSO* TREATMENT AFFECT
THE SOLUBILITY OF THE SOIL'S
CONSTITUENTS?
BY
C. B. LIPMAN and W. F. GERICKE
In 1850, Thompson1 showed that when soil is shaken with a solution
of sulphate of ammonia, calcium sulphate is brought into the solu-
tion. Using this observation as a basis, Way2 proceeded, in a classical
investigation, to study the nature of the phenomenon. He found that
when the calcium sulphate goes into solution as observed by Thompson,
there is an amount of base in the form of calcium and of other bases
set free in the solution equivalent to the amount of ammonium base
which is absorbed by the soil. From this fact and his observation that
clay carries the constituent which thus reacts with the sulphate of
ammonia, Way argued that there exist in the clay certain "double
silicates" of the alkalies and alkali earths with aluminum, which are
the active bodies in the reaction under consideration. He never proved
that such double silicates actually exist in the "clay" of the soil, but
believed them to be present there because his artificially prepared
double silicates of calcium and aluminum, of sodium and aluminum,
and others, behaved toward salt solutions like the clay, and lost their
absorptive and reactive powers, like clay, on ignition. In contra-
distinction to Liebig's view that the precipitation by soils of salts from
solution constitutes merely a physical phenomenon, Way believed that
the Thompson experiment, which typifies such soil-salt phenomena,
represents, really, a chemical reaction. Way's view became generally
i Thompson, H. S., On the absorbent power of soils, Jour. Roy. Agr. Soc, vol.
11, p. 68, 1850.
2 Way, J. T., On the power of soils to absorb manure, ibid., vol. 11, p. 313,
1850, and vol. 13, p. 123, 1852.
272 University of California Publications in Agricultural Sciences [Vol. 3
accepted and has been taught and is still very largely taught in the
agricultural colleges today under the subject of "fixation" or "ex-
change" of bases in soils. The presence in the soil of double silicates
or zeolites was thus assumed by soil investigators, and Hilgard gave
the idea much prominence in connection with his methods and
hypotheses on soil analysis. Further, the idea served as a basis for
the use, by Lawes and Gilbert, of sodium sulphate and of magnesium
sulphate in connection with the application of fertilizers to their
experimental plots with the end in view of setting free potassium, from
its silicate combinations in the soil, for use by the plant.
All of this has led to the statement, universally employed by authors
of texts on soils, that the application of lime and gypsum to soils
results, among other changes wrought by them, in the making "avail-
able" of potassium and other ions* of a similar nature. As recently
as 1907, Hall and Gimingham3 adduced experimental evidence on the
interaction between clay and ammonium sulphate, which appeared to
mark that reaction as one obeying the mass law, thus seemingly lend-
ing support to the validity of Way's hypothesis. Hall and Giming-
ham's evidence was soon shown by Cameron and Patten4 to be in-
complete, however. They demonstrated that the mass law does not hold
when a wider range of concentrations than that employed by the former
investigators is tested and a new Ivypothesis was necessary to explain
it. This was furnished by Van Bemmelen, who proved that absorption
by soils was closely parallel to that by colloids which he had studied,
and which may be explained by the formula y/m<=Kc1/n in which
y is the amount absorbed by a quantity m of the absorbent, c the con-
centration of dissolved substance when equilibrium is attained, and
K and n are constants depending on the nature of the solution and the
adsorbent. Such a formula has since been shown to hold for absorp-
tion of phosphates by Prescott5 and for absorption of ammonium salts
by Wiegner.6 In accordance with this conception of the soil as a
colloid-containing body, the colloidal particles possess the power of
holding ions which are adsorbed from salt solutions and give such ions
up with relative facility to new solutions containing other ions for
which they are substituted.
* In this case, and throughout this paper, the term "ion" is not used in the literal sense
It is not intended to convey the idea that the authors believe that a given ioi by itself is
absorbed or set free, for we are actually inclined to the belief that in these cases, as in absolu-
tion by plants, not ions, but compounds, are absorbed as units.
•"• ITall, A. D., and Gimingham, C. T., The interaction of ammonium salts and
the constituents of the soil, Trans. Chem. Soc, vol. 91, p. 677, 1907.
4 Cameron, F. K., and Patten, II. E., The distribution of solute between water
and soil, .lour. I'hys. Chem., vol. 11, j). 581, 1907.
19] 8] Lipman-GericJce : CaCOs and CaS04 and Soil Solution 273
This idea has, however, been confused with the zeolitic hypothesis
from which, in some respects, it is quite distinct. Due to both concepts,
the teaching is still largely in vogue that CaC03 and CaS04 possess
as one function in soils a power to set potash and other bases free from
their insoluble combinations. In spite of the general acceptance of
this view, however, some practical agronomists have called it in ques-
tion and it seems necessary to determine if the hypothesis and the
laboratory experiments used in support thereof are valid. Briggs and
Breazeale7 have recently made an attempt to answer definitely the
question as to whether or not lime or gypsum applied to soils does
affect the potassium content of the soil solution produced by ortho-
clase, pegmatite, or orthoclase-bearing soils in contact with water.
They checked their results b}^ growing young wheat seedlings in the
solutions produced by the treatment of the mineral or soil with lime
or gypsum and water. As a result of these experiments, they con-
clude that the "availability to plants of the potash in soils derived
from orthoclase-bearing rocks is not increased by the addition of lime
or gypsum. In some instances, a marked depression of the solubility
of the potash in the presence of gypsum was observed." While the
authors specifically refer to "soils derived from orthoclase-bearing
rocks," the statement carries the implication, owing to the stated
object of their investigation, that the potash-bearing silicates of any
kind in soil are not likely to be affected in solubility by the addition
to the soil of lime or of gypsum. The fact that this conception is con-
trary to what one would expect from theoretical considerations regard-
ing soil-solution reactions, appeared to render it desirable to investigate
the subject farther. We therefore planned and executed the following
experiment :
Calcium carbonate or calcium sulphate were each added to soils, and
throughly mixed with them in the different cases as further indicated
in the tables. The soils thus mixed were placed in pots in the green-
house. Water was added to make optimum moisture conditions and
such moisture conditions were maintained for a period of nine months.
Three soils were used, viz : Oakley blow sand, Berkeley clay adobe, and
a greenhouse soil, the latter having been originally made by admixing
s Prescott, J. A., The reaction between dilute acid solvents and soil phos-
phates, Proc. Chem. Soc, vol. 30, p. 137, 1914.
s Wiegner, Georg., Zum Basenaustausch in der Ackererde, Jour. Landw., vol.
60, pp. 110 and 197, 1912.
7 Briggs, L. J., and Breazeale, J. F., Availability of potash in certain ortho-
clase-bearing soils as affected by lime and gypsum, Jour. Agr. Ees., vol. 8, p. 21,
1917.
274 University of California Publications in Agricultural Sciences [Vol. 3
barnyard manure with the Berkeley clay adobe soil. The applications
of CaC03 and of CaS04 were made on March 9, 1917, and in the
manner and quantities indicated in the tables. Control soils, untreated
with either lime or gypsum, were, of course, included in the experi-
ment, but were otherwise treated like the other soils. The soils in
all pots were sampled three times, at considerable intervals, as shown
in the tables. The samples were taken so as to represent the whole
depth of the soil layer in the pot and of different parts thereof. Eight
hundred gram portions of these samples, in air-dry condition, were
mixed with 1600 cc. of distilled water in large bottles and allowed to
digest for six days with occasional shaking during every day. After
six days, the solutions were filtered through Pasteur-Chamberland
pressure filters and analyzed by gravimetric or volumetric methods
for the constituents named in the tables. Large enough aliquots could
be employed, owing to the method which we have devised and described
above for mixing the soil and water, to insure accurate results by the
standard methods of analysis intended for larger quantities of the
same substances. We employed no checking system by means of
germinating plants, such as that used by Briggs, because (1) we do
not believe that a few days' growth of plants constitutes any reliable
criterion regarding any factor in plant growth, and (2) the evidence
obtained by Burd, Hoagland, and Stewart has demonstrated that for
plants grown to maturity, an intimate relation holds between the
nature of the soil solution and absorption of nutrients by plants grow-
ing in such soil solutions in every stage of growth. In other words,
we contented ourselves with trying to determine whether or not the
soil solution is enriched with respect to potassium and other elements
by the treatment of soil with CaC03 or with CaS04 as indicated by
the composition of the soil extracts obtained by us. The results of the
analyses of the soil extracts are shown in the subjoined tables, in which
the amount of every ion sought and found in the solution is expressed
in parts per million of the soil.
For the sake of greater simplicity and brevity, we shall at first
discuss the tables separately.
Tn table 1, we see the results obtained with the Oakley soil, from
which it is clear that both lime and gypsum are without effect on the
amount of water soluble potassium in that soil. The latter behaves in
this respect like the Oatman soil from Riverside County in this state,
which Brings and Breazeale have studied. There is little reason to
believe, likewise, from the data under consideration that the water
1918]
Lipman-Gerlcle: CaCO-> and CaS04 and Soil Solution
Table 1. Oakley Soil
Treatment :
Date
Fe
Ca
Mg
S
K
P
Rate per acre
kilograms
of
samplin
g
In parts per mill
ion of dry
soil
Control
Apr. 9,
'17
1.0
16
2.3
17
9.1
500 CaCC-3
Apr. 9,
'17
3.6
23
3.9
16
8.1
1000CaCO3
Apr. 9,
'17
3.4
31
6.9
21
10.3
500 CaS04
Apr. 9,
'17
1.4
32
3.1
21
9.7
1000CaSO4
Apr. 9,
'17
1.4
63
1.0
20
10.7
Control
July 20,
'17
1.2
13
3.6
10
7.9
6.9
500 CaCC-3
July 20,
'17
2.0
27
6.7
10
7.8
5.8
1000 CaCOs
July 20,
'17
1.4
26
9.3
10
8.4
10.4
500 CaS04
July 20,
'17
1.4
26
1.6
23
8.3
5.5
1000CaSO4
July 20,
'17
1.4
62
0.9
45
6.9
8.1
Control
Dec. 24,
'17
1.4
24
1.3
19
8.8
6.7
500 CaCC-3
Dec. 14,
'17
1.4
31
1.3
14
9.1
7.2
1000 CaC03
Dec. 24,
'17
1.5
34
1.3
13
9.9
6.1
500 CaSo4
Dec. 24,
'17
1.0
44
1.7
30
7.3
6.7
1000CaSO4
Dec. 24,
'17
0.6
61
1.3
64
8.0
6.3
Table 2.
Adobe Soil
Treatment :
Date
Fe
Ca
Mg
S
K
P
Rate per acre
kilograms
of
samplinj
In parts
5 per milli
ion of dry
soil
Control
Apr. 23,
'17
0.7
17
0.7
7.4
1000 CaC03
Apr. 23,
'17
0.7
25
1.4
12.8
1000 CaS04
Apr. 23,
'17
0.8
50
1.1
9.6
Control
July 20,
'17
0.7
32
2.1
32
9.7
7.2
1000CaCO3
July 20,
'17
0.7
34
4.2
31
15.0
7.8
1000CaSO4
July 20,
'17
0.7
78
2.1
124
12.4
7.5
Control
Jan. 2,
'18
1.6
47
2.6
32
8.3
5.6
lOOOCaCCv,
Jan. 2,
'18
1.6
46
2.6
31
8.8
6.1
1000 CaS04
Jan. 2,
'18
1.0
84
146
10.0
5.7
Table
3. Greenhouse
Soil
Treatment :
Date
Fe
Ca
Mg
s
K
P
Rate per acre
kilograms
of
sampling
In parts
; per milli
on of dry
soil
Control
Apr. 20,
'17
7.8
83
9.3
40
14.4
500 CaC03
Apr. 20,
'17
15.5
112
19.5
42
15.3
lOOOCaCC-3
Apr. 20,
'17
8.3
115
25.5
49
25.4
500 CaSo4
Apr. 20,
'17
7.0
157
17.8
91
20.4
1000 CaS04
Apr. 20,
'17
7.8
210
6.7
106
27.0
Control
July 20,
'17
4.5
86
8.6
51
23.8
14.0
500 CaC03
July 20,
'17
7.8
91
20.6
86
25.0
12.3
1000CaCO3
July 20,
'17
5.6
104
24.3
82
38.6
12.3
500 CaS04
July 20,
'17
4.5
129
9.3
130
28.2
11.4
1000CaSO4
July 20,
'17
4.2
162
5.2
165
34.8
10.1
Control
Jan. 12,
'18
11.9
93
3.9
55
12.8
20.2
500 CaC03
Jan. 12,
'18
9.8
128
5.0
76
15.4
19.6
1 000 CaC03
Jan. 12,
'18
9.8
142
5.4
76
32.0
18.4
500 CaS04
Jan. 12,
'18
9.7
176
4.0
182
17.7
16.7
1000 CaS04
Jan. 12,
'18
9.8
171
4.3
219
22.4
17.1
276 University of California Publications in Agricultural Sciences [Vol. 3
soluble phosphorus and the water soluble sulphur in that soil have been
affected by CaC03 and the first by CaS04. The calcium content of
the solution is affected by both CaC03 and CaS04, as would be ex-
pected, but which does not necessarily have to occur. On the other
hand, the water soluble iron content of the soil appears possibly to
be slightly affected by the CaC03 treatment, at least in the first
sampling; and the magnesium content of the water extract shows, it
seems to us, very distinct accretions, through the CaC03 applications,
in the first and second samplings. The effect seems to have dis-
appeared, however, by the time the third sampling was made and a
new equilibrium is probably established. On the contrary, gypsum
seems to depress the amount of water soluble magnesium in the soil
solution of the Oakley soil. This appears to be definitely true by the
time the period of the second sampling has been reached, and less
definitely in the period of the first sampling with the larger gypsum
application. Just as the tendency to increase in amount in the soil
solution through the instrumentality of the treatment seems to char-
acterize both the ions, magnesium and iron, in the periods up to and
including the second sampling, a reverse tendency is manifested by
these ions by the time of the third sampling. In the soils treated with
CaC03, there is a definite decrease in magnesium, in the solution, in
the period named and the iron content of the same soil solutions seems
to decrease simultaneously. Yet the other ions do not seem to have
been affected in that way in the same period, but have either remained
stationary or have shown increases. These rather marked changes
evidenced by the figures of the second and third samplings are even
more distinct in the cases of the other soils, to which reference will be
made below.
In the Berkeley clay adobe soil, the data for which are given in
table 2, conditions are quite evidently not the same as in the Oakley
soil. While the potassium content of the latter soil's solution remained
unaffected by the application of either CaC03 or CaS04, that of the
former soil seems to us to be definitely increased by both CaC03 and
CaS04 in the first two samplings and by CaS04 alone in the last
sampling. The greater effect in that direction is clearly induced, how-
ever, by CaC03. The iron content of the soil solution in the clay
adobe soil remains entirely unaffected by the treatment which is
accorded the soil. The phosphorus content of the soil solution affected
by CaCOa may, perhaps, be slightly increased in both the second and
third samplings, but the data do not give us leave to be certain on
1918] Lipman-GericJce : CaCO-^ and CaSO± and Soil Solution 277
that point. The calcium and sulphur content of the soil solution behave
as one would expect without experiment in the clay adobe soil treated
with CaS04, but the calcium content of the same soil treated with
CaCOg is affected to a small degree in some cases and not at all in
others. The magnesium content of the clay adobe soil solution behaves
similarly to that of the Oakley soil solution, but the increases due to
CaC03 treatment of the soil are not as large in the former as in the
latter. Again CaS04 seems to be without effect in that direction. In
general, the behavior of the clay adobe soil solution, as judged by our
analyses, parallels that of the Oakley soil solution in the third samp-
ling, a condition of equilibrium, and, in general of a more dilute
solution, having been attained. That does not hold, however, for the
soil treated wTith CaS04. In general, therefore, the results obtained by
us with the clay adobe soil, among other things, show a lack of agree-
ment between our results and those of Briggs and Breazeale regarding
the effect of CaC03 and CaS04 on the potassium content of the soil
solutions in question.
Coming finally to a consideration of the greenhouse soil, we find in
table 3 some very interesting data, and the most definite of any sub-
mitted in all the tables, inasmuch as the changes due to soil treatment
are so much larger than those characterizing the other soils. Con-
sidering the data for potassium first, we find that marked increases in
the amount of that ion in the solution of the greenhouse soil are
induced by the larger application of CaC03 and by both the smaller
and larger applications of CaS04. Moreover, even the smaller appli-
cation of CaCO?> seems to induce the solution of definitely larger
amounts of potassium than those found in the solution of the untreated
greenhouse soil. In the periods of the first two samplings, the iron
content of the soil extract seems to have been increased by the CaC03
applications, but not by the CaS04 applications. Moreover, the smaller
CaCOg application seems to have been much more effective in that
direction than the larger application. By the time of the third
sampling, the effects just mentioned appear to have vanished, and in
fact, it is possible that they have been supplanted by a depression in
the amount of iron in the soil extract. The general direction taken
by the effects of the soil treatment on the calcium content of the soil
extract is wrhat one would expect a priori. The results indicate, how-
ever, the inaccuracy of the method of determination considered, in the
large, since the relations between the CaC03 and CaS04 applications
in small and large amounts do not maintain themselves constant.
278 University of California Publications in Agricultural Sciences [Vol. 3
This holds, of course, for the other soils as well as for the greenhouse
soil, indeed, more markedly so. The phosphorus content of the soil
extract is certainly not increased, in the two determinations made, by
the treatment of the soil under consideration. In fact, while it is
difficult to appraise it as such, there seems to be a slight depression
in the amount of the phosphorus present in the soil extracts of the
treated, as against those of the untreated soils. The magnesium is
affected in the greenhouse soil similarly to the manner in which it
was influenced in the other soils, but, as in the case of the potassium,
the results are much more emphatic. It is quite evident that large
amounts of magnesium go into solution through the influence on the
soil of CaC03 throughout the period of the experiment, but especially
in the periods of the first two samplings. CaS04, on the other hand,
only increases the amount of magnesium when employed at the smaller
application and then only in the period of the first sampling. With
the larger application of CaS04, in the first sampling and with both
applications in the second sampling, there seems to be evidence of a
depression in the magnesium content of the soil extract. In the third
sampling, the CaS04 treated soils seem to behave like the control and
furnish another instance of the phenomenon noted above in the case
of the other soils. The sulphur content of the soil extract is more
markedly affected by the treatment in question in the case of the green-
house soil than any other constituent thereof which we have deter-
mined. That is, perhaps, not surprisingly so in the case of the CaS04
treatment, but it is to be particularly remarked how very great such
increases are even with the CaC03 treatment. Unlike the cases of the
other constituents of the soil extract, moreover, that of the sulphur
shows the effect of treatment even at the third sampling.
General Discussion
From a general survey of our results, a few facts stand out clearly.
Of the seven ions which we have determined in the extracts of the
soils treated with CaC03 or with CaS04, all, with possibly one excep-
tion— phosphorus — are affected by the treatment in one or more of the
three soils, in the directions either of increase or decrease in amount
in the soil solution. The ions are not all affected by the treatment in
any one soil, however. It appears that the nature of the soil minerals.
jis well as the organic matter content of the soil, and hence probably
the partial carbon dioxide pressures, are important factors in deter-
1918] Lipman-GericJce : CaCO:> and CaS04 and Soil Solution 279
mining how CaC03 or CaS04 will affect the soil reactions and the
precipitation or the greater solution of given ions in any soil. This
marked disparity between the nature of soil reactions and their results
in different soils, seems to have been but slightly appreciated, if at all.
among soil investigators. We therefore find, on the one hand, the
iterated and reiterated statements in our text-books respecting the
effect that lime or gypsum, or both, exert on the available potash
supply in the soil solution; and, on the other hand, such statements
as that by Briggs and Breazeale to which we have made reference
above, which deny directly or inferentially the effectiveness of lime
and gypsum, in that direction, for a certain soil or a certain mineral ;
and through the absence of comparison with other soils imply the
denial of the existence of such effects in general. As is freqently the
case in all matters, the truth lies between these extreme views. Potas-
sium from the soil minerals is rendered soluble in greater quantity
than normally by applications to the soil of both CaC03 and CaS04
in some soils, but not in others. Of the three soils which we have
studied, two seem to us to show clearly the former and one the latter
effect.
"Working also with only one soil (Dunkirk clay loam), Lyon and
Bizzell,8 by the indirect method of studying drainage water from
lysimeters, and by the possibly direct method of studying absorption
by plants, showed, prior to the work of Briggs and Breazeale, that
liming of soils does not increase the potassium content of the drainage
water, or of plant substance. But, it should be noted too, that in other
respects their results are also at variance with ours. For example,
they found that the application of lime to soil (to be sure it was CaO
and not CaC03) did not increase, and in general, actually depressed
the amount of calcium in the drainage water and hence probably,
though not necessarily, in the soil solution; whereas we have found
the calcium content to be higher and distinctly so in all soil extracts
but one from soils treated with either lime or gypsum regardless of the
soil 's nature. In our opinion, these apparent disagreements are really
only manifestations of the marked differences characterizing the
physical-chemical systems which we call soils in equilibrium with
water. When we consider soils as such systems, dynamic and not
static in nature, and in addition apply to them the Van Bemmelen
formula for absorption by colloids, it is not difficult to understand the
s Lyon, T. L., and Bizzell, J. A., Calcium, magnesium, potassium and sodium
in the drainage water and from limed and unlimed soils, Jour. Amer. Soc. Agron.,
vol. 8, p. 81, 1916.
280 University of California Publications in Agricultural Sciences [Vol. 3
discrepancies in the reactions between different soils and CaC03 or
CaS04, which we have been studying. While thus we are in apparent
disagreement with the principle of the indirect results of Lyon and
Bizzell regarding the effect of lime on the calcium content of the soil
solution, we are not actually so. On the other hand, we are in actual
agreement with them as regards the effect of calcium applications on
the magnesium content of the soil solution. In all soils studied by us.
we find increases of magnesium in the soil solution, due to CaCO.,
applications, but this does not imply that the same would hold for
all other soils. Again, we are in agreement with the indirect results
of Lyon and Bizzell regarding the sulphur content of the soil solution
as affected by lime applications in the case of the greenhouse soil, but
not in the case of the clay adobe soil, and probably not in the case
of the blow sand.
If we may repeat, therefore, we are apparently forced to conclude,
from the results of our experiments and from such comparisons of
them with those of others as we can make, that no general idea of the
effect of CaC03 or of CaS04 on the potassium content of any other ion
in the soil solution can be adduced from any one soil or from any one
general kind of soil. In some soils, large accretions of soluble potas-
sium to the solution may be obtained by CaC03 or by CaS04 applica-
tions ; in others no increases may be obtained. This may hold for any
ion, but does not preclude the probability that some ions may be
rendered soluble in larger amounts by CaC03 in any soil. Whether
or not the ions which are rendered soluble in greater amounts by the
application to the soil of CaC03 or CaS04, or both, are also available in
such larger amount to the plant roots is another question, an affirmative
answer to which does not necessarily follow from such an answer to the
question which we are discussing here. It is to be noted from our
results, also, that the time of the year at which ions are sought in the
soil solution, or at least the period elapsing between the application
of CaCO., or of CaS04 to the soil and the sampling of the latter, are
important factors in determining the results of one's findings and
cannot be overlooked in any such investigations.
In anticipation of queries which may arise from readers of the fore-
going discussion, we desire to make very clear and emphatic the follow-
ing general statement. We do not believe that all of the data given
by us in the tables are significant, because we appreciate the large
error which probably attaches to our method of obtaining the soil
extrad and of analyzing it. Our calculations are such, therefore, as
1918] Lipman-Gerichc: CaCOo and CaS04 and Soil Solution 281
not to be dependent, in any large degree, upon the significance of any
isolated portion of our data. The table which we hold to be most
significant is table 3 and the two chief conclusions which we desire to
draw from our work are (1), that a soil may be distinctly affected, as
regards the solubility of its constituents through its treatment with
CaC03 or with CaS04 ; and (2) , that this is not necessarily so, however,
and may hold for one soil and one constituent in one case, and not in
another, depending on the nature of the physical-chemical systems
dealt with and upon the composition of the soil mineral complexes. In
these two conclusions from our experiment, one can find a reconciliation
of the two diametrically opposed views with regard to the effects of
CaC03 and CaS04 on soils and we offer our discussion as a contribu-
tion to such a reconciliation.
Summary
From experiments to determine how CaC03 and CaS04 affect the
water soluble iron, calcium, magnesium, potassium, sulphur, and phos-
phorus in soils as determined by ordinary water extractions, the fol-
lowing outstanding conclusions were drawn :
1. All soils do not behave alike when treated with CaC03 or with
CaS04. They should not be expected to do so, considering th^ir
mineral composition, the law of chemical equilibrium, and the nature
of colloid action in soils. With this conception as a basis, the con-
flicting statements in our literature on the effect of CaC03 and CaS04
on the soluble potassium supply in soils may easily be accounted for
and each view may be regarded as correct under certain circumstances.
2. Potassium was found to be rendered more soluble by CaC03 and
by CaS04 applications in clay adobe soil and in a greenhouse soil made
therefrom, but not in a blow sand soil.
3. The soluble calcium content was increased in all soils studied
by CaC03 or CaS04 applications. This does not prove that the same
will hold true for all other soils.
4. The soluble magnesium content of all soils studied was increased
by CaC03 treatment. It seems to have remained unaffected or even
to have been depressed by CaS04 treatment in all but one case in each,
the Oakley and the greenhouse soil with the small gypsum application.
5. The soluble iron content was probably increased in the solution
of the greenhouse soil by the treatment in question. It seems also to
282
University of California Publications in Agricultural Sciences [Vol. 3
have been so increased for a time in the blow sand, but not in the
clay adobe soil.
6. The soluble sulphur content was increased in the solution of the
greenhouse soil by CaC03 applications and probably also in that of
the blow sand, due to similar treatment.
7. The phosphorus content of the solutions of the three soils studied
seems to have remained unaffected by the treatments accorded the
soils. The indications are, however, that a slight depression in the
amount of the water soluble phosphorus may have resulted from the
CaC03 or the CaS04 applications in one case. In this case also no
generalization is attempted.
8. It seems that our current teachings on soils and plant physiology
should be corrected with these results as a basis.
Transmitted June 4, 1918.
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