STUDIES OF SULFUR IN RELATION TO THE
SOIL SOLUTION

BY

WILBUE L. POWERS

CONTENTS

PAGE

Introduction 120

Scope of the experiments 124

Relation of replaceable bases and sulfofication to the soil solution 125

Chemical experiments 127

Sulfur and sulfates and the soil solution 127

Sulfur and soil solutions of different soils 130

Sulfur and alfalfa yield with soils in jars 133

Hydrogen ion concentration in cropped and fallow soil pots 134

Physiological experiments 135

Preliminary studies 135

Sulfur and chlorophyll 141

Water culture experiments with seedlings 141

How does sulfur go into the plants? 142

Calcium sulfate versus potassium sulfate 143

Complete nutrient solution versus displaced soil solution 146

When does alfalfa most need sulfur? 148

Crop-producing power of limited amounts of sulfur with alfalfa 150

Concentration of sulfate needed for optimum growth of alfalfa? 152

Sulfate concentration experiments with culture solutions 155

Inorganic sulfur 155

Yield and inorganic sulfate content as affected by sulfate concentration ... 157

Sulfate concentration experiment with solid culture medium 159

Reaction studies 160

Discussion 161

Is sulfate concentration in soil solutions sometimes too low for best growth? 161

Does sulfur serve to hold calcium and other bases in solution? 162

Will the average application of sulfur hasten soil deterioration? 164

Does sulfur improve reaction of arid soils for alfalfa? 164

Summary 165

120 University of California Publications in Agricultural Sciences [Vol. 5

INTRODUCTION

Sulfur has given excellent results as a fertilizer for the past twelve
years when applied to many of the nearly neutral, semi-arid, basaltic
soils of the northwestern United States, especially when used on
legumes. More than 120,000 acres in Oregon can be expected, with
sulfur, to yield an additional ton an acre of alfalfa a year. One-third
of this area has been sulfured.

The reason for the marked increase in yield is not well under-
stood, even though an extensive literature on the agrotechnic use of
sulfur has accumulated. Possible deficiency of sulfur in soils has
not been seriously considered until recently when better methods of
analyses revealed much larger quantities of sulfur in plant tissue than
was reported by earlier investigators.23 Assuming that the quantity
of sulfur in plant tissue is an indication of the amount required for
normal growth processes, it is readily seen why sulfur is given more
consideration than formerly in studies of crop production. The supply
of sulfur found in soils by modern methods of analysis51' 54 emphasizes
the relative importance of this element. Elemental sulfur has been
extensively studied during the past dozen years in relation to its effect
on soils, soil micro-organisms, and plants. The adequacy of the supply
of sulphate in the soil solution has been questioned and the study of
gains and losses in soil sulfur has been given much attention.

The supply of sulfur in soils is in many instances less than that
of phosphorous.50 The total sulfur content of normal soils can be
expected to range from 300 to 1200 pounds in two million.40' 51 Many
of the surface soils of the northwest contain less than 500 pounds of
sulfur in 2,000,000, and often run as low as 100 to 300 pounds in the
plowed surface of an acre in leached basaltic land. A six-ton alfalfa
crop may remove 30 pounds of sulfur an acre. Certain soils that
have been cropped for a generation appear to have lost 20 to 40 per
cent of the initial sulfur content. The sulfur content of soils seems
to vary with the organic matter supply and is usually largest in the
surface soil.

Analyses of percolate from lysimeters, where the amount drained
out annually is not large, may indicate the nature of the soil solution.53
The percolate from the Cornell lysimeters contains sulfur lost at the
rate of 30 to 4i pounds an acre each year;40 in Iowa,10 67 pounds;

1927] Powers: Studies of Sulfur in Relation to the Soil Solution 121

at Rothamsted,46 71.6 pounds; at Bromberg, Germany,19 about 100
pounds; and in Wisconsin23 and at Oregon Experiment Station the
loss in drainage has been 15 to 40 pounds an acre a year, or about
four times the amount received in precipitation.50

The concentration of sulfate ion in water extracts of soil has often
been 100 parts per million or more and often approximates half the
concentration of sulfate in the displaced soil solution. Burd9 reports
concentrations of sulfate in displaced solutions from California soils
of from 118 to 655 parts per million. Sulfate was found to increase
in fallow and to help hold cations in solution, especially when nitrates
were depleted by crops or reduced by anaerobic bacteria.

The soil solution is not diluted with sulfur-free rain water. Ames
and Boltz3 present data showing 9 pounds of sulfur per acre in the
country and 72 pounds in town received annually from rainfall.
Different investigators50 report determinations showing wide varia-
tions between amounts of sulfur thus gained or lost in different
sections of the country.

Sulfur is often added to land in barnyard manure, potassium
sulfate, ammonium sulfate, commercial "superphosphate," or as cal-
cium sulfate. Especially in southeastern United States, where much
commercial fertilizer is used, the practice tends to overcome any
possible crop depression from lack of a sufficient concentration of this
nutrient in the soil solution. Sulfur seems to be more abundant in
soils originating from granitic rock than in soils of basaltic origin.
Sulfates may accumulate with alkali, as in the Great Basin region,
owing to absence of drainage for its removal.

Hart and Peterson in 191123 announced new figures for the sulfur
content of crops, showing that Leguminosae and Cruciferae are
especially heavy users of sulfur. Reimer and Tartar51 found that a
six-ton crop of alfalfa removed about 30 pounds of sulfur an acre.
Recent data by Jones32 tends to reduce this amount slightly.

One well established function of sulfur is that of increasing the
protein content of alfalfa.51' 45 It is said to be present in the protein
cystine.47' 53 Evidence has been found that the SH group in cystine
plays a catalytic role in synthesis of vegetable fats in plant cells.44' 58
Increased root and nodule development22' 51 and a richer green color
have commonly resulted from use of sulfur on alfalfa. Stiffer straw
and heavier seed has been noted from sulfur or sulfate applications
to grain land15' 34 Harris et al24 reported a higher concentration of
sulfate in the leaf-tissue fluids of Upland than of Egyptian cotton

122 University of California Publications in Agricultural Sciences [Vol. 5

and suggest that this difference may be related to drought resistance,
alkali resistance, and the concentration of sulfate ions in the soil
solution.

Adequate evidence does not seem to have been found to establish
any close relation between the total sulfur in soils and the sulfate
content of the soil solution or sulfate requirement of crops. It seems
probable that plants may contain more sulfur than required perhaps
both in organic and inorganic form where the sulfate concentration
of the soil solution with which they are grown is high.

Numerous investigators have found50 that with heavy applications
of sulfur to soils there is an increase in concentration of free hydrogen
ions somewhat proportional to the amount of sulfur applied and
oxidized to sulfates. Adams1 demonstrated that sulfate formed may
be leached out, while the acidity is not removed. Hydrogen ion seems
to participate in an exchange for absorbed cations, such as calcium
ion, permitting the hydrogen ion to remain with the soil as an acid
silicate, while the calcium ion is leached out in association with sulfate.
The amount of increase in concentration of hydrogen ions in the soil
solution as a result of sulfur applications may depend on the amount
of readily soluble bases present and general buffer effects of the soil.

Lipman,30 Kelley,33 and others have suggested sulfur for correcting
the reaction of "black alkali" soil by increasing the hydrogen ion
concentration upon oxidation and combination with water. This acid
may then dissolve calcium compounds and bring about exchange of
such multivalent bases for sodium in the solid phase and thus improve
permeability and reaction of "black alkali" land. Johnson and
Powers30 found sulfur an effective chemical treatment for such land
under eastern Oregon conditions, especially when used in combination
with gypsum or manure. Sulfur may improve the reaction of an
alkaline soil, flocculate colloids so as to permit better drainage, and
tend to dissolve calcium from its compounds, all of which may improve
soil conditions for legume crops.

The Lipman37' 38 process of rendering rock phosphate soluble
depends upon the production of acid by oxidation of sulfur to produce
soluble phosphate. Lipman and his associates have studied the most
economical proportion of soil, sulfur, and "floats," best suited to
moisture and climatic conditions, for economical production of avail-
able phosphates. Good results have been secured in western Oregon
by applying rock phosphate in combination with sulfur and manure
alternated with lime.50 A reciprocal relation between phosphates and

1927] Powers: Studies of Sulfur in Relation to the Soil Solution 123

calcium in solution in the soil has been shown by Burd8 and by
Stephenson and Powers.50 A moderate increase in acidity may tend
to increase phosphate in the soil solution while higher acidity may
increase calcium ions and aluminum ions and precipitate phosphate
to a relatively insoluble form.

There has been some controversy as to whether calcium sulfate or
sulfur liberates potassium in the soil. According to Lipman and
Gericke33 this depends upon the particular soil. Different investi-
gators have reported the potassium content of soil water extracts
to be somewhat increased as a result of sulfur or sulfate applica-
tions.16' "- 46

Maclntire39 has pointed out a relation of sulfur applications to
increased loss of calcium in percolate from lysimeters. This relation
has been found to hold true with two Oregon soils employed in
lysimeters at Oregon Experiment Station. Adams1 held that it was
difficult to find much calcium in solution in acid soils with a hydrogen
ion concentration as great as pll 5.0. Stephenson and Powers56 found
that the most striking effect of sulfur on water extracts of three soils
tested was the increase in calcium ion in solution. This effect would
be expected to be less marked upon acid soils which have been rather
thoroughly leached of soluble calcium compounds.

Nitrification and sulfofication largely result from biological activi-
ties. A little sulfur may stimulate ammonifieation.49 Sulfur may
oxidize and unite with ammonia as sulfate of ammonia.2 McCool43
finds that sulfur aids decomposition of organic matter and formation
of nitrates. A little sulfur appears to aid nodule development49' S1
and nitrification45, 46 in arid soils, while larger applications may result
in increasing the hydrogen ion concentration sufficiently to depress
nitrogen fixation and nitrification. Rudolfs54 observed five times
more bacteria in alkaline soil that was neutralized by sulfur. Burd
and Martin11 have noted a reciprocal relation between the amount of
nitrates and sulfates obtained in the soil solution. Whenever sulfur
stimulates growth of legumes an increase may be expected in nitrogen
supply in the soil and of nitrate in the soil solution.

Recent investigations lead to the conclusion that the supply of
available sulfur, like the supply of available nitrogen, follows a fairly
definite cycle. Joffe29 concludes that making acid phosphate by the
Lipman process is chiefly a problem of providing favorable conditions
for sulfur oxidation. Brown and Kellogg7 find that soils have a fairly
definite sulfur oxidizing power.6 Lipman and McLean38 report that

124 University of California Publications in Agricultural Sciences [Vol.5

temperature, aeration, moisture content, and proportion of materials
affect sulfur oxidation, and they find no advantage in starting sulfur
oxidation with a soil of high acidity. Halversen and Bollen21 report
that sulfur application increases the sulfur oxidizing power of soils;
they find little need for inoculated sulfur for many Oregon soils. It
appears that heavy textured soil is unfavorable and good organic
supply is favorable to rapid sulfur oxidation in soils. Brown and
Gwinn5 note that phosphorus and manure increase sulfofication in
loam soils. Stephenson59 has recently demonstrated that the rate of
sulfur oxidation is related to the surface area and that sulfur, ground
to pass a forty-mesh sieve, should oxidize at a rate adequate to meet
plant needs. Boullanger and Dugardin4 suggest that certain sulfur
compounds are oxidation catalysts. The possibility that sulfur oxida-
tion increases anion concentration, thus holding cations in the soil
solution and bringing about conditions favorable to base exchange
reactions, will be developed later.

A review of the laterature emphasizes the need of further investi-
gation as to the role of sulfur in the soil solution.

The writer wishes to acknowledge his indebtedness to Dr. W. F.
Gericke for helpful counsel during the course of these investigations.

SCOPE OF THE EXPERIMENTS

The primary purpose of experiments reported herein has been
to determine the effects of sulfur on soil solutions and their relation
to sustained crop production. The study has included the effects of
sulfur on soil reaction, liberation of bases, and concentration of sulfate
and other anions, especially as related to the nutritive requirements
of alfalfa at different growth periods and to sustained productiveness
of soils.

The main study has been chemical, supported by some physio-
logical experiments and confirming field trials, and has included four
lines of attack, as follows : ( 1 ) effect of sulfur and sulfates on the
soil solution; (2) effect of sulfur on the solutions of different soils;
(3) determination of the minimum optimum concentration of sulfate
for alfalfa by the water culture method; (4) confirmation of field-plat
trials.

The soils employed and some of their characteristics are given in
table 1.

1927]

Powers: Studies of Sulfur in Belaiion to the Soil Solution

125

EELATION OF BEPLACEABLE BASES AND SULEOFICATION TO THE

SOIL SOLUTION

The soil characteristics presented in table 1 indicate the amount
of soil solution these soils can retain, their total sulfur content, sulfur
oxidizing power, the sulfate content of their displaced soil solutions,
the nature and amount of replaceable bases contained, and the
response of these soils to sulfur treatment.

TABLE 1

Some Characteristics of the Soils Used

Soil series and type

Usable
water
capacity
(approx-
imate),
acre-ins.

per
acre-ft.

Total

sulfur,

lbs. to

2,000,000

Sulfur

oxidized

in 14

days,

per cent

Sulfates
displaced

soil

solution,

p. p.m.

Replace-
able

bases,
per cent

of soil
Ca, Mg,

Na, K

Replace-
able
calcium
per cent
of soil

Response
to sulfur
in field

%"

2"

l'A"

2V2"

821
240

36
17
15
18

10
4
3

140

32
464

64
168

14*

12«
117t

.0613

.1734
.7941
.2322
.1967

4153

.2876

1 0816

.0400
.1248
.6512
. 1419
.1383

.3654
.2600
.8624

Good

2. Umatilla med. sand ...

Slight

4. Yakima sandy loam

5. Deschutes sandy loam

6. Willamette silty clay
loam

403

680
280
400

Good
Very good

Slight

8. Antelope clay adobe.

Very marked

* Growing crop May 7.

t 2:1 extract.

The sulfofying power of a soil seems to have a closer relation to
the sulfate content of the soil than does the total sulfur supply.
Halversen and Bollen21 have shown the relation of sulfur oxidizing
power of soils to sulfate content. As sulfofication is largely a biological
process, providing conditions most favorable for the organisms should
aid in maintaining a favorable sulfate concentration in the soil
solution. Application of manure with sulfur has appeared to be an
effective aid to sulfofication in treated alkali land.30 Burd has
recently reported data8 emphasizing the importance of biological
activities in keeping up a favorable concentration of nutrient anions
and the importance of supplying sufficient total anion concentration
to hold favorable amounts of cations in the soil solution. Johnson31
seems to show that growing alfalfa may increase the sulfate-supplying
power of a soil. This may be due to plant removal of sulfate formed.
The forms of sulfur in a soil may affect rate of sulfofication.

The total supply of replaceable bases and the proportion of
univalent to multivalent bases adsorbed may indicate the power of

126 University of California Publications in Agricultural Sciences [Vol.5

recovery of a soil solution after exhausting crops and the properties
likely to be imparted due to base exchange reactions. Sulfur may
oxidize and then unite with water to cause an increase in hydrogen
ion concentration in the soil solution. The presence of readily soluble
compounds, such as calcium carbonate, under such a condition will
favor solution, the rate of which will depend on the concentration of
acid present. Twentieth normal hydrochloric acid in large quantity
has been found to be capable of replacing about all the replaceable
base held by the soil adsorbing complex where drainage is provided.17
When the concentration of hydrogen ion or other cation is increased
as a result of sulfur oxidation, base exchange may occur. This is
sufficient to indicate the close and important relation of sulfur oxida-
tion, solubility effects, and base exchange reactions in the soil system
to changes in its liquid phase. Where the supply of replaceable cal-
cium in table 1 is low and response from sulfur applications marked,
it would seem to indicate that sulfur oxidation results in solubility
effects.

Soils 2 and 6 (table 1) give little response to sulfur applications,
and these soils oxidize sulfur rapidly. Soil 2 is irrigated with water
containing two or three pounds of sulfate sulfur per acre-foot. Soil 8
oxidizes sulfur slowly and gives marked response to sulfur appli-
cations.

In order to learn the chemical effects of sulfur and sulfates on
the soil solution twenty-eight two-gallon stoneware jars that had
been coated with valspar were filled with screened surface soil of
Madera sand type which was known to give typical response to sulfur
applications. These were divided into groups of four and treated
with different salts (table 2) at a rate sufficient to supply one hundred
pounds of sulfur an acre. Three jars of each group were planted to
Grimm alfalfa while the fourth was fallowed. Before the seedlings
were one inch high, their number was reduced to ten uniform sized
plants in each jar. The soil was maintained at about optimum
moisture content by frequent additions of distilled water and the
fallows periodically sampled and screened and their solutions dis-
placed and analyzed, using methods described by Burd.11 Displace-
ment of the soil solution is accomplished by packing the soil in brass
tubes, adding distilled water above as a displacing medium, and then
air pressure from the top.

Methods of analysis employed were, for the most part, those in
use in the plant nutrition laboratories of the University of California

1927] Powers: Studies of Sulfur in Belation to the Soil Solution 127

and recently made available by Hibbard.25 The water culture tech-
nique employed has been described by Hoagland,28 Gericke,18 and
Davis.14 Hydrogen ion concentration determinations of solution
cultures were colorimetric and of displaced soil solutions Avere electro-
metric. Successive portions of displaced solutions were found to show
fairly uniform electrical conductivity or specific resistance until
dilution by the displacing medium began, at which point displacement
was terminated, the dilute solution discarded, and the uniform
solution saved and analyzed.

CHEMICAL EXPERIMENTS

SULFUR AND SULFATES AND THE SOIL SOLUTION
Table 2

The treatments given to portions of soil are indicated in column
1, table 2. Sulfur was added at the rate of one hundred pounds per
acre, while calcium oxide and sulfates were added in quantities con-
tained in gypsum equivalent to one hundred pounds sulfur an acre.

The composition of the soil solutions displaced from treated and
untreated fallow jars of Madera sand as determined in parts per
million, after 6 weeks' and again after 12 weeks' incubation, is pre-
sented in table 2. Analyses are also given for the solution displaced
from the original soil and for the two lots receiving heavy sulfur
applications after 15 months.

The reaction of this soil on the untreated field plats was slightly
alkaline and gave a pH value of 7.3. Soil from sulfured field plats
was found to be exactly neutral. After 6 weeks' incubation in the
green house a very slight acidity had been developed in untreated,
fallow jars, as shown later (table 6), perhaps owing to formation of
carbonic acid from decomposition of organic matter under the moist,
warm conditions in the greenhouse. After 6 weeks' time the develop-
ment of a slightly higher concentration of hydrogen ions A\ras observed
in soils that had been treated with sulfur or with certain sulfates.
The concentration of sulfate ion in the solutions displaced in such
cases was found to have increased. After 12 weeks' incubation the
hydrogen ion concentration had increased with certain sulfate treat-
ments, and the heavy sulfur application resulted in hydrogen ion
concentrations that were unfavorably high for growth. This high
acidity .still prevailed after 15 months. In the cropped series definite

128

University of California, Publications in Agricultural Sciences [Vol.5

acidity developed and growth appeared to maintain a hydrogen ion
concentration of about pll 6.0. Reaction might be modified by decom-
position of organic matter, excretions by roots, formation of sulfuric
acid in sulfur treated pots, as by hydrolysis, and selective absorption
of cations, added in certain salts such as sulfate of ammonia.

TABLE 2
Effect of Sulfur and Sulfate on the Soil Solution
Analysis reduced to 10 per cent moisture (wet weight).

Initial soils

Dec.

Parts per million soil solution

Treatment, pounds per acre

pH

N03

SOj

PO,

Ca

K

Mg

7.3

7.0

47
25

140
194

4 5
3 5

119
146

57
83

129

78

Analysis of fallows (after six weeks incubation)

X untreated

Sulfur, 100 lb.

CaO

SandCaO

K2SO(

CaSd

X

(NH,)2S04

MgS04

Displaced soil.

S-200

S-500

6 2

116

253

4 0

144

98

6 1

161

369

3 5

203

125

6.5

127

195

6 0

142

88

6.3

156

256

5 0

196

105

6 1

157

294

3 0

116

172

6 3

120

247

3 5

135

112

6 7

70

161

4 0

172

60

5 4

150

205

4 0

227

63

5 9

53

235

4 5

294

63

6 5

. 30

153

4 0

160

27

5.S

38

284

5 0

327

125

5 9

21

509

3 5

349

133

119
221

95
156
113

90

91
121
196

98
119
102

Second analysis (after twelve weeks)

X

s

CaO

CaO and S.

K0SO4

CaSO,

X

(NHO2SO4

MgSO<

Displaced soil
S-200
S-500 ...

6 1

124

261

3 0

207

107

6 3

100

341

5 0

382

72

6.7

102

204

5 0

324

127

6 7

77

322

5 0

356

120

6 5

81

282

4 0

361

165

6 6

82

224

4 0

351

84

5.8

87

190

4 0

139

47

5 6

176

258

5 0

326

57

5 6

79

241

4 0

268

64

6 4

88

219

3 5

124

32

4 8

47

376

24 0

376

135

4 4

37 '

52 0

156

160
131
118
144
165
79

139
128
183
14S
157
171

Third analysis (after fifteen months)

X

S 200

7.7
3 8
3 6

44

24

1

94
672
1510

2 0

1 0

15 0

79
152
171

70
174
319

S 500

1927] Powers: Studies of Sulfur in Relation to the Soil Solution 129

The nitrate in field plats, treated with 200 pounds of sulfur per
acre about a year previous to sampling, was lower than in the adjacent
untreated plat. After incubation for 6 weeks there was a tendency
toward accumulation of nitrates except where unfavorable acidity had
developed. After 12 weeks, high acidity developed in heavily sulfured
jars, which made conditions unfavorable for nitrification and de-
pressed the supply of nitrate to or below that of the untreated soil.
A large portion of the nitrogen in the ammonium sulfate applied
appeared later as nitrate.

An initial supply of 140 parts per million of sulfate was found in
the soil solution. Since this soil will retain about 10 per cent useable
moisture between the wilting point and the excess point, this repre-
sents 14 parts per million sulfate for the whole system. Sulfur in
the field trial increased the sulfate content to 194 parts per million.
Madera sand appeared to have good sulfofying power, even with-
out sulfur additions. Addition of sulfur and sulfate substantially
increased the sulfate content of the soil solution in six weeks. Add-
ing calcium oxide with sulfur appeared to retard, rather than to
encourage, sulfofication. Sulfofication appeared to be somewhat
proportional to the amount of sulfur applied, for in subsequent
determinations gains in sulfate concentration were found. Small
differences were found from the application of various sulfates.

The amount of soluble phosphate first seems to increase, then to
decrease, after sulfur treatment. There appears to be a little depres-
sion in the amount of phosphate in the solution after sulfur applied
has brought considerable calcium into solution. With heavy sulfur
applications, marked increase in acidity and increase in the amount
of phosphate were found in the soil solution after 12 weeks' in-
cubation. Increase in solubility of bases such as calcium, iron, or
aluminum appears to have resulted in precipitation of phosphate
before 15 months passed.

Calcium was found to come into solution strikingly as a result of
sulfur or sulfate applications. Nearly three times as much calcium
was found in the soil solution following heavy applications of sulfur.
Sulfur appears to have modified the soil solution with respect to
calcium more than with any other ion.

Potassium was brought into solution in the soil to the extent that
the supply in solution was almost doubled by heavy applications of
sulfur. Part of the potassium, when applied as potassium sulfate,
appeared to be fixed by exchange reaction with other bases which

130 University of California Publications in Agricultural Sciences [Vol. 5

were brought into solution. Heavy application of sulfur resulted in
a large increase in potassium ion in the soil solution after 15 months.
Either potassium-bearing compounds were slowly dissolved or the
calcium had participated in a base exchange with the potassium in
the solid phase.

Magnesium ion has a tendency to increase in concentration in the
soil solution owing to sulfur additions and possibly also to base ex-
change reactions following an increase in total concentration of the
soil solution.

The analyses in general indicate that a very important function
of sulfate is that of bringing in and holding bases in solution. It
also appears to increase the soil acidity with a resulting increase in
availability of phosphate. The phosphate, however, may tend to dis-
appear if the soil is well supplied with bases, such as calcium, which
may react on the calcium and cause precipitation of phosphate from
the soil solution. This reciprocal relation of soluble calcium relative
to phosphate has been noted by Burd.9

SULFUR AND SOIL SOLUTIONS OF DIFFERENT SOILS

Table 3

Samples of typical Oregon soils were collected from old sulfur
experiment fields, including soil from both sulfured and unsulfured
plats, that had been in experiments for as long as ten years and had
received sulfur generally at the rate of one hundred pounds per acre
every three or four years. These samples were screened and brought
to optimum moisture content, allowed to stand so that equilibrium
would be established between the solid and liquid phases of the system,
and the displaced soil solutions recovered and analyzed.

Results are given in table 3 and show that sulfur applications
increase acidity in all cases, and usually more than 0.5 pH. There
was a noticeable difference in the buffer value of various soils used.
The Catherine loam did not resist change in reaction well and became
unfavorably acid. The nitrate content of these solutions was not
greatly modified, but gave evidence of being depressed in certain
cases from sulfur applications on acid soils, as shown in the case of
Catherine loam.

The sulfate content of Willamette and Carlton soils was found to
be very low. Samples were taken from these soils on May 7 following
a cool spring, which would be unfavorable to sulfur oxidation, and
from plats supporting winter grain that had attained 5 to 9 inches

1927J

Powers: Studies of Sulfur in Relation to the Soil Solution

131

height. Both these humid soils are subject to leaching in winter.
Sulfofication is rapid under laboratory conditions in the Willamette
soil and little crop increase results from sulfur applications thereto,
while Carlton soil is lower in total sulfur and sulfate and responds
to sulfur applications. Sulfur substantially increased the sulfate
content of all soil solutions. There was a tendency for sulfur to
increase the calcium content of the soil solution, and also the potassium
content.

TABLE 3

Effect of Sulfur on Soil Solutions

Soils displaced May, 1925, reduced to comparative moisture basis.

Soil

Treatment

pounds per

H2O

pH

N

SO4

po4

Ca

K

acre

200 S. Ac.

10%

(wet

24

672

152

174

basis)

200 S. Ac.

10

7 00

25

194

3 5

146

83

Untreated

10

7 30

47

140

4 5

119

57

3 x 100 S.

15

7.47

51

316

1 0

123

96

Untreated

15

7 84

63

153

10 0

100

29

3 x 100 S.

10

7 00

54

58

3 0

86

31

Untreated

10

7 76

36

37

3 0

86

25

100 S.

15

6 83

20

103

2 0

211

86

Untreated

15

7 67

40

75

4 5

164

75

2 x 100 S.

20

6 15

18

207

2 0

95

75

Untreated

20

6 83

15

13

1 0

41

58

3 x 320 S.

20

5 81

trace

46

1 5

42

14

Untreated

20

6 14

none

17

4 0

45

11

100 S.

30

5 47

22

555

3 0

328

318

Untreated

30
Fe

6 57

18

114

2.0

142

256

Untreated
3 x 200 S.
3 x 400 S.

.04
08
07

117
100
74

3 8

3 0

4 6

100
105
152

20 3
17 3
14 8

Mg

Madera sand field sample

1. Madera sand

2. Madera sand

3. Deschutes sandy loam

4. Deschutes sandy loam

5. Umatilla medium sand

6. Umatilla medium sand

7. Yakima sandy loam

8. Yakima sandy loam

9. Carlton silt loam

10. Carlton silt loam

Wheat 5" May 7.

11. Willamette silty clay loam

12. Willamette silty clay loam
Barley 9" May 7.

13. Catherine loam

14. Catherine loam

Water extract, two to one.

15. Antelope clay adobe

16. Antelope clay adobe

17. Antelope clay adobe

78

129

Willamette silty clay loam and Carlton silt loam are acid soils,
the latter occurring in the low foothills of the Willamette Valley. The
Willamette soil from the old valley filling contains a fair total amount
of sulfur, and this soil has a high sulf ofying power and good supply of
organic matter. It gives only slight response to sulfur applications.
Carlton and other "redhill" soils are low in total sulfur and in soluble
sulfate and give moderate response to sulfur treatment. They are
also low in soluble calcium, and in some instances the soluble potassium
is low. Sulfur may help to bring bases into solution in these acid
soils, but calcium sulfate may be more safely used.

132 University of California Publications in Agricultural Sciences [Vol. 5

Umatilla medium sand receives from two to three pounds of sulfur
in each acre foot of irrigation water and requires at least five acre-feet
of water a season. This soil is rather low in replaceable bases and
does not afford much opportunity for base exchange. It gives slight
response to sulfur applications. On the finer soils in that region a
moderate increase in alfalfa yield is secured from sulfur applications.

Catherine loam has given more profitable returns from calcium
sulfate than from sulfur. The reaction of this soil is already slightly
acid and sulfur may develop an unfavorably acid condition. This
was formerly wild meadow land.

Yakima sandy loam and Deschutes sandy loam are arid soils of
nearly neutral reaction with large total supplies of calcium and having
only moderate amounts of potassium ion in their soil solutions. The
former is typical of the main soil area of Klamath Project. Potassium
salts pay when applied to Deschutes sandy loam in which potatoes are
growing, and sulfur appears to bring treble the amount of potassium
into the soil solution in this soil. The alfalfa crop in this section when
soil-treated with sulfur develops an especially rich green color.

The samples of Antelope clay adobe used in these experiments
come from the sulfur fertilized plats established by F. C. Reimer north
of Medford and are too heavy for displacement, so water extracts were
made. The amount of iron in solution was doubled by sulfur applica-
tions and there was some increase in calcium ion in solution. Iron
pyrite on this land has given as good increase in alfalfa yield as
sulfur, after time was allowed for oxidation of the pyrite. Ferrous
sulfate has given the best yields in plat trials at this experiment
field.50

After the analyses above given were completed, ferric chloride was
sprayed on two plats of alfalfa previously unfertilized and a vigorous
growth resulted, showing all the visible results commonly secured
from sulfur on this field. There is a possibility of iron participating
in a base exchange but that does not seem to have been an important
factor here. Iron sulfate has been successfully used to overcome
chlorosis in fruit trees where applied at the tree roots in this heavy
soil.

The chief effect of sulfur may depend considerably on the char-
acteristics of the particular soil at hand and its reaction, physical
condition, chemical composition, or micro-organisms present. On arid
soils of slightly alkaline reaction sulfur may improve the reaction of

1927] Powers: Studies of Sulfur in Relation to the Soil Solution 133

the soil solution for alfalfa. This may increase the solubility of iron
in the soil solution and favor the development of chlorophyll. It may
also favor the absorption of anions, such as nitrates, by plants. A
better supply of calcium, as -well as sulfate, is often provided by an
application of sulfur.

SULFUR AND ALFALFA YIELD WITH SOILS IN JARS

Four portions of each of these soils were arranged in one-gallon
jars, two being treated with sulfur at the rate of one hundred pounds
an acre, the others untreated. One treated and one untreated jar
containing soil of each type were then planted to alfalfa for culture
tests and for displacement and analysis, if needed, to check against
field plat samples.

The increase in yield of alfalfa secured in these jars as a result
of sulfur treatment ranged from 7 per cent to 54 per cent. Umatilla
sand appeared to give greate" response to this treatment, in the jars
and irrigated with distilled water, than under field conditions Avhere
large amounts of irrigation water contributed a substantial part of
sulfur needed by the alfalfa. Ferric chloride was found to be about
i ■ effective as sulfur on Antelope clay adobe, for increasing alfalfa
yield in jars, which is further evidence that an important effect of
sulfur on this soil is to improve availability of iron and overcome
chlorosis in alfalfa grown in it.

A preliminary experiment was conducted with young alfalfa
transplanted from Madera sand soil from near Delhi, California.
These plants had grown through the summer season on soil receiving
no sulfur. Three two-gallon jars were untreated, a second lot of three
received sulfur, a third lot, reprecipitated calcium carbonate and
sulfur, a fourth received, sulfur as calcium sulfate, and the fifth lot
received potassium sulfate at a rate that would supply one hundred
pounds of sulfur to the acre. The plants were set out December 29,
1923. Cuttings were made when the growth bloomed freely, February
29, May 5, and May 27. One jar of each lot was not harvested at the
second cutting but was left for seed. The effect of sulfur was to favor
seed formation. Sulfur or sulfates increased the height, vigor, and
yield of alfalfa in this trial 20 to 40 per cent.

Sulfur reduced the water requirement about one-third, as ex-
pressed in units of water per unit of dry matter.

134 University of California Publications in Agricultural Sciences [Vol.5

Thirty-six two-gallon stoneware pots, paralleling the fallow jars
used for analyses, were planted to Grimm alfalfa, thinned to ten
plants per jar and four months' growth harvested in one cutting May
27, 1924. All the sulfates were applied in amounts needed to provide
one hundred pounds per acre of sulfur and gave similar increases in
yield. The jars receiving potassium sulfate attained the maximum
height. Moderate increases over the untreated pots were secured with
calcium and with sulfur used singly or combined. The increased
efficiency of water consumed by this growth in treated jars was
reflected in a lower water requirement per unit dry matter. A more
favorable concentration of soil nutrients or better balance in the
solution should lead to a lower transpiration and therefore a lower
water requirement, unless other conditions cause small yield of dry
matter.

HYDROGEN ION CONCENTRATION IN CROPPED AND FALLOW

SOIL POTS

The hydrogen ion determinations were made about every two
weeks for all soil in jars. Colorimetric tests were made promptly,
after sampling, with fresh color standards checked with the hydrogen
electrode.

Decomposition of organic matter on untreated fallow pots seems
to have brought the reaction down from pll 6.9 to about 6.2. Calcium
carbonate tended to maintain a more nearly neutral reaction, while
heavy application of sulfate developed an unfavorably acid condition.

Cropped pots when untreated developed a slight acidity and main-
tained a pll of about 6.0. There was a somewhat more uniform
reaction in cropped pots due perhaps to the tendency of plants to
maintain a favorable reaction. Results strongly indicate that a
slightly acid reaction is brought about by C02 evolved by growing
roots in cropped pots or from decomposition of organic matter in
fallows forming HCOa as suggested by Hoagland.JS They also indi-
cate that a slightly acid reaction is most favorable for alfalfa growth
in soil and that moderate applications of sulfur may improve the
reaction of basic or slightly alkaline arid soils for alfalfa nutrition.

1927] Potcers: Studies of Sulfur in Relation to the Soil Solution 135

PHYSIOLOGICAL EXPERIMENTS

In order to test the adequacy, for alfalfa growth, of sulfate
concentrations found in soil solutions, some supplementary water
culture experiments were undertaken. It was hoped that this would
shed further light on the sulfate need of alfalfa, the form in which
sulfate is best obtained from the soil solution, the part of the growth
period when sulfate is most needed, the crop-producing power of
limited amounts of sulfate, and especially the concentration of sulfate
needed for best growth. For this work fruit jars were used and the
seedlings supported on flat perforated corks. Molal solutions were
prepared of di-potassium acid phosphate, mono-potassium acid phos-
phate, calcium nitrate, and magnesium sulfate. Prom these stock
solutions a culture solution was made up to an osmotic concentration
equal to approximately 1 atmosphere pressure and a pll value of
about 6.0. Sulfur-free culture solutions were provided by substitut-
ing calcium nitrate for magnesium sulfate, and limited amounts of
sulfate were added in certain experiments from a saturated solution
of calcium sulfate to provide the number of parts per million of sul-
fate desired. A fresh solution of iron-tartrate was used for supplying
soluble iron. In these experiments records were kept of the height
and vigor of plants, the amount of transpiration, and the reaction to
culture solutions. The reaction tests were made almost daily where
there was a tendency to deviate from the optimum range.

Preliminary Studies
Tables 4 to 8

Two-year-old alfalfa plants were secured from sulfured and un-
sulfured field plats near Delhi, where crops grown on Madera sand
had shown typical response to sulfur. The crowns of plants grown
on sulfured fields were much larger than those of the same age from
the unsulfured plats. The color of foliage on sulfured land was a
dark green, the plants presenting a marked contrast to the rather
chlorotic, unthrifty plants from the unsulfured plats. Sulfur in this
field trial had doubled the yield of alfalfa. The plants Avere washed

136 University of California Publications in Agricultural Sciences [Vol. 5

free of soil, dried on a blotter, and their individual weights deter-
mined. There had been some root pruning so the tops were clipped
back close to the crowns. The plants recovered promptly from trans-
planting when placed in the nutrient solution.

TABLE 4

Alfalfa Transplanted from Sulfur-Treatfd Land

Mean yield in grams. Dry matter (3 cuttings) from single two-year-old plants.

Water
Mean yield tops, requirement

Treatment grams tops

A — Four-quart jars. Plants from sulfured field.

Complete solution 8.4± 10 533

Solution lacking S 4 5± 16 801

B — Three-quart jars. Plants from unsulfured field.

Complete solution ..... 5 1± 24 589

No S. Two nitrates 1 9± 08 1377

C — Two-quart jars.

Complete solution 4.5± 24 612

NoS. Two phosphates 2 1± 07 1285

D. I— Reaction adjusted April 1, with N/10 HsSOi.

Complete solution 2 4± 12 780

NoS. Two nitrates 1 6± 05 1067

NoS. Two phosphates 1 5± 02 1089

D. II— Reaction adjusted April 1, with N/10 HC1. (Whole plant.)

Complete solution ..... 1 9± 06 598

NoS. Two nitrates 1 4± 06 754

NoS. Two phosphates 1 5± 08 751

A trial was made with twelve plants from the unsulfured field
plat, the plants being divided evenly into two lots according to weight.
Six plants were placed on four-quart jars containing complete culture
solutions and six others on solutions lacking sulfur. In two weeks a
difference in the appearance of the plants was noticeable. The plants
provided with sulfate developed a better green color and made over
twice the growth during the first two months compared with those
grown in the sulfur-free solution. The plants came into bloom and
were cut January 29, April 23, and May 27, 1924. The yields are
presented in table 4, section A. Approximately twice the yield of
dry matter was secured from plants grown on solutions provided with
sulfate. These plants made nearly twice as efficient use of water
consumed for each unit of dry matter produced as did the sulfur-free
series.

A second lot of plants were set on three-quart jars and treated
as in the above experiment, except that the sulfur-free solution in-
cluded two nitrate salts instead of two phosphate salts as in the above

1927]

Powers: Studies of Sulfur in Relation to the Soil Solution

137

138 University of California Publications in Agricultural Sciences [Vol.5

trial. The presence of two nitrate salts, or a larger supply of nitrates,
was associated with greater yields relative to untreated plants than
was secured in the above experiment (table 4, B) . These transplants
were one year old and sulfur about trebled the yield, resulting in a
transpiration requirement of about three-sevenths of that from the
plants grown in sulfate-free solutions.

A third lot of transplants from the unsulfured alfalfa plats were
divided into lots of six and placed on two-quart jars, one-half being
provided with a complete culture solution and the others with a
solution lacking sulfate. The yields of these plats are presented in
section C of table 4. Where sulfate was provided the plants outgrew
their chlorotic appearance in two to three weeks' time, indicating that
lack of sulfate was the cause of their devitalized condition. The total
yield for plants provided with sulfate was more than twice that from
the sulfur-free series for three cuttings, and consumed less than half
the amount of water per unit of dry matter produced.

A fourth lot of transplants two months old was secured without
root injury and set on three dozen, one-quart culture jars. One dozen
of these jars were provided with a complete nutrient solution; a second
dozen were provided with a water culture solution lacking sulfate
and containing two nitrate salts; and the third dozen were provided
with nutrients using two phosphate salts. When these plants were six
weeks old they developed a chlorotic appearance, and at that time
half of the dozen plants in the sulfur-free solution were brought to a
favorable reaction by the use of N/10 sulfuric acid. To six other
cultures N/10 hydrochloric was applied to produce a favorable re-
action. Results of this trial, table 4, section I), show a marked increase
in yield where sulfate was included. Applying a limited quantity of
sulfate, when plants had been grown for six weeks on culture solutions,
produced more improvement than can be credited to improved reaction
alone. In all these trials the water consumption was greatly increased
where sulfur was lacking. In three days' time the sulfate added in
acid caused a dark green color of the foliage, which was noticeable
until the plants were harvested a month later. This difference is indi-
cated in figure 3.

1927]

Powers: Studies of Sulfur in Relation to the Soil Solution

139

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a org

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TO

140 University of California Publications in Agricultural Sciences [Vol.5

C
02

1927] Powers: Studies of Sulfur in Relation to the Soil Solution 141

SULFUR AND CHLOROPHYLL

Chlorophyll determinations, following methods described by
Willstatter, with the whole top growth from sulfured and unsulfured
alfalfa in soil pot trials, yielded 12 per cent more chlorophyll where
sulfur was applied. Alfalfa leaves collected from sulfured and un-
sulfured field plats showed an increase of 18 per cent in chlorophyll
content. The effect of sulfur in increasing width, size, and color of
alfalfa leaves is indicated in figure 2. Lack of sulfur resulted in a
lack of rich green color and lack of vigor. Data in table 3 show that
sulfur application increased the iron content of the water extract
from Antelope clay adobe and this iron is known to play an important
role in chlorophyll synthesis. Sulfuric acid was also found to restore
color better than hydrochloric acid when used to adjust reaction in
culture solutions.

WATER CULTURE EXPERIMENTS WITH SEEDLINGS
Table 5, A

To check the plan of providing sulfate to seedlings in partial
culture solutions two days in six, three series of cultures were pro-
vided. In the first, plants were exposed to calcium sulfate one day
in five ; in the second, two days in six ; and in the third, four days
in eight. The remainder of the period the plants grew on culture
solutions lacking sulfur. During the first two months of the experi-
ment the best growth was obtained with plants exposed to calcium
sulfate two days in six. In the latter part of the growth period the
plants exposed to sulfate only one day in five forged ahead and gave
definitely better total yields both of total and marketable dry matter,
indicating that extra sulfur was most helpful in the early part of
the growth period and perhaps undesirable later. Figure 6 shows
typical plants of each series after three months' growth. There was
little difference in the yields of the plants exposed two days, compared
to those exposed four days to sulfate solution, as shown in section A
of table 5. There was a marked difference in appearance of plants
with and without sulfur in this and other trials, as shown in figure 7.

142 University of California Publications in Agricultural Sciences [Vol. 5

HOW DOES SULFUR GO INTO THE PLANT?
Table 5, B

Sixteen series of six cultures each containing three Grimm alfalfa
seedlings per culture were* employed in an experiment, which covered
a growing period of 110 days. Plants were grown on culture solutions
lacking sulfur four days in six and on various partial culture solutions
containing different sulfates two days in six. Solutions were changed

TABLE 5

How Does Sulfur Go Into the Plant?

Alfalfa yield in grams. Dry matter. May 26, 1924.

(Grown on sulfur-free culture solutions and transferred to solutions containing

sulfate at regular intervals.)

Mean yield

Whole Water

A. Treatment culture Tops requirement

3 plants tops

Complete culture solution, unchanged 3.1 2.2± 08 855

Complete culture solution, changed monthly 3 9 2 4±15 867

S-free solution, unchanged 3 8 2 2± 16 851

S-free solution, changed monthly 4 1 2 6± 10 712

S-free solution 4 days; then CaSOi 1 day 5 7 3 9± 23 569

S-free solution 4 days; then CaSC>4 2 days 4 2 2 7± 14 790

S-free solution 4 days; then CaS04 4 days 4 5 2 9± 23 651

B.

S-free solution 4 days; then (NHOsSCU 2 days 3 6 2 7± 21 725

S-free solution 4 days; then MgSOi 2 days 18 1 2± 10 796

S-free solution 4 days; then K2SO4 2 days 5 3 3 6± 18 635

S-free solution 4 days; then Ca, N03, SO4 and PO4 2 days 5 5 3 6± 13 639

S-free solution 4 days; then Mg, NO3, SO4 and PO4 2 days 9 2 8± 69 1875

S-free solution 4 days; then K, NO3, SO4 and PO4 2 days 4 6 3 3± 23 699

S-free solution 4 days; then Ca, NChand SOi 2 days 4 6 3 3± 06 691

S-free solution 4 days; then Mg.NOs and SO4 2 days 13 1 0± 16 1149

S-free solution 4 days; then K, NO3 and SO4 2 days 3 6 3 3± 21 638

C. Solutions free of K and SO4 vs. — (Cation supplied only 2 days in 6 and with SO4)

S-free solution 4 days; then CaSOj 2 days

S-free solution 4 days; then K2SO4 2 days
S-free solution 4 days; then (NH4>2S04 2 days ...

Complete solution

S-free solution 4 days; then (NHMsSCU (grain) 2 days
Displaced soil solution (6 weeks' growth)
Displaced soil solution plus K2SO4

frequently during the latter part of the growth period to avoid con-
tamination by moving the plants from the sulfur-free nutrient solution
to the companion solutions containing different forms of sulfate. The
plant roots were washed by standing them in two-gallon jars of tap
water for twenty or thirty minutes and then rinsing in distilled water
before transferring from one partial solution to the other. An extra
series of stationarv controls having sulfur, and one lacking sulfur.

4 3

2 9± 11

421

2 9

1 7± 10

603

.3

2± 02

6666

3 5

2 5± 10

603

6 7

5 5± 30

539

15

l.li.ll

750

6

,2± 03

937

1927] Powers: Studies of Sulfur in Relation to the Soil Solution 143

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14-1 University of California Publications in Agricultural Sciences [Vol.5

were provided to test the effect of changing the nutrient solutions
monthly. Changing the solution showed a little advantage, as did
changing the plants. This was probably due to improved aeration.

Two days in six, series 8 to 12 received sulfate in single salt solution
as calcium sulfate, potassium sulfate, ammonium sulfate, or mag-
nesium sulfate, respectively. During the first two months of this
experiment plants receiving sulfate in the form of calcium sulfate
were definitely the better plants. During the last four or five weeks
of the experiment these were overtaken by the potassium sulfate series,
the yield of which was slightly greater. The yield with ammonium
sulfate was about four-fifths of that with the calcium sulfate, while
the magnesium sulfate scries yielded only about two-fifths as much
as the calcium sulfate series.

Series 12 to 14 were provided in which the sulfate-bearing solution
received nitrate, phosphate, and sulfate salts of the base under con-
sideration. Under this condition calcium salts produced one-eighth
more total dry matter than the potassium salts. The yield with mag-
nesium sulfate was very low.

In series 15 to 17 the cations were supplied in both nitrate and
sulfate forms. There was no significant difference in the yield ob-
tained with potassium from that obtained with calcium sulfate.

In all trials, solutions containing magnesium salt gave very poor
results. The reaction was difficult to control in the case of magnesium
salt solutions, and even with reaction controlled there appeared to
be magnesium toxicity. During the first two months of the growth
period, calcium sulfate appeared to be definitely the best form of
sulfur for the alfalfa plants. For typical plants, the relative growth
for different treatments is shown photographically in figure 4.

During the latter part of the growth period potassium sulfate
showed advantage in certain cases.

CALCIUM SULFATE VEESUS POTASSIUM SULFATE
Table 5, C
An experiment was arranged to compare further the value of
calcium sulfate with that of potassium sulfate. In this experiment
the main solution was deprived of both sulfate and the cation con-
cerned, so that it could be obtained only during the two days out of
six when the roots were in the partial nutrient solution containing
sulfate. Thus calcium, potassium, or magnesium was held out of the
main solution and applied only as sulfates in the partial nutrient

1927] Powers: Studies of Sulfur in Relation to the Soil Solution

145

146 University of California Publications in Agricultural Sciences [Vol.5

solutions to which plants were transferred two days in six. Also nitro-
gen, as well as sulfur, was kept out of a certain main solution, being
provided only two days in six as ammonium sulfate. In this experi-
ment potassium sulfate gave only about three-fifths the yield of tops
and of total dry matter as was secured with calcium sulfate. In this
trial nitrogen and potassium were not present at one time, and the
calcium sulfate excelled during nearly all of the growth period, as
shown in figure 5. During the period when the plants were nine to
ten weeks old, the potassium sulfate series and calcium sulfate series
were nearly equal in size.

In connection with the value of potassium sulfate relative to
calcium sulfate, it should be noted that calcium encouraged nmch
branching of roots and a bushy top growth, or cell division ; whereas
potassium produced cell elongation and seemed more important at
that period of growth when the alfalfa was making its maximum in-
crease in height. The ash of alfalfa contains about 16.25 per cent
calcium and 24.7 per cent potassium and the oven dry alfalfa, 1.26 per
cent calcium as against 1.87 per cent for potassium.32 As shown by
Gericke18 potassium is best supplied to plants in association with
nitrate, and this was verified in the course of these experiments.

COMPLETE NUTRIENT SOLUTION VERSUS DISPLACED SOIL

SOLUTION

Table 5, C

In connection with these experiments, three series of 400 cc. bottles
were provided, set with two alfalfa seedlings to each culture. One
set was filled with a complete nutrient solution, the second with the
natural soil solution displaced from the Delhi soil, and the third series
with displaced solution reinforced with sulfate applied as potassium
sulfate. After the first few weeks the displaced solutions made little
further progress. The series reinforced with sulfate yielded about
three times as much dry matter as the natural soil solution, but only
about one-fifth as much as the control. At Oregon Experiment Station
sulfates have increased growth on lysimeter waters even where the
untreated drainage water was changed frequently and where the
sulfate concentration in the percolate was similar to that obtained
from displacing the same soil type.59

A similar experiment, to be reported elsewhere, dealt with the best
salt for supplying calcium ion for alfalfa in partial solution cultures.

1927] Poivers: Studies of Sulfur in Relation to the Soil Solution

147

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148

University of California Publications in Agricultural Sciences [Vol. 5

The largest yields were secured with calcium supplied as sulfate. A
slightly lower yield was secured with calcium nitrate, and much less
with calcium phosphate. The mean weight of tops from six weeks'
growth was .96 gm. with calcium sulfate ; .80 gm. with calcium
nitrate, and .20 gm. with calcium phosphate.

WHEN DOES ALFALFA MOST NEED SULFUK?
Table 6

Six series of cultures were arranged to determine more definitely
the time in the growth period up to the blooming stage when alfalfa
makes the maximum demand for sulfur. Three series were started
in complete solutions while three companion series were in sulfur-free
solutions. After three weeks the first pair of series of plants was
reversed as to sulfur supply. The second pair was interchanged after
six weeks, the third pair at nine weeks. These plants were harvested
after twelve weeks ' growth. The advantage of having sulfate supplied
during the first six weeks of this growth period was still evident at
harvest time, as shown by figure 7.

In all three cases the plants started in the sulfur-containing
solution gave higher yields. There was some indication of benefit in
the case of plants removed from sulfur after six weeks, and there was
less recovery from lack of sulfur where this element was applied late
in the growth period.

TABLE 6

At What Stage in Growth Period op Alfalfa is Sulfur Most Needed?
Twelve weeks' growth period.

Culture

Treatment

Mean yield in grams

Water

series

Whole culture

Tops

requirement
tops

28

3 9
3.3
3 6

2 5

3 8
3.2

2 4± 16
2.3± 15
2 4± 12

1 8±07

2 7± 23
2 1± 12

430

28a

519

29

449

29a

714

30

411

30a

608

Solutions used in this trial were changed each month and analyzed.
The sulfate content for solutions containing an initial concentration
of 672 parts per million of sulfate at the end of the first month's
growth showed a decrease in concentration to 584 parts per million.
The solution being renewed, it was decreased in concentration to 450
parts per million the second month. A new solution was reduced

1927]

Powers: Studies of Sulfur in Relation to the Soil Solution

149

150

University of California Publications in Agricultural Sciences [Vol.5

to 612 parts per million the third month. The maximum absorption
of sulfur occurred in the second month and the minimum absorption
in the third month. From all indications, plants seem to require
sulfate largely during the earlier part of the growth period, pre-
sumably in building up their system after the seedlings have attained
some size. Sulfur applications may increase the sulfofying power of
a soil and residt in a more favorable concentration of sulfate ion at
critical periods of growth. In all these experiments, providing a
suitable sulfate supply gave a lower water requirement.

CKOP-PKODUCING POWEE OF LIMITED AMOUNTS OF SULFITE WITH

ALFALFA

Table 7

Eight series of solution cultures were prepared, including sulfur-
free controls and solutions containing 5 to 30 parts per million of
sulfur as calcium sulfate arranged in increments of 5 parts per
million. One part per million is equivalent to 1 milligram per liter
or practically the volume of cultures used. Maximum production per
milligram sulfur secured was .18 gms. alfalfa and with the solution

TABLE 7

Crop Producing Power of Limited Amounts of Sulfur

Dry matter yield in grains, six weeks' growth.

Series
No.

Treatment, approxi-
mate (mgm's S)

Mean yield
whole plant

Yield tops

Water
requirement

Inorganic S as
per cent SOj

42

No S

55
.92
1 02
1 15
1 06
.97
1 06

43± 04
.72± 03
78± 01
86± 05
82±04
82± 04
.78± 02

921
486
449
412
427
460
475

101

36

.086

37

10 p. p.m. S

.127

38

.223

39

20 p. p.m. S ...

.320

40

.238

41

30 p. p.m. S

.317

containing about 5 parts per million sulfur. Alfalfa plants were
grown thereon and when a month old showed a general increase in
growth up to the series containing 15 parts per million of sulfur.
With greater sulfate treatments the amount of growth was practically
uniform. When the plants were six weeks old, 10 parts per million
of sulfur appeared to be sufficient, as shown by figure 8. The plants
had attained 18 to 20 inches in height, and their requirement for
sulfur appeared to be somewhat diminished. There was indication
of a slight stimulating effect with 10 parts per million compared to

1927] Powers: Studies of Sulfur in Relation to the Soil Solution 151

152 University of California Publications in Agricultural Sciences [Vol.5

two or three times that amount at the later growth state, as shown by
figure 9. It was necessary to harvest before the plants were two
months old. The maximum yield was secured with 15 parts per
million of sulfur in the solution. That there was no significant differ-
ence between this and the control or the series receiving larger amounts
of sulfate is shown graphically by figure 12. The sulfur-free solution
there used was prepared from C. P. chemicals, but it was found to
yield 1.6 p. p.m. sulfur in the culture solutions as used.

Some soil solutions from Madera sand were found to contain 150
parts per million of sulfate. Their usable water capacity was less
than 10 per cent. An acre-foot of solution would not be stored in
less than 10 acre-feet of such soil, giving 11 parts of sulfate per million
in the total mass. In the soil, diffusion may be slower than in the
culture solution.

The last column in table 7 gives the sulfate recovered by hot water
extraction of plants grown in this experiment. A much larger amount
of unassimilated sulfate appears to have been present in plants grown
on solutions containing 15 p. p.m. or more of sulfur.

CONCENTEATION OF SULFATE NEEDED FOR OPTIMUM
GROWTH OF ALFALFA?

Evidence on the least probable concentration needed for optimum
growth is scarce. The concentration of different ions necessary in
solution cultures or soil solutions is not definitely known.

Cameron12 matured wheat in tap water which was claimed to
contain 0.5 parts per million of phosphorus as phosphate ion.

Burd10 suggested that, as a result of crop removal, the concentra-
tion in a soil solution may fall below supplying the need of certain
ions by plants. He reports a two-day nitrate supply as the lowest
concentration found under growing barley, as judged by the rate of
crop removal. It is further suggested that crop removal may hasten
solution from the solid phase of the system.

McCall and Richards42 found a higher concentration necessary in
quartz cultures to give equal effect with water cultures.

Hoagland and Martin27 point out that suitable concentration is
affected by size of culture vessel, plants to be grown, rapidity of
growth, reaction, and frequency of renewal of the solution.

In an experiment previously referred to, potassium sulfate greatly
increased the yield of alfalfa grown on displaced soil solution, although

1927] Powers: Studies of Sulfur in Relation to the Soil Solution 153

2

p

5'

3'
to

c
p
3

154 University of California Publication* in Agricultural Sciences [Vol.5

there was already an apparent abundance of potassium present. Cal-
cium sulfate or potassium nitrate increased the yield of grain grown
in lysimeter water in recent experiments at the Oregon Experiment
Station,50 even though the soil water was frequently renewed. The
study of crop-producing power of limited amounts of sulfate indicated
that 10 to 15 parts per million of sulfur or 30 to 45 of sulfate might
be needed for best growth of alfalfa. Two soil solutions studied
contained 12 and 14 parts per million respectively. An experiment
was planned to test the concentration of sulfate needed for alfalfa in
culture solutions, and also in a solid medium, as an aid in interpre-
tation of soil solution analyses.

SULFATE CONCENTEATION EXPERIMENT WITH CULTURE
SOLUTIONS

To study further the concentration of sulfate needed for optimum
growth of alfalfa, a new experiment was planned in which four series
of alfalfa plants were set up and grown in each concentration of
sulfate employed, so that one series from each lot could be harvested
at intervals of 10 days and subjected to chemical tests. Control series
were arranged without sulfur and with complete nutrient solutions.
The concentrations of sulfur in other series were 2, 4, 8, 16, 32, and
64 parts per million, respectively. Within 10 days the plants without
sulfur were making poorer growth than the remaining series. The
plants had been set on the jars when the fourth leaf appeared on the
seedlings. Up to 20 days' growth 16 parts per million of the element
sulfur in sulfate form caused a more rapid growth than a lesser con-
centration. Before the 30-day period a concentration of 8 parts per
million appeared to be sufficient and this condition obtained, so far
as could be judged by height and appearance of plants, to the close
of the experiment. The amount of growth for different concentrations
is indicated in figure 10.

INORGANIC SULFUR

To arrive at a procedure for studying the unassimilated or in-
organic sulfate in different lots of these plants at different stages of
growth, samples of alfalfa grown on field plats at Delhi were digested
for 8 hours, in one case with hot, and the other with cold water. The
pulp was filtered out, washed, and the extract acidified, redigested,
and filtered free from protein. The sulfate was then precipitated
with barium chloride, ignited, and weighed. Further tests were made

1927] Powers: Studies of Sulfur in Relation to the Soil Solution

155

3
o5'

%9

= 3

LA <f'

156 University of California Publications in Agricultural Sciences [Vol.5

by an additional 1 hours' digestion of the pulp, which indicated that
digestion with hot water for a period of 12 hours was desirable.

A second preliminary experiment was conducted on 1 gram por-
tions of alfalfa meal diluted with water up to 10, 25, 50, and 100 times.
Little advantage was found in diluting above 25 times and none above
50 times. Grimm alfalfa seed carried through this determination
yielded 0.3 per cent of sulfate.

The alfalfa grown in water cultures with limited amounts of
sulfate when analyzed by this method showed a rapid increase in
sulfate content up to 15 parts per million, a further gradual increase
up to 30 parts per million, and little or no increase thereafter (table
7 ) . In other words, the supply of inorganic sulf ates in these young
plants increased with the growth curve. Peterson48 and Hall20 seem
to find only a small portion of sulfur in alfalfa plants in inorganic
form. Determinations of organic sulfur from the residue of 30-
day-old plants were made and indicate a reciprocal relation to the
inorganic sulfur content.

YIELD AND INORGANIC SULFATE CONTENT AS AFFECTED BY
SULFATE CONCENTRATION?

Table 8

In table 8 are presented the yield and the hot water extractable
sulfate from alfalfa plants grown in solutions with definite concen-
trations of sulfate, maintained by renewing the solution every three
days. The yield of dry matter in plant tops was increased by supply-
ing sulfur up to 8 to 16 parts per million as sulfate in the solution.
During the earliest part of the experiment 16 parts per million of
sulfur seemed to give better growth than 8 parts per million. Later
in the experiment the lower concentration appeared to be fairly
adequate. Sulfate determinations indicated that some ex-osmosis of
sulfate occurred for higher concentrations the last 10 days of the
trial. With these plants there was further evidence of some stimula-
tion about the least optimum concentration, as shown graphically in
figure 13.

The sulfate extractable in hot water increased rapidly up to the
least concentration necessary for optimum growth. A greater supply
of inorganic, or hot water extractable sulfate, was found in the plants
at 30 days of age than at earlier or later growth periods. It appears
that as fast as the plants gain some capacity a considerable amount

1927] Powers: Studies of Sulfur in Relation to the Soil Soluti

157

158 University of California Publications in Agricultural Sciences [Vol. 5

/*/,///$ ram i o f \St*/f> n *r

Fig. 12. Graph showing yield from limited amounts of sulfur.

E FFECT OF SULPHATE CONCENTAT/ON ON THE YIELD OF ALFALFA

FOX 30 DA Y PER tOP

Fm /3

.2 O

'S

?__/.<?

Concentration ofSO^ , parts per m////ori.

Fig. 13. Grapli showing yield from culture solutions maintained with different
concentrations of sulfur.

1927]

Powers: Studies of Sulfur in B elation to the Soil Solution

159

of sulfate is taken in, and later this sulfate is assimilated. Plants
grown in the plant house at the University of California were
benefited rather than injured by removing them from a complete
solution after the first six weeks to a solution lacking sulfate, and they
appeared to have sufficient sulfate to carry them up to the blooming
period.

TABLE 8

Effect of Sulfate Concentration of Culture Solution on Yield and Sulfate
Content of Alfalfa at Different Stages of Growth

Sulfur p. p.m. in

Mean yield in grams dry plant tops

Plant sulfate extractable with
hot water, per cent

culture solution
(added as CaSCW

Growth period — days

Age of plants—

days

10

20

30

40

10 and 20

30

40

None

01 ±001

02± 002

. 05± 006

09±002

000

.150

.074

2

Oli.OOl

03± 002

07± 003

23± 006

.068

652

291

4

02± 001

04± 002

23± 005

.63±

.217

750

.285

8

02± 000

09± 005

37± 007

79± 016

440

.886

255

16

02± 000

07± 003

28± 005

85±027

506

1 165

.259

32

02± 001

09±004

28±007

79±018

.386

896

350

64

02±001

10± 005

27± Oil

76± 021

.929

.975

.448

Complete solution

02± 004

04± 002

14± 003

43± 012

.979

1 410

317

From these studies it appears that 8 to 16 parts per million of
sulfur or 24 to 48 parts per million expressed as sulfate, depending
on age, is sufficient for best growth of alfalfa for these conditions.
The sulfate contents of displaced soil solutions from a half-dozen
representative Oregon soils (that have been included in sulfur experi-
ments seven to ten years both with and without sulfur) reported
above, throw further light on this problem.

SULFATE CONCENTRATION EXPERIMENT WITH SOLID CULTURE

MEDIUM

A parallel experiment was conducted in pots of quartz sand to
note the effect of a solid medium on concentration and diffusion.
Duplicate one-gallon jars of washed Ottawa silica sand were arranged
so that, with the aid of an aspirator, solutions could be removed for
renewal. Five alfalfa plants were grown in each jar. The yield was
not increased with solutions containing more than 8 parts per million
of sulfur. It is possible that transpiration changed the concentration
of sulfate during the 3-day intervals between solution changes,
although a little free liquid was present in the bottom of each jar.

160 University of California Publications in Agricultural Sciences [Vol.5

There may have been a concentration of sulfate at the surfaces of the
quartz grains.

The rate of diffusion of sulfate ion may be expected to vary with
a number of factors and a study is under way in quartz flour and
quartz sand.

Two lots of quartz flour and two of quartz sand moistened to the
moisture equivalent point were placed in trays 25 x 25 x 60 cm. The
two sides, one moistened with .01 N KC1, the other with .01 N H2S04,
were brought into contact and kept air tight at uniform temperature.
In 45 days quantitative determinations of 1 :1 extracts showed that
sulfate had diffused 4 to 6 cm. in the quartz flour and 8-10 cm. in the
sand. After 90 days a second test showed that diffusion had pro-
ceeded at a uniform rate. Apparently roots go to the nutrient more
than nutrient goes to the roots. Concentration due to transpiration
and surfaces may tend to compensate for slower diffusion in solid
medium than in solution cultures. Results indicate that a suitable
sulfate concentration in medium sand is not greatly different from
that needed in water cultures.

KEACTION STUDIES

The reaction of the solutions used in the water culture studies
above described was corrected almost daily where necessary, to keep
it between pH 5.5 and 6.0, which appears to be most favorable for
alfalfa in solution cultures. At or above pH 6.5 a lighter green color
developed in tops and a brown color on roots. Below pH 4.8 roots
became dull in appearance and growth was retarded.

One culture series, table 5, c, was set with barley seedlings to
compare the rate of change in reaction in a single salt solution of
ammonium sulfate with grain to that induced by alfalfa. The reaction
became unfavorably acid with grain in about half the time required
with alfalfa. Alfalfa removes sulfate from solution at about the
same rate as ammonium ion and affords less opportunity for the
sulfate radicle to accumulate in the solution and, by combination with
water, to increase the concentration of hydrogen-ions.

To learn more definitely the reaction best suited to inoculated
alfalfa, water culture solutions were prepared containing only 20
parts per million nitrogen and with different pH values.* Eight

* This experiment was conducted in cooperation with Mr. Charles Hartmann,
Jr., former Assistant in Soils, Oregon Agricultural Experiment Station.

1927] Powers: Studies of Sulfur in Relation to the Soil Solution 1(51

stoneware jars, each of 4-gallon capacity, were provided with covers
so as to support 25 plants per jar and Avere filled with nutrient
solutions. Two jars were filled with "complete" nutrient solutions
and adjusted to a pH value of 5.8. The other solutions were of similar
salt proportions except that little nitrate was present. The reaction
was stabilized by addition of potassium acid thalate in all cases
equivalent to 200 parts per million. Two jars were made up to
pH 5.2, a second pair to pH 6.0, and a third pair to pH 7.2. A fair
growth was obtained in all but the alkaline solutions. The average
yield for controls for 2 months' growth was .35 gram tops per plant.
Cultures maintained at pH 7.2 yielded .13 gram of tops, and those
kept at pH 5.2 yielded .21 gram tops per plant.

The greatest development of nodules occurred on roots of plants
grown at pll 6.0. Nodules developed in the control the last week of
the experiment. The range of pH in which alfalfa can grow appears
to be about pH 4.8 to 7.0 and to be wider than for alfalfa bacteria,
which will not tolerate such an acid solution as will alfalfa. Alfalfa
appears to do best in a slightly acid culture medium. The equipment
used and the comparative growth in different solutions after 5 weeks
is shown in figure 11.

DISCUSSION

Is Sulfate Concentration in Soil Solutions Sometimes
Too Low for Best Growth?

A study of gains and losses of soil sulfur, its oxidation, and the
seasonal sulfate concentration in the soil solution, strongly indicates
that certain soils at times have an unfavorably low supply of this
nutrient. Sulfate concentration in the soil solution is apparently
more closely related to the sulfofying power of a soil than to its total
sulfur content. Many northwestern soils, however, with only 150 to
400 pounds total sulfur in the plowed surface of an acre, respond to
sulfur applications, while relatively few having more than 500 or
600 pounds of sulfur in 2,000,000 of surface soil give much response
in the way of increased yield from sulfur applications. In the
1916 series of Reimer plats on Antelope clay adobe, near Medford,
any sulfur-bearing fertilizer has strikingly increased alfalfa yields.
Sulfur-free fertilizers supplying soluble phosphates, potassium, or
nitrates have not materially increased yields. Moreover, calcium com-

162 University of California Publications in Agricultural Sciences [Vol.5

pounds in these trials have not caused larger crops.50 These facts
led to the view that many basaltic soils in the northwest were in need
of sulfur per se. Studies herein reported have developed good evi-
dence that unfavorably low concentrations of sulfate are less general
than formerly supposed, yet they may be found at times in certain
soils.

Reviewing the evidence here presented, it is noted that certain
soil solutions were found which in certain cases yielded but 14 and
16 parts per million of sulfate. For a given set of conditions, the
crop-producing efficiency of a limited amount of sulfur decreases
below a certain minimum. Sulfur in alfalfa seed seems to be insuf-
ficient to develop properly and to mature alfalfa plants. Further,
the least optimum concentration of sulfate for alfalfa appears to
range from 48 to '24 parts per million during the early weeks of the
growth period. The maximum demand and perhaps the whole need
of sulfate, moreover, is met during these early weeks of the growth
cycle, when sulfur oxidation on certain soils has been slow and sulfates
in the soil may have been depleted by leaching in the wet season.
Diffusion in medium-textured soils may be much slower than in water
culture solutions. Numerous factors will affect the concentration
needed, as pointed out by Hoagland and Martin.-'7 Johnson's work31
seemed to indicate that reaction may affect sulfate absorption by plants
from solution of low sulfate concentration ; also, that acid or humid
soil may supply sulfate needed from a lower concentration than that
in neutral soils, and that sulfate production in soil is increased by
cropping. Diffusion will vary with temperature, surface tension,
texture, and moisture content. Sulfate additions to certain soil solu-
tions and lysimeter waters"''' used as culture media for alfalfa and
grain seedlings have increased the growth of these plants.

The majority of soils studied which respond to sulfur applications
with alfalfa have 100 parts per million or more of sulfate, and other
reasons for the marked increases in yields secured from this treatment
must be found.

Does Sulfur Serve to Hold Calcium and Other Bases in Solution?

It has been noted in lysimeter studies at different experiment
stations that there is a mutual effect of calcium and of sulfate on the
composition of the percolate. Supplying either of these ions tends
to increase the amount of the other found in a given amount of
percolate from lysimeters.59

1927] Powers: Studies of Sulfur in Relation to the Soil Solution 163

The most striking and general effect of sulfur on the soil solution
encountered in these experiments is the increase in concentration of
calcium, following application of sulfur or sulfate. This has been
true not only for fallowed pot experiments but for samples from
sulfured and unsulfured field soils. In certain cases, as with
Deschutes sandy loam, potassium concentration in the soil solution
was greatly increased following sulfur treatment. Increase in mag-
nesium in the soil solution is also noticeable following sulfur applica-
tion. The calcium in solution is frequently doubled or trebled as a
result of sulfur application.

Water culture experiments show that where sulfates of calcium,
potassium, or magnesium are supplied to alfalfa plants in partial
nutrient solutions, 2 days in 6, calcium sulfate is the most favorable
form and results in the largest amount of growth. Inversely, when
calcium is supplied in partial solutions as sulfate, nitrate, or phos-
phate, the calcium sulfate is a very favorable source of calcium.

The amount of readily soluble and of replaceable calcium and other
bases present in a soil, as indicated by Kelley,33 is closely related to
the composition of the soil solution. Madera sand, after 6 or 12 weeks
of incubation with sulfur, was found to have released large amounts
of calcium to the liquid phase. The replaceable calcium in this soil
is low and some carbonates probably were dissolved. A year later
the amoxint of calcium in solution had greatly decreased and the
potassium in solution had markedly increased. Either there had been
a slow solubility effect on relatively insoluble potassium-bearing com-
pounds in the solid phase, or, what is more probable, the calcium ion
brought into solution from carbonates had participated in a base
exchange with the base-absorbing complex of the soil.

An important function of sulfur or other anions, as pointed out
recently by Burd,8 appears to be that of holding cations in solution
and thus maintaining a favorable concentration of nutrients in the
soil solution. He has suggested that when nitrate is largely removed
by growing crops the sulfate operates to perform this function and
to keep bases in available form. A 4-ton crop of alfalfa requires about
300 pounds of calcium.32 The concentration of calcium ion in the
soil solution for some of the soil types studied has been found to be
as low as 20 or 30 parts per million at certain times. At present it
appears that one of the leading effects of sulfur is to bring calcium
and other bases into the soil solution and to hold them there.

1(U University of California Publications in Agricultural Sciences [Vol.5

Will the Average Application of Sulfur Hasten Soil Deterioration?

Recent studies by Gedroiz17 and others indicate that the replace-
able bases adsorbed by the soil-adsorbing complex of a fertile soil
should be mainly calcium or the bivalent bases, calcium and mag-
nesium. Further, that when this adsorbing complex becomes unsatur-
ated with bases, as in aged acid soils, and contains much adsorbed
hydrogen ion instead, these complex silicates may tend to become
unstable and to deteriorate into the simpler oxides, namely, iron,
silica, and aluminum oxides. The result may be a denser structure
and a loss of base-adsorbing capacity. Perhaps a similar condition
may come about with a soil impoverished of replaceable calcium in
the case of a sodium-saturated, adsorbing complex with a "black
alkali" condition, which may be a possible cause of "slick spots." It
is conceivable that heavy and continued applications of sulfur may
hasten removal of calcium ion and ultimately lead to soil deterioration,
especially under conditions favorable for leaching. After an initial
application, subsequent sulfur treatments are often effective if applied
at a lighter rate. Where fertilized alfalfa is consumed on the farm
and over-irrigation is avoided, the increase in organic matter caused
by moderate applications (that is, 80 to 100 pounds an acre) of sulfur
every 3 or 4 years may have little effect on soil deterioration. It
would seem that the use of sulfur as a fertilizer may be more safely
practiced on basaltic soils that are liberally supplied with different
forms of calcium.

Does Sulfur Improve Reaction of Arid Soils for Alfalfa?

Nitrate is known to be taken into the plant better under slightly
acid conditions, and sulfur may improve reaction for nitrate adsorp-
tion by alfalfa. Johnston seems to find31 that sulfate is taken up
by alfalfa best when the pH value of the culture medium is about 5.8.
Iron and phosphate are known to be relatively insoluble under alkaline
conditions. Sulfur tends to increase the solubility of these nutrients
up to a point where the calcium dissolved begins to react and cause
reprecipitation. Sulfur doubled the amount of iron in solution in
Antelope clay adobe. Ferric chloride applied by spraying on young
growth on this soil resulted in the same improvement in color and
yield that has been characteristic of sulfur-treated plats.

In nutrient solutions correction of reaction by addition of dilute
sulfuric acid secured larger growth and better color of alfalfa than
resulted from addition of hydrochloric acid. This sulfate may have

1927] Powers: Studies of Sulfur in B elation to the Soil Solution 165

affected the form of iron in the culture solution or it may have acted
directly. Possibly the chlorine in the small amount added was in-
jurious. Alfalfa grows best in a slightly acid medium, as indicated
by Theron07 and confirmed herein. The best reaction for the alfalfa-
radicicola combination was found to be about pH 6.0.

Sulfur has been found effective in improving the reaction and
structure of alkali soil at Kearney Park Experiment Field, Califor-
nia, and at Vale Experiment Field in Eastern Oregon.30 Sulfur
application may result in improved permeability in alkali land, and,
by improvement in soil structure or possibly by modification of surface
tension, may render soil more drought-resistant.

There are numerous other effects of sulfur on physical, chemical,
and biological conditions related to plant nutrition. The three factors
discussed above have stood out as being of chief importance in these
studies with the soil solution. Which of these effects will be of major
importance may depend on the particular soil and conditions at hand.

SUMMARY

1. Sulfur and sulfates applied to Madera sand soil in pot tests
caused marked increase in calcium ion and a definite increase in other
bases in the displaced soil solution. Calcium and sulfate ions go into
the alfalfa plant especially well together.

2. Heavy applications of sulfur resulted in increased soil acidity,
which caused an increase in phosphate and iron content of the soil
solution up to a certain point, after which bases dissolved or replaced
tended to precipitate these two ions from the soil solution.

3. Heavy application of sulfur tended to inhibit nitrification,
though the normal application, or 100 pounds per acre, on arid soils
may increase growth and nitrogen in the soil.

4. Evidence was found of base exchange as sulfur oxidation in-
creased the concentration of hydrogen ion and then of other cations.
Fixation and exchange of bases applied in sulfates, as in potassium
sulfate, was noted.

5. Analyses of displaced soil solutions of several sulfured and
unsulfured soils from fertilizer experiment fields tend to confirm
results secured with Madera sand and further indicate that the
sulfate content of some soils at certain seasons is very low. Further,
that the effect of sulfur will depend much upon the particular soil
at hand.

166 University of California Publications in Agricultural Sciences^ [Vol.5

6. Sulfur is needed most by alfalfa during the early weeks of the
growth period. Sulfur applications increase sulfofication and the
sulfate content of the soil solution, and they may in turn serve to
bring bases into solution, resulting in a more concentrated soil solution
and decreased transpiration.

7. Water culture experiments indicate that a concentration of 48
to 24 parts per million of sulfate is most favorable for the growth of
alfalfa under the conditions of the trial. The maximum production
secured per milligram of sulfur was .18 gm. alfalfa and was produced
with a solution having an initial sulfate content of 15 parts per
million.

8. An average application of sulfur appears to improve the reaction
of arid soils for alfalfa nutrition, resulting in increased growth and
higher chlorophyll and sulfate content.

9. It is concluded (a) that some soils may have a sulfate content
which is unfavorably low for best growth of alfalfa, especially early
in the growth period; (b) that sulfur oxidizes to sulfate and brings
additional calcium and other bases into solution; (c) that sulfur in
moderate amounts improves the reaction of arid soils for alfalfa
nutrition; (d) that the sulfur applications which are of greatest
benefit will depend on the soil at hand; and (e) that ordinary appli-
cations of sulfur for alfalfa on the arid basaltic soils or soils liberally
supplied with calcium compounds is probably good practice, especially
where the growth secured is consumed on the farm.

19271 Powers: Studies of Svlfur in Bclation to the Soil Solution 167

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2 Ames, J. W., and Richmond, T. E.

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s Ames, J. E., and Boltz, G. E.

1916. Sulfur in relation to soils and crops. Ohio Agr. Exp. Sta. Bui., vol.

292, pp. 219-56.
* Boullanger, E., and Dugardin, M.

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s Brown, P. E., and Gwin, A. B.

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i Brown, P. E., and Kellogg, E. H.

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20 Hall, E. H.

1922. Sulfur and nitrogen content of alfalfa grown under various condi-

tions. Bot. Gaz., vol. 73, pp. 401-11.
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-- Hart, E. B., and Tottingham, W. E.

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24 Harris, J. A., et al.

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25 Hibbard, P. L.

1924. Methods of analysis (mimeographed), pp. 72-78.

26 Hibbard, P. L.

1921. Sulfur for neutralizing alkali soil. Soil Sei., vol. 11, pp. 385-87.

27 Hoagland, D. R., and Martin, J. C.

1923. A comparison of sand and solution cultures with soils as media for

plant growth. Soil Sei., vol. 16, pp. 367-88.

28 Hoagland, D. R.

1919. Relation of concentration and reaction of the nutrient medium to the
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29 Joffe, J. S.

1922. Acid phosphate production by the Lipman process. Soil Sei., vol. 14,

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so Johnston, W. W., and Powers, W. L.

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3i Johnston, W. W.

Studies of rate of sulfate formation and intake by plants. Manu-
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59 Unpublished data, Oregon Agr. Exp. Sta.