LIBRARY,
‘A 8c M COLLEGE.
CAMPUS.

R79-437-6m

TEXAS AGRICULTURAL EXPERIMENT STATION

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

BULLETIN NO. 545 JUNE, 1937

DIVISION OF PLANT PATHOLOGY AND PHYSIOLOGY
AND
DIVISION OF CHEMISTRY

g1 B Fzxxmge “g “n8
a °“‘
k!t\eu\\\\"‘c¢\\naa Staﬁmn. T2115-

RELATION OF SOIL ACIDITY
TO COTTON ROOT ROT

 

AGRICULTURAL AND MECHANICAL COLLEGE OF TEXAS
T. 0. “FALTON, President

Cotton plants grown in containers of soils Varying naturally in
hydrogen-ion concentration (a measure of soil acidity) were inocu-
lated with cotton root rot. Incidence of root rot following inocula-
tion, later spread of the disease, and overwint-ering to following
years, were all greater in the more alkaline soils and less i11 the
more acid soils.

Soil materials were adjusted artiﬁcially toward acidity by addi-
tions of sulphur, sulphuric acid, calcium sulphate, or ammonium
sulphate, or toward alkalinity by additions of lin1e or sodium car-
bonate. I11 general, the soils made acid were found to be unfavor-
able, and the soils made alkaline were found to be favorable, for
the disease. The hydrogen-ion concentration of the surface soil
seemed of particular importance. A six to twelve-inch surface layer
of acid soil caused immediate or ﬁnal disappearance of root rot,
while acidiﬁcation of the deeper soil, with the surface layer left
alkaline, did not eradicate the disease.

Sulphur mixed into soil in ﬁeld plats reduced the percentage
of root rot on cotton plants but did not eradicate it. Sulphur
applied in the surface soil ﬁnally made the soil acid to depths of
more than two feet. The acidity or alkalinity of the surface
soil apparently was of special importance i11 these experiments also.
It is impracticable to acidify calcareous soils, and application of
soil acidiﬁcation for control of root rot in other soils is still in
the experimental stage. .

The experiments summarized in this Bulletin have shown that
soils originally acid or made acid by additions of various chemicals
are less suitable for infection of plants by the root-rot fungus, and
less suitable for continued survival of the fungus from year to
year, than are soils originally neutral to alkaline or made so by
chemical additions. Unsuitability of acid soils to the root-rot
fungus is not necessarily’ due directly to the hydrogen-ion con-
centration, but is associated closely with this factor.

CONTENTS

Introduction _

Distribution of Phymatotrichum root rot in Texas as related t0 differ-

ences in soil acidity_

Experiments on the general relation of soil reaction to prevalence and

destructiveness of root rote _ _

Comparison of soils of naturally differing acidity ________________ _-

Preliminary experiment with Lufkin ﬁne sandy 10am soil

adjusted by various additions --

Lufkin ﬁne sandy loam soil adjusted to different hydrogen

ion concentrations with lime, sulphur, and sulphuric

acid .... __ r1

Experiment with four soil types with the reaction adjusted

by various additions“

Lufkin ﬁne sandy loam soil acidiﬁed at various depths and

with inoculum at various depths __________________________________ __
Experiments with soil acidiﬁcation as a possible means of control---

Preliminary test of plain and oxidied sulphurs in small

containers

Sulphur applied at various depths in small plats __________________ __
Sulphur applied at small rates to surface soil, in plats in

which root rot was well established ________________________________ __

Discussion

Summary

Literature cited“-

10

13

25

27
29

34

BULLETIN NO. 545 JUNE, 1937

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT
By J. J. Taubenhaus, Chief, and W. N. Ezekiel, Plant Pathologist,
Division of Plant Pathology and Physiology; and J. F.
Fudge, Assistant Chemist, Division of Chemistryi‘

The root-rot disease, caused by the fungus Phymatotrichum omnivorum
(Shear) Duggar, attacks a large proportion of the different kinds of
cultivated plants, causing enormous losses not only of ﬁeld crops grown
in Texas and elsewhere in the Southwest but also of orchard trees,
ornamental shrubs, and shade trees. For several years, studies have
been made on the possible relation of the acid or basic reaction of the
soil to Phymatotrichum root rot. Some results of these studies have
been published (14, 5). It is the purpose of this Bulletin to present, in
brief form, the results of a number of experiments, and to summarize our
present knowledge of this important factor as it affects the distribution
and prevalence of root rot.

DISTRIBUTION OF PHYDIATOTBICHUBI ROOT ROT IN TEXAS AS
RELATED TO DIFFERENCES IN SOIL ACIDITY

Root rot is much more prevalent in the heavier soils of Central,
South, and Western Texas and is less common in the generally lighter
soils of East Texas (4). In 1925 and 1926, a survey was made of a
number of cotton ﬁelds, and composite samples of the upper three
inches of soil were taken from each ﬁeld (17). Root rot was found
throughout the range of soils included in this survey—~in one of the most
(acid ﬁelds, of pH 5.5, and in the most alkaline, of pH 8.6. However, the
percentage of ﬁelds with root rot in the neutral to alkaline soils (pH 6.5
to 8.6) was twice that in the acid soils (pH 5.5 to 6.4). Considering the
severity rather than merely the presence or absence of root rot, a marked
relation of pH to root rot was evident. While the disease was present in
a ﬁeld of which the surface soil had a pH of 5.5, there was only a trace
of the disease in this ﬁeld. In ﬁve cases of root rot on soils of pH 5.9,
three were only traces. All ﬁve ﬁelds with root rot at pH 6.0 had only
a trace of the disease. All ﬁve cases from pH 6.1 to 6.3 were recorded
as traces. It was only with soil of pH o-f 6.5 or higher that the disease was
found in destructive abundance. In 10 ﬁelds with root rot, selected at
random from those between pH 7.1 and 7.9, only two were recorded as
having less than 1 per cent of root rot, ﬁve had between 10 and 20
per cent, and the other three had from 20 to 70 per cent.

Root rot was thus not only of more frequent occurrence on soils of
pH 7.0 to 8.0 than on soils of pH 5.5 to 6.5, but also it was more often
of destructive abundance when present on neutral to alkaline soils than
when present on acid soils.

Dawson and Collins (3) have reported similarly that heavily infested
areas are calcareous and alkaline (pH 7-8.3), while root rot is less
prevalent or absent in non-calcareous soil of neutral or slightly acid

*The Writers are indebted to Mr. W. T. Carter for identiﬁcation of the
soil types; to Dr. G. S. Fraps for advice in planning experiments and
supervision of the chemical work; and to Mr. E. C. Carlyle for chemical
work during 1927-1929. ‘

6 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

reaction (down to pH 6.0). In later studies (1) it was concluded e_

that while there was this general correlation of prevalence of root rot

with pH and calcium carbonate content of the soil, this did not apply 
within a given soil type of Texas Blackland soils. This was presumably -e
because such soils are almostuniformly favorable for root rot insofar 

as determined by the soil reaction.

EXPERIMENTS ON THE GENERAL RELATION OF SOIL REACTION 

TO PREVALENCE AND DESTRUCTIVENESS OF ROOT BOT

The results of the ﬁeld survey indicated that Phymatotrichum root rot i
is relatively less destructive in somewhat acid soils than in alkaline
soils. It was still necessary t0 determine Whether this was due actually 
to differences in the soils, or whether it might not have resulted from 
climatic 0r regional inﬂuences. In order to study this, a variety of experi- -

ments has been carried out under partially controlled conditions,
usually in containers of various sorts exposed to natural weather con-
ditions. Soils naturally varying in acidity have been transported to
College Station and installed side by side in containers. In other experi-
ments, soils have been adjusted toward acidity or alkalinity as desired.
In attempts to determine the ions involved in the relation, soils have
been made acid with sulphur, sulphuric acid, calcium sulphate, and
ammonium sulphate, or made alkaline with lime or sodium carbonate. In
some of the experiments the depth to which soil has been acidiﬁed has
been made a variable.

Comparison of Soils of Naturally Diﬁering Acidity

In this experiment, soil material of seven different types was trans-
ported to College Station and placed in long wooden boxes, 12 feet
long, 2 feet wide, and 3 feet deep. Each soil was dug to a depth of three
feet. Each six-inch layer was sacked separately, and each layer replaced
at its original depth in the boxes. Cotton was planted in a row along
the middle of each box from 1928 through 1932. During 1928 root rot
was introduced at one end of each box, by repeated artiﬁcial inoculation
with naturally-infected cotton roofs (13).

Results for this experiment are given in Table 1. The best relation
of root rot to the soil reaction appeared in the initial spread of root rot,
following inoculation in 1928. Spread was successively greater with soils
of higher pH values. Only one of the inoculated plants succumbed in the
Susquehanna soil with pH 5.5, and not one plant in the Tabor soil with

pH 5.8, while most of the plants succumbed in the two boxes of more l

alkaline soils.

In 1929, root rot reappeared in each box in which it had caused any
infection the preceding year, and attacked a higher percentage of plantsffi

than in 1928. However, a large amount of inoculum added to each box

in October, 1928, furnished additional material for possible overwinter-i“
ing. {The ability of root rot to survive in these various soils was shown
better by the results during the next three years, when its reappearancef

depended solely on successful overwintering.

 

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT 7

With the cessation of inoculation, root rot disappeared from the acid
Susquehanna ﬁne sandy loam, and did not appear again during the period
of the experiment. No root rot was found at any time in the shallow
phase of Tabor ﬁne sandy loam, which became as acid as the Susque-
hanna soil. The Ochlockonee clay 10am, which varied from pH 6.3 to
5.9, supported root rot for only three years, and none occurred after
1930. In the next three soils, varying from about neutrality to slight
alkalinity, root rot survived for the period of the experiment.

Special explanation seems necessary for the results in the Houston
black clay. This soil was consistently the most’ alkaline one in the
experiment, and it is a type on which root rot is highly destructive in
the ﬁeld. Yet after causing complete loss in this box in 1929, and 93% loss
in 1930, root rot did not show up in 1931 and 1932. This is to be inter-
preted not as resulting from unsuitability of the soil for the fungus,
but rather from the fact that the Houston soil was “too favorable” for
the fungus, and caused a natural periodicity of root rot such as occurs
also under ﬁeld conditions with soils of the Houston series. As the

~ writers have discussed previously (14), the periodic cumulative increases

of root rot in such highly favorable soils, usually followed then by abrupt
decreases for several years, may be explained as follows: When many
plants become infected and the roots decay early in the season, with result-

Table 1. Spread and survival of root rot 0n cotton plants growing‘ in soils
differing naturally in acidity.

I
pH of soil, Spread of Total percentages of
1 Sourtie of 0-2 feet deep lroot rot ‘ plants infected
Soi type soi s, __________ a ong rows
county during 1928, | l
1928 1929 1931 feet 1928‘1929I193O 1931 1932
Susquehanna ﬁne sandy loam, I
shallow phase . . . . . . . . . . . .. Brazos. . . .. 5.5 5.6 5.2 0 2 8 0 0 0
Tabor ﬁne sandy loam, |
O shallow phase. .1 . . . . . . . . . . . R.obertson. . s.s| 5.7 5.2 0 0 50, 0 0 0
chlockonee clay 0am. . . . i. . Brazos. . . .. 6.31 5.9 6.3 4 27 9 20 O 0
Tabor {goo sandy lloam . . . . . .. Brazos. . . .. 6.71 1.0 7.; 4V 29 s4’ o 2o its)
Kirvin ne sandy oam . . . . . .. Brazos. . . .. 7.1 7.1 7. 5 30 8O 44 32
Caddo ﬁne sandy loam . . . . . .. Robertson. . 7.6; 7.5 7.8 7% S3 82 31 16 19
Houston black clay . . . . . . . . .. Bell . . . . . . . 7.7‘ 7.6‘ 8.1 7% 74 100 93 0 0

   

ant death of the vegetative strands on these roots, there are relatively few
undecayed portions of roots left on which the fungus can overwinter in a
vegetative condition.

Such asequence of events apparently took place in the ‘box of Houston
soil in this experiment. Root rot attacked 93% 0f the plants by the time
notes were taken in the fall of 1930, and presumably “ate itself out” on
the few remaining roots before the following season. Under ﬁeld condi-
tions, root rot would not be entirely eliminated, but it is possible that
in the small portion of soil present in the box there happened to be
neither living vegetative material nor living sclerotia at this time to
carry the fungus along. It is, of course, possible that the fungus may
have been present in a dormant condition and merely have failed to cause
infection during 1931 and 1932.

8 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

Taken together, the results of this experiment showed a close relation
of pH of the soil with extent of spread of root rot in the boxes, and close
relation also of pH to the percentage of original incidence of root rot
following inoculation and to the overwintering (with the exception of
the Houston soil as explained above). As in other experiments, foot rot
could be started even in the more acid soils, but did not survive for many
years, even in the marginal Ochlockonee soil.

Preliminary Experiment with Lufkin Fine Sandy Loam Soil Adjusted
by Various Additions

An experiment was set up in 1927 in a series of 120 earthenware
cylinders (drain tiles), each 2 feet deep and 18 inches in diameter. These
were sunk upright in the ground, nearly to the ground level, and ﬁlled
With Lufkin ﬁne sandy loam soil material. Various materials speciﬁed in
Table 2 were worked into the surface soil t0 a depth of four to six
inches. These applications were made partly in 1927 and partly early in
the spring of 1928, but the entire amounts had been applied before
cotton was planted in 1928. Six cylinders were used for each set of
treatments. The cotton was thinned to ﬁve plants per cylinder, making
the total about 3O plants for each of the series. The plants were inocu-
lated artiﬁcially with Phymatotrichum root rot in 1928 and again in
1929, by the method previously described (13).

It will be noted from table 2 that the pH of the soil in some of the
series changed greatly in response to the treatments. This shift from
neutrality was generally greater in 1928 than in 1929. In 1928, the
changes Were conﬁned largely to the surface layer (about 0-8 inches) of
the soil. By the end of the second year, the pH was approximately uni-
form in most of the cylinders to about 12 inches deep; the soil at 12 to
18 inches was usually intermediate between the pH of‘ the upper foot
and the original value; and the soil at 18-24 inches had often shifted
slightly from neutrality. That is, during the second year the changes due
to the treatments were less intense, but extended to greater depths.

The results are summarized by individual series in Table 2. It is to
be noted that root rot was introduced successfully and killed some of
the plants in all series except the one in which the extreme acidity killed
all the cotton plants. A general relation of the soil acidity or alkalinity to
the incidence and destructiveness of root rot is evident. Additions of
pure calcium carbonate, hydrated lime, or sodium carbonate made the
soil alkaline and were in general favorable to root rot. Additions of
ammonium sulphate produced little change in pH and no deﬁnite
changes in root rot as compared with the check. Sulphuric acid, powdered
sulphur, and soda alum made the soil more acid, and reduced the inci-
dence of root rot. Root rot overwintered in some of the containers of
each series in the winters of‘ 1927 and 1928, appearing on plants of the
succeeding crop prior to the inoculation.

The correlation is more evident in Table 3, in which the different
series are grouped by the pH of the soil without regard to the different

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT

9

treatments. The differences in pH were associated more signiﬁcantly with
changes in the mortality from root rot than in the incidence of the

disease.
Table 2. Effect 0f surface applications of various materials to Lufkin ﬁne
sandy loam soil material 0n incidence of root rot.
Plants attacked Plants killed
Mean pH, by root rot, * by root rot,
Treatments. 0-6 inches percentages percentages
pounds per acre
1928 1929 1928 1929 1928 1929
i
Calcium carbonate, 32,000 . . . . . . . . . . . . . . 7.8 7.6 67 55 43 39
" " 16,000 . . . , . . . . . . . . . . 7.8 7.5 8O 79 37 79
" ” 4.000 . . . . . . . . . . . . . . 7.7 7.4 97 97 61 81
Sodium carbonate. 3,000, plus calcium
carbonate, 16,000 . . . . . . . . . . . . . . . . . . . . 8.0 7.8 100 85 47 77
Sodium carbonate, 3,000 . . . . . . . . . . . . . . . . 7 .4 7 .0 50 57 33 39
Sodium chloride. 2,000, plus calcium
carbonate, 16,000 . . . . . . . . . . . . . . . . . . . . 7.7 7.5 87 77 S7 54

Hydrated lime, 4,000 . . . . . . . . . . . . . . . . . . . 7.6 7.3 80 86 40 S1

None, check . . . . . . . . . . . . . . . . . . . . . . . . . . 7.0 6.9 73 90 27 69

Dry sheep manure, 10,000 . . . . . . . . . . . . . . 6.9 6. 7 83 31 37 6

" " " 20,000 . . . . . . . . . . . . .. 6.9 6. 7 83 61 30 36

Ammonium sulphate, 400 . . . . . . . . . . . . . . . 6.5 6.7 83 78 40 53

Sulphuric acid, 3,400 . . . . . . . . . . . . . . . . . . 5.4 6.0 100 63 37 43

" " 4,000 . . . . . . . . . . . . . . . . .. 5.0 6.1 77 2S 40 13

" " 5,000 . . . . . . . . . . . . . . . . .. 5 .0 6.1 63 50 30 20
Soda alum, 2,000, plus sulphuric acid,
000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 .0 43 50 10 33
Soda alum, 8,000, plus sulphuric acid,
3.000 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 5 7 61 28 16 22
Sodium sulphate, 2,000, plus sulphuric
acid, 5,000 . . . . . . . . . . . . . . . . . . . . . . . . . . 5.0 6.1 47 53 13 47
Powdered sulphur, 1,000 . . . . . . . . . . . . . . 5.4 5.9 67 49 23 27
" " 2,000 . . . . . . . . . . . . .. 4. 7 5 .8 64 47 23 31
" " 10,000 . . . . . . . . . . . . .. 2.9 3.8 "r   

*Tota1 of plants killed by root rot and of those infected but not yet killed.

TNO plants, all killed by acidity.

Table 3. Rearrangement of results in Table 2, with the series grouped by
mean pH values, without regard t0 the treatments.

1928 Results

1929 Results

Mean pH.
of Number of Percentages Percentages Number of Percentages Percentages
surface soil series in the of plants of plants series in the of plants of plants
soil-reaction attacked by killed by soil-reaction attacked by killed by
group root rot root rot group root rot root rot
7_.0—8.0 . . . . . . 8 79 43 7 77 60

6.0-6.9 . . . . . . 3 83 36 9 56 36

5.0-5.9 . . . . .. 6 66 26 3 41 27

4.5—4.7 . . . . .. 2 63 20 0 .. 

2.9-3.8 . . . . .. 1* .. .. 1*

*No plants, all killed by acidity.

10 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

Most of these cylinders were devoted after 1929 to another experi-
ment, but ﬁve of the more acid series were continued through the seasons
of 1930, 1931, 1932, and 1933, to ﬁnd whether root rot would disappear.
The cotton plants in these cylinders were inoculated again in 1930, but
were not inoculated in 1931, 1932, or 1933. Therefore root rot appeared
during these last years only as a result of overwintering successfully
either in these cylinders or beneath them. As shown in Table 4, the sur-
face layers ofsoil in all except the most acid series had by this time
shifted back to pH 6.0 or beyond. There was a gradual decrease in per-
centages of plants with root rot, but this trend occurred in the series in
which the soil was approaching neutrality as Well as in the one that
was still somewhat acid. The acidity obtained in these cylinders was
evidently insuﬁicient to prevent the incidence of root rot following inocula-
tion, and the acidity prevailing after 1930 in these cylinders evidently
could not prevent the disease from overwintering. The sole exception was
the series treated with the highest rate of sulphur. No cotton plants
could be grown in these cylinders during the early years of the experi-
ment, and the plants that were grown in 1930 and later years did not
succumb to root rot from the inoculations made in 1930.

In this experiment, root rot was deﬁnitely eliminated only in the
one series of cylinders with a soil reaction of pH 4.2-4.4. It survived
in soils adjusted by various treatments to around pH 5, and was favored
by treatments that changed the reaction toward alkalinity.

Incidence and survival of root rot in Lufkin ﬁne sandy 10am soil
nlaterial plus surface applications 0f various materials.
(Cotton plants inoculated 1928, 1929, and 1930; 6 cylinders per series.)

Table 4_.

         

 
 
 

Mean pH of soil, Percentage plants attacked
0-6 inches by root rot
Treatments,
pounds per acre | [
Sept. Mar. Dec. Nov. Jan.
1928 1930 1931 1932 1934 1928 1929 1930 1931 1932 1933
Sodium sulphate, 2,000, plus l i
sulphuric acid, 5,000 . . . . . . . . 6.2 6.1 6.8 6.9 7.6 47 53 42 39 7 13

Sulphuric acid, 5,000 . . . . . . . . . . 5.9 6.1 6.6 6.9 7.5 63 SO 74 33 i 36 47

Sulphur, 1,000 . . . . . . . . . . . . . . .. 5.9 6.0 6.6 6.8 7.4 67 49 S3 25 22 18

Sulphur, 2,000 . . . . . . . . . . . . . . .. 4.8 5.7 6.0 6.3 7.0 64 47 67 49 35 30

Sulphur, 10,000 . . . . . . . . . . . . . .. 3.2 3.8‘ 4.4‘ 5.0 5.5 * * 0 0 0 0

 

*No plants, all killed by acidity.

Lufkin Fine Sandy Loam Soil Adjusted to Diiferent Hydrogen-ion Con-
centrations with Lilne, Sulphur, and Sulphuric Acid

A uniform soil was adjusted to the entire depth of the cylindric
earthenware containers to fairly precise hydrogen-ion concentrations, in
series providing sufficient replication to furnish reasonably large num-
bers of plants at each pH. Lufkin ﬁne sandy loam surface soil material,

from 0-12 inches deep only, was used. This was a brownish-gray ﬁne N
sand, naturally slightly acid, of pH 6.2 to 6.3. The method developed by 9':

Fraps and Carlyle (7) was used to determine the amount of sulphuric

acid needed to adjust this soil to various acidities. Additions were made 

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT

directly on this basis in the sulphuric acid series, and with one and one-
half times the calculated amounts in the sulphur series. Since the soil
used was already slightly acid and only slightly buffered, only small addi-
tions, as indicated in Table 5, were required to develop fairly intense
acidity. The sulphur, sulphuric acid, or limestone were added to Weighed
amounts of soil material (the additions being calculated on the air-dry
soil Weight) and incorporated thoroughly into the soil by mixing in a
large box. The mixed soil was then placed in earthenware cylinders, 2
feet deep and 18 inches in diameter, set upright in the soil so that the
tops were only two to three inches above the surface. Twelve of these

11

Table 5. Changes in pH of soil following additions made in April, 1930,
to the entire depth of Lufkin ﬁne sandy loam soil material in cylinders.
pH obtained (mean of all cylinders,
entire depth)
_ Materials added per 100 pounds pH
Series of air-dry soil desired

' Dec. Dec. Nov. July

1930 1931 1932 1933

a 250cc.,2.83 N. H2504 . . . . . . . . . . . . .. 4.0 4.8 5.0 5.2 5.7

b 200 " " " . . . . . . . . . . . . .. 4.5. 4.9 5.0 5.5 6.3

c 150" " ” . . . . . . . . . . . . .. 5.0 5.4 5.3 5.9 7.0

d 100" ” " . . . . . . . . . . . . .. 5.5 5.8 5.5 5.9 7.0

e None . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 6.0 7.0 6.3 7.0 7.3

f 90.7 gm. ground limestone . . . . . . . . . . 8.5 38.0 8.5 8.6

g 907 " " " . . . . . . . . . .. 8.5 8.0 8.4 8.4
h 17.007 gm. sulphur, velvet sublimed
ﬂowers . . . . . . . . . . . . . . . . . . . . . . . . . .. 4.0 4.4 4.6 5.1 5.4
i 13.608 gm. sulphur, velvet sublimed
ﬂowers . . . . . . . . . . . . . . . . . . . . . . . . . .. 4.5 4.4 .6 5.2 5.
j 10.206 gm. sulphur, velvet sublimed
ﬂowers . . . . . . . . . . . . . . . . . . . . . . . . . .. 5. 4.7 .9 5.6 6.1
k 6.804 gm. sulphur, velvet sublimed
ﬂowers . . . . . . . . . . . . . . . . . . . . . . . . . .. 5.5 5.1 5.3 6.1 6.3
l __._
Table 6. Incidence and persistence of Phymatotrichum root rot on cotton
plants grown in Lufkin ﬁne sandy loam surface soil material
adjusted to the entire depth of the containers
to different pH values.
Percentages plants Percentages plants
Numbers of plants attacked by root rot killed by root-rot
Series
1930 1931 1932 1933* 1930 1931 1932 1933 1930 1931 1932 1937
a 164 116 173 101 8 0 0 0 0 0 0 0
b 201 115 188 75 28 0 0 0 6 O 0 0
c 177 114 183 70 71 4 3 0 21 2 1 0
d 148 108 16S 111 78 16 15 34 44 11 10 27
e 172 111 184 115 81 51 40 16 40 28 24 11
f 203 105 165 82 97 82 72 66 64 61 6O 48
g 199 107 128 76 78 72 61 58 39 52 39 38
h 135 95 145 82 18 0 0 O 8 0 0 0
i 197 93 134 62 28 0 0 0 12 0 0 0
j 190 91 140 77 41 2 O 12 24 2 0 12
k 220 93 128 85 46 26 16 7 32 19 9 7

*In 1933, only 6 of the 12 cylinders of each series were available for this experiment.

‘18-24 inches deep, pH 5.5.

12 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

cylinders were used for each of the eleven series of soil treatments.
As indicated in detail in Table 5, the treatments were planned to provide
the following: 4 series treated with sulphuric acid t0 obtain various
acidities; a similar set of 4 series treated with sulphur planned to reach
the same range of acidities; an untreated series; and two series in which
were incorporated respectively 0.2% and 2% of ﬁnely ground limestone,
to obtain deﬁnitely alkaline and calcareous soils to compare with the
acidiﬁed soils.

Periodic pH determinations were made on soil samples taken by 6-inch
depths to the bottoms of the containers. At ﬁrst the pH was fairly uni-
form at all depths. By the end of three years, however, the deeper samples
averaged usually about 0.5 pH more acid than the 0-6 inch samples.
Thus in series a samples from 0-6 inches deep averaged pH 6.1; from
6-12 inches deep, pH 5.8; from 12-18 inches deep, pH 5.5; and from
Differences between the replicate containers
were usually less than 0.5 pH. The values given in Table 5 are averages
for all depths and all containers in the various series. It will be noted
that in both the sulphur and sulphuric acid series the soil was most
acid the ﬁrst year, becoming less acid during the course of the experiment.
The sulphuric acid treatments failed to secure the desired acidities, while
the sulphur additions (made in excess of the theoretical requirements)
produced greater acidity in three of the four series than was desired, but
soon drifted toward neutrality. During the period of the experiment, the
sulphur series maintained greater acidity than the corresponding sul-
phuric acid series.

Cotton was grown in these cylinders from 1930 through 1933. Root
rot was introduced into the containers by copious artiﬁcial inoculation
during the summer of 1930; naturally-infected cotton roots were used
as inoculum (13). No inoculations were made in the succeeding years.
Notes were taken each year on the incidence of root rot, including obser-
vations on the appearance of above-ground symptoms of the disease and
also, at the end of the season, of‘ symptoms on the roots even of those
plants that appeared normal. Exhaustive microscopic study eliminated
certain small plants, particularly in the more acid series, that succumbed
early in the season, usually to damping-off, which was favored by the
soil conditions. These plants were not considered in calculating the
percentages of root rot in the various series (Table 6).

The results in 1930, when the plants in each cylinder were inoculated
with the disease, agreed with previous results in showing the possibility
of introducing root rot even in acid soils by artiﬁcial inoculation. In
the six series of cylinders with soil less acid than pH 5.0, there Was more
than 40% of root-rot infection, while only one of the ﬁve series with soil
more acid than 5.0 had as much as 40% infection. However, Phymato-
trichum root rot resulted from. the inoculation in at leastsome of the
cylinders of every series, even those with soil at pH 4.4, and some of
the plants even in this deﬁnitely acid soil were killed by the disease.

In succeeding years, root-rot infection could occur only as the result
of successful overwintering of the disease. There was a sharp decrease

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT l3

of root-rot infection in the more acid soils. In 1931, the disease did
not reappear in the two more acid of the sulphuric acid series, which
averaged approximately pH 4.8 and 4.9, nor in the two more acid of the
sulphur series, Which averaged pH 4.6. N0 infection with root rot was
found in these series in the following years, although the soil became
less acid.

Meanwhile, the disease diminished progressively in all the series, but
only to a small degree where lime had been added. In 1933, three years
after the original inoculation, more than half of the plants in the limed
series, f and g, showed symptoms of root rot, and more than a third of
the plants were killed by root rot.

There were several intermediate series, in which root rot was still
present after several years, but in which it had decreased greatly in
abundance. This group included series c, with a decrease from 71% to
3% in 1932 and 0 in 1933; d, from 78% down to 34% in 1933; j, from
41% down to 12%; k, from 46% down to 7%; and the check series e, from
81% down to 16%. In these series the soil varied originally from about
neutrality to slight acidity, except j in which the initial pH was 4.7.

Within the period of this experiment, the following occurred: (1)
In the most acid soils, root rot was obtained by the inoculation,
but the percentage was low and the disease could not overwinter in these
soils and did not reappear in following years. (2) In less acid soils,
higher percentages of root rot were obtained by the inoculation in 1930;
there were great decreases in the percentage of infection in the following
year; but the disease had not disappeared completely in three years.
These soils were evidently too acid for favorable overwintering and
seasonal development of root rot. Whether the disease would disappear
completely in such soils in a few additional years is not indicated by
these results. (3) In the calcareous, alkaline soils, still higher initial in-
fections were secured. Only slight progressive decreases in percentages
of root rot occurred in the three following years.

Because of the progressive decrease in soil acidity in these series, it
would be difficult to decide on a limit to the pH that would be expected
to yield the results mentioned for these several groups. The calcareous
soil of pH 8.0 to 8.5 is obviously deﬁnitely in the range favorable for
root rot. Soil more acid than pH 5.0 is probably deﬁnitely unfavorable.
Between about pH 6.0 and pH 7.0, the conditions are apparently unfavor-
able for root rot, but not so unsuitable as to cause rapid disappearance of
the disease.

Experiment with Four Soil Types with the Hydrogen-ion Concentration
Adjusted by Various Additions

In this experiment, four types of soil were employed, each soil material
being used untreated and also with various additions. Some of the
additions were planned to change the acidity, and other additions to
change the plant nutrient content of the soils. The soils were installed in
large boxes, planted to cotton, root rot was introduced by artiﬁcial

l4 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

inoculation, and the effect of the treatments was observed both on
incidence of the disease and on ﬁnal survival under the various condi-
tions. The 63 boxes used for the experiment, each 12 ft. long, 2 ft. wide,
and 3 ft. deep, were set up during the winter of 1928-29. Each box was
put in place by removing the original soil, inserting the box, and then
ﬁlling with the new soil. The soils used are described below:

Tabor ﬁne sandy loam, shallow phase, from an old ﬁeld in
permanent pasture. Surface soil: 0-10 inches, grayish-yellow ﬁne
sand, pH 5.9-6.2. Subsoil: 10-18 inches, yellowish-red clay,
pH 5.8-6.0; 18-25 inches, reddish-yellow to yellow clay, pH 5.6-5.8;
25-32 inches, dense yellow clay, pH 5.8-6.4; 32-36 inches, heavy
yellow clay, pH 6.9-7.4.

Susquehanna ﬁne sandy loam, virgin soil from woods. Sur-
face soil: 0-3% inches, brownish loamy sand, pH 6.5-6.9; sub-
surface, 31/2-10 inches, yellow ﬁne sand, pH 6.1-6.5. Subsoil:
10-16 inches, red clay, pH 5.4-5.9; 16-26 inches, red mottled with
gray clay, pH 5.3-5.7; 26-36 inches, gray clay mottled with red,
pH 5.5-6.0.

Kirvin ﬁne sandy loam, deep phase, virgin soil but heavily
pastured. Surface layer: 0-6 inches, light brown loamy ﬁne
sand, pH 6.8-7.1; 6-12 inches, brownish-yellow ﬁne sand, pH 6.9-7.1;
12-24 inches, yellow ﬁne sand, pH 7.0-7.1. Subsoil: 24-36 inches,
red heavy clay, pH 5.7-6.2.

Lufkin ﬁne sandy loam. Surface layer: 0-12 inches, homo-
geneous brownish-gray ﬁne sand, pH 5.9-6.1. Subsoil: stiff gray
clay, apparently uniform; 12-18 inches, pH 6.0-6.1; 18-24 inches,
pH 5.8-6.1; and 24-36 inches, pH 6.0-6.4.

The soils were dug out in the layers mentioned and sacked, the sacks
were transported to College Station and weighed, and samples were
taken to determine the dry weight of the soil. Additions were made to
these soil materials, in ﬁlling the boxes, on the basis of the weight of
oven-dry soil. The various layers of the soils were placed in their new
locations in the boxes at the same depths as those from which they
had been dug. Additions to the soil materials, unless otherwise speciﬁed,
were made to the entire depth of the boxes. The materials added were
mixed in as the soils were placed in the boxes.

All treatments were made to duplicate boxes. For the Tabor, Susque-
hanna, and Kirvin soils, limestone was used at 1% and 5% of the dry
weight of the soils, and sulphuric acid was added in various amounts
estimated to reach the acidities indicated in Table 7. Soils of certain
other boxes were given special treatments as summarized in Table 8.
The Lufkin soil material was used in another set of boxes (Table 9) in
which the upper soil layers were made acid by addition of sulphuric
acid to reach an estimated pH 5.0, while the deeper layers were made
alkaline by addition of 1% of limestone. The relative depth of these two
layers was the variable. Pairs of boxes were made acid respectively to
6 inches, 12 inches, 18 inches, and 24 inches deep, with the soil below
this depth in each case alkaline. Two other boxes were made acid to the
entire depth, and two were made alkaline to the entire depth.

All the treatments had been completed by May, 1929. Startex variety
(Texas Station No. 7000) cotton was grown in a single row down the
center of each box from this year until 1933. The plants were thinned
usually to distances of about four inches apart, leaving about 36 plants
to the 12-foot row. More plants were left during some seasons, bringing

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT

Table 7. Incidence and persistence 0f Phymatotrichum root rot in boxes of
soil materials, of various soils, adjusted by additions of lime o1-_ of acid.

Average pH of soil,
for 0-2 feet deep

Percentages of plants
attacked by root rot

Soil types and Box
treatments N0.
1929 1930 1931 1932 1933 1929 1930 1931 1932 1933
Tabor ﬁne sandy
loam
checks, untreated. 1 5.7 5.9 5.7 5.9 5.9 51 100 53 31 0
2 6.2 5.8 5.8 6.0 6.1 38 95 38 6 0
1imeadded,1%... 7 7.4 7.3 7.7 7.8 7.9 44 65 74 26 67
8 7.3 7.5 7.9 7.7 8.0 48 97 36 5O 90
” ” 5%... 9 7.7 7.6 7.9 8.1 8.2 38 91 32 0 9
10 7.5 7.5 8.0 8.1 8.2 43 92 33 36 95
acid, to estimated
pH5.5 . . . . . . . .. 15 5.2 5.1 5.1 5.3 5.9 49 78 32 0 0
16 5.3 5.5 5.2 5.6 5.3 24 29 13 0 0
acid, to estimated
pH4.5 . . . . . . .. 17 4.9 5.0 5.0 5.3 5.6 0 9 0 0 0
18 5.1 5.0 5.0 5.4 5.6 8 3 0 0 0
Susquehanna ﬁne
sandy loam
checks, untreated. 19 6.3 6.2 5.7 5.8 6.3 3 7 10 0 0
20 6.1 6.2 5.9 5.7 6.4 3 6 21 0 0
lime added, 1%... 21 7.4 7.5 7.5 7.7 7.9 49 91 69 11 55
22 7.6 7.4 7.8 7.7 8.1 28 76 5O 6 79
" " 5%... 23 7.8 7.7 8.1 7.7 8.1 44 48 60 67 100
24 7.7 7.7 8.0 7.8 8.1 42 66 45 56 100
acid, to estimated
pH 5.5 . . . . . . .. 29 5.5 5.5 5.2 5.5 5.9 31 57 15 0 25
30 5.3 5.4 5.3 5.5 5.8 30 52 3 0 25
acid. to estimated
pH4.5 . . . . . . .. 31 5.1 5.1 5.1 5.4 5.6 24 30 8 0 39
32 5.2 5.1 5.4 5.3 6.0 50 36 14 0 16
Kirvin ﬁne sandy
am
checks, untreated. 33 6.9 6.8 7.2 7.5 7.4 61 88 24 0 100
34 7.0 7.0 7.7 7.6 8.0 47 97 94 0 39
lime added, 1%... 39 7.4 7.4 8.5 8.4 8.5 64 93 40 8 33
40 7.6 7.5 8.6 8.6 8.8 47 95 0 0 29
" " 5%... 41 7.7 7.7 8.2 8.5 8.6 53 97 71 0 10
42 7.7 7.6 8.4 8.6 8.5 73 98 81 90 84
acid, to estimated
pH 6.5 . . . . . . .. 43 6.5 6.8 7.9 7.2 8.0 56 98 0 3 49
44 6.3 6.4 7.5 6.6 7.4 59 95 18 0 16
acid, to estimated
pH 5.5 . . . . . . .. 45 6.4 6.1 7.2 7.0 7.4 17 11 ‘ 14 0 18
46 6.1 6.3 7.2 6.3 7.6 58 92 10 17 4
acid, t0 estimated
pH 4.5 . . . . . . .. 47 5.8 5.9 6.6 6.0 6.4 44 70 44 44 90
48 6.0 6.3 6.9 6.3 7.2 8 15 14 8 28
Lufkin ﬁne sandy
loam .
check, untreated. . 63 6.1 6.1 6.9 6.3 44 57 0 0
1imeadded,1%... 51 7.4 7.6 7.8 8.0 8.2 46 68 4 3 0
52 7.4 7.5 7.9 8.0 8.1 26 33 17 11 50
acid. to pH 5.0... 53 5.5 5.6 6.0 5.5 13 2 0 O
54 5.2 5.6 5.6 5.4 0 2 0 0

16 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

the number of plants per box up to around 50. In 1929, root rot was
introduced at one end of the row of cotton in each box by inoculation
with naturally-infected cotton roots (13). Again in 1930, the boxes in
which the disease had not already developed as a result of successful over-
wintering were reinoculated. Thereafter, no further inoculations were
made. ‘The results for 1929 and 1930 therefore show the effect of the
various soils and treatments on the incidence of root-rot only; while
the 1931, 1932, and 1933 results are indicative of the effect of these con-

Table S. Incidence and persistence of Phymatotrichum root rot in boxes of
soil materials, of various soils, into which the additions speciﬁed were made.

   

Average pH of soil, Percentages of plants
for 0-2 feet deep attacked by root rot
Soil types and B 0X
treatments N o.
1929 1930 1931 1932 1933 1929 1930 1931 1932 1933
Tablor ﬁne sandy
am
checks, untreated. 1 5.7 5.9 5.7 5.9 5.9 51 100 53 31 0
2 6.2 5.8 5.8 6.0 6.1 38 95 38 6 O
manure, 20 tons "
per acre* . . . . .. 4 6.1 6.2 5.6 6.0 6.1 47 94 54 0 5
5 6.2 5.9 6.2 6.0 6.4 39 46 69 0 22
fertilizer, 4-8-4, 1
ton per acre, N
as nitrate of
soda* . . . . . . . . .. 3 6.2 6.0 5.9 5.9 6.3 53 96 4a4 0 0
6 6.0 5.9 5.7 5.7 5.8 45 87 13 0 0
sodium carbonate.
0.1% . . . . . . . . .. 11 7.4 6.4 6.6 6.5 6.5 8 0 0 0 0
12 7.3 6.4 6.6 6.8 6.7 6 0 0 0 0
gypsum,1% . . . . .. 13 5.0 4.9 4.9 4.9 5.1 s7 95 29 3 0
14 5.0 5.0 4.9 5.4 5.5 56 89 68 29 46
Susquehanna ﬁne
sandy loam
checks, untreated. 19 6.3 6.2 5.7 5.8 6.3 3 7 10 0 O
20 6.1 6.2 5.9 5.7 6.4 3 6 21 0 0
sodium carbonate.
0.1% . . . . . . . . .. 25 6.8 6.9 6.6 6.7 6.7 41 83 3 7 79
26 6.8 6.7 6.8 6.4 6.5 6 8 54 8 69
gypsum, 1% . . . . .. 27 5.6 5.5 5.4 5.5 6.0 47 94 76 48 86
28 5.5 5.6 5.5 5.5 5.9 43 79 17 18 31
Kirvin ﬁne sandy
am
checks, untreated. 33 6.9 6.8 7.2 7.5 7.4 61 88 24 0 100
34 7.0 7.0 7.7 7.6 8.0 47 97 94 0 39
manured, 40 tons
peracre* . . . . . .. 35 7.2 6.9 7.5 7.5 7.6 6 12 24 0 7
36 6.9 7.0 7.8 7.8 7.8 35 76 72 O 32
fertilizer, 4-8-4, 1
ton per acre, N
as cottonseed-
meal* . . . . . . . .. 37 7.1 .5 7.4 7.5 7.7 S6 91 72 0 70
38 7.0 6.8 7.0 6.9 7.3 69 92 38 O 29
borax, 2 1b., man-
ganese sulphate
50, potassium
iodide 5, iron
sulphate 50,
nickel sulphate
5. copper sul-
phate 10 lb. per
acre* . . . . . . . . .. 49 6.8 7.1 7.8 7.5 7.9 53 9O 58 88 82
5O 6.9 7.0 7.4 6.8 7.8 44 87 18 13 8

*Applications at the rates mentioned made twice, in 1929 and again in March, 1932, to upper 3
to 4 inches of soil only.

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT ~ 1.7

ditions on overwintering and ﬁnal survival of root rot. Occurrence of
root rot was favored in some seasons by watering. Root-rot notes Were
taken at the end “of each season, usually late in October or in November.
At this time, the roots of each third plant along the row were pulled and
examined. Roots of the intermediate plants were left in place in the
ground over winter to facilitate natural survival of the root-rot fungus.

Percentages of plants actually killed by root rot were usually not
markedly different from the total percentages attacked, which included
also those with infected roots but no aboveground symptoms. For this
reason, only the total percentages of the plants with root rot have been
tabulated in the present discussion of these results (Tables 7, 8, and 9).

Soil auger borings were made periodically in the boxes, and the pH
determined for each layer in each box. These extensive data cannot all
be summarized in this Bulletin; but averages of the pH values for the 0-2
ft. samples are given in Tables 7, 8, and 9. These averages are represen-
tative of the soil acidity for many of the boxes, in which the soil remained
at the same acidity to the entire depth of the containers. However,
in certain boxes the surface soil became more alkaline than deeper layers,
or the subsoil below 2 feet deep remained different from the upper
layers. Some of these exceptional cases will be discussed in consideration
of the results.

Effect of lime: Addition of lime made the soil more favorable for
root rot (Table 7). A pH of 7.4 to 8.0 was obtained in all the soils from
lime additions. There was little difference in the results between the 1%
and the 5% additions. Even at the lower rate, the soils became alkaline
and highly suited for the incidence and continued survival of root rot.

Eﬁect of sulphuric acid: The additions of sulphuric acid were effective
in eradicating root rot in the Tabor soil. The disease disappeared from
the check boxes of this series only after twice overwintering successfully.
Sufficient acid to change the soil to approximately pH 5.2-5.5 (boxes
15 and 16), however, eradicated root rot by the end of the ﬁrst year
following inoculation; that is, root rot overwintered once but not a.
second time. Greater acidiﬁcation, changing the soil to around pH 5.0
(boxes 17 and 18) prevented root rot from spreading at all from the
plants inoculated during the ﬁrst two years of the experiment, or
from surviving afterward by overwintering.

In the Susquehanna and Kirvin series, the acid did not eradicate root
rot, which survived in all the boxes until the end of‘ the experiment.
Results in the Lufkin series were obscured by the fact that root rot
failed to overwinter either in the check box 63, or in the acid boxes, 53
and 54.

Effect of manure: King and Loomis (9, 10, 11) in Arizona have found
that continued application of organic manures to cotton grown under
irrigation greatly reduced the extent of infection from root rot and
delayed the appearance of the disease. Root rot returned again when they
discontinued the annual application of manure.

18 BULLETIN NO. 545, 'I“EXAS AGRICULTURAL EXPERIMENT STATION

Fresh stable manure was applied to two boxes of the Tabor soil, at
20 tons per acre, in 1929 and again in 1932; and the Kirvin soil, which
was more favorable to the disease, was treated with manure at 4O tons
per acre in 1929 and 1932 (Table 8). In neither soil material did the
treatment eradicate root rot, which instead persisted in all four boxes
until the end of the experiment. In fact, since root rot failed to appear
in check boxes 1 and 2 of the Tabor series in 1933, during a season favor-
able for the disease, while it was present in the manured boxes, it might
even appear that manure aided in the survival of root rot in this case
rather than militating against it. These results resemble those of King
and Loomis in that no root rot appeared in the manured boxes in 1932,
following the reapplication of manure, while it came back again in 1933.
However, the season of 1932 was apparently highly unfavorable for root
rot in most of the containers of this experiment, so that this temporary
disappearance of the disease from the manured boxes cannot deﬁnitely be
ascribed to the treatments.

Effect of fertilizer: Four boxes of the experiment were used with addi-
tions of 4-8-‘4 fertilizers spaded into the surface soil in 1929 and again
in 1932 at the rate of 1 ton per acre each time. These fertilizers were
made up with superphosphate, muriate of potash, and nitrogen; sources
of nitrogen were nitrate of soda in the Tabor soil series, and cottonseed
meal in the Kirvin soil series. In the Tabor soil, root rot spread through-
out the fertilized boxes, just as in the checks, and overwintered success-
fully for one year after inoculations were discontinued, but failed to reap-
pear in the two following seasons. Meanwhile, root rot disappeared also in
the check boxes in the second year, though not in the ﬁrst. In the Kirvin
soil, root rot spread throughout the fertilized boxes, 37 and 38, as well
as through the check boxes, and overwintered successfully until the end
of the experiment despite the total of 2 tons of fertilizer per acre used
in these boxes.

These results indicate no apparent effect from the fertilizers on the
prevalence or overwintering of root rot. They agree in this respect with
other experiments (16), in which fertilizer salts added in very large
amounts to soil materials in large earthenware cylinders did not affect
incidence or overwintering of root rot, although additions of equal
weights of sodium chloride caused deﬁnite reduction in infection and
in death of plants. Plot experiments on Blackland prairie soils, summa-
rized recently by Jordan, Dawson, Skinner, and Hunter (8), led them
to the conclusion that continued fertilizer additions have increased yields
and caused deﬁnite though slight reductions in the proportions of cotton
plants killed by root rot.

Effect of rarer plant nutrients: One of the suggestions to explain the
continued prevalence of Phymatotrichum root rot in cultivated soils of
the Southwest has been the possible lack in the soils of some material
essential to plant growth, with the assumption that this lack either
makes plants susceptible to the disease or-directly aids the survival of
the fungus. Such an hypothesis would seem quite improbable from the
wide range of soil and climatic conditions obtaining through the thou-

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT 19

sands of square miles over which the root—rot fungus is destructive. It
was nevertheless considered advisable to add t0 this experiment a set
of boxes into which were incorporated a variety of chemicals, most of
which are known t0 be essential to plant growth, in low concentrations.
These materials are not usually included in fertilizer mixtures since
they are generally present in most soils and only small amounts are
needed by plants.

The additions made (in boxes 49 and 50) were calculated to supply the
following weights of the materials per acre of surface: manganese
sulphate 50 pounds, potassium iodide 5 pounds, iron sulphate 50 pounds,
nickel sulphate 5 pounds, copper sulphate 10 pounds, and borax 2 pounds.
These additions were repeated at the same rates in 1932. The results
showed no effect on the incidence or prevalence of root rot, which spread
rapidly in these boxes and survived until the end of the experiment.
Prevalence and destructiveness of root rot are therefore probably not
associated with lack of any of the various ions added to these boxes.

Effect of sodium carbonate: Additions of sodium carbonate (Table 8)
were made to adjust soils slightly toward alkalinity without at the same
time adding calcium. These additions of 0.1% to Tabor and to Susque-
hanna soil materials changed the average pH for the entire depth into
ranges (pH 6.4 to 7.4) deﬁnitely suitable for Phymatotrichum root rot.

With the Tabor soil (boxes 11 and 12) the treatment prevented any
spread of root rot from the plants inoculated in 1929, prevented develop-
ment of symptoms even on the inoculated plants in 1930, and prevented
any appearance of root rot thereafter from overwintering. However, the
sodium carbonate accumulated in the surface soil layer enough to darken
it visibly, to impede growth of the cotton plants, and to produce a reac-
tion of around pH 7.8 to 8.3 in the upper ten inches of soil as compared
with around pH 6.3 to 6.5 in the lower layers. Sodium carbonate here
was speciﬁcally inhibitory to Phymatotrichum root rot, since lime addi-
tions that produced the same pH were favorable for the disease. Appar-
ently development or survival of root rot is impeded by somewhat
lower concentrations of sodium carbonate than can be withstood by the
cotton plant, since cotton was grown successfully each year in boxes

11 and 12.

With the Susquehanna soil (boxes 25 and 26) the sodium carbonate
changed the surface soil layers to around pH 7.0-7.4, while the deeper
soil remained at around pH 6.0 to 6.6. The growth of plants in these
boxes was not interfered with by the treatment, nor was the develop-
ment of root rot, which exceeded that in the checks. The disease survived
until the end of the experiment, and caused losses every year, although
root rot disappeared from the check boxes after V1931. It is difficult to
explain why sodium carbonate controlled root rot in the Tabor soil but
not in the Susquehanna, except that the same soil conditions that held
the sodium carbonate dispersed throughout the soil and prevented accu-
mulation of it in the surface layer may have prevented it from acting on
the root-rot fungus.

20 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

It may be noted that these results agree with ﬁeld observations which
indicate that the cotton plant is more tolerant of “alkali” soils than
is the root-rot fungus. '

Effect of gypsum: Gypsum (calcium sulphate) was used to add calcium
without making the soil alkaline. It was of particular interest in com-
parison with lime additions, which increase both the pH and the calcium
content. Additions of gypsum amounting to 1% of the dry weight-of the
Tabor and Susquehanna soil materials made these soils highly acid
(Tables 10 and 11), and did not reduce the incidence or overwintering
of root rot. With the Tabor soil (Table 8, boxes 13 and 14), root rot
was approximately as prevalent as in the untreated checks. In the Sus-
quehanna soil, root rot was prevalent every year in the gypsum-treated
boxes (27 and 28), although it failed to become well established in the
checks. Since all treatments in the Susquehanna series appeared to im-
prove this soil for root rot, the results with gypsum here were of less
importance than if this soil had not seemed so readily transposed to a
favorable substratum. Nevertheless, root rot overwintered successfully
for three years and produced heavy percentages of infection in these
boxes which contained large additions of calcium sulphate.

Depth of acid layer of soil as aﬁecting development of root rot: Many
of the soils of Texas have developed from calcareous materials. Those
in which the surface is acid are in some cases over calcareous subsoils.
It was desired to ﬁnd how deep a layer of acid soil would be necessary to
prevent root rot from surviving in calcareous soil below. A series of
boxes of Lufkin ﬁne sandy loam soil, as outlined in Table 9, was set
up with lower alkaline layers to which 1% of limestone had been added.
Samples made periodically showed these lower layers to have reactions
usually between pH 7.3 and 8.0. The upper layers were acidiﬁed with
sulphuric acid to pH 5.5 to 6.2.

In 1929 and 1930, each box was inoculated. Root rot was abundant
in the boxes that were alkaline to the entire depth (boxes 51 and 52). In
the other boxes, however, it was generally conﬁned to the inoculated
plants. In 1931, root rot recurred only in the soil alkaline to the entire
depth and in the boxes with six inches of acid soil, and in the next
year, only in the boxes with alkaline soil to the entire depth.

These results would suggest that even a six-inch layer of acid surface
soil is suﬁicient to cause ﬁnal eradication of root rot, while a twelve-
inch layer may cause immediate disappearance of the disease. It must be
considered, however, that under the conditions of the experiment the
disease may not have become well established in the deeper alkaline
layers of this soil, and that therefore the experimental conditions here
may not have been comparable to ﬁeld conditions in which root rot
might have been indigenous for many years. For the same reason, these
results can scarcely be interpreted as proving that root rot could be
eliminated from infested areas by some treatment that would make the
upper six to twelve inches of the soil unfavorable for the root-rot fungus.

Root rot as inﬂuenced by changes in soil acidity: The experiment sum-
marized in Tables 7, 8, and 9 has furnished information on the suitability

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT 21

Table 9. Incidence and persistence of Phymatotrichum root rot in boxes 0f
Lufkin ﬁne sandy loanl soil material, xvith upper layers adjusted
t0 acidity by addition of sulphuric acid to estimated pH 5.0,
and lower layers adjusted to‘ alkalinity by addition
of 1 per cent limestone.

Depth of acid and alkaline pH of soil of the Percentages of plants
soil layers acid layers attacked by root rot
Box
No.
Acid Alkaline
layer layer 1929 1930 1931 1932 1929 1930 1931 1932
inches inches a

 0-36 51     46 68 4 3
S2     26 33 17 11

0-6 6-36 5S 5.7 6.8 5.3 6.3 5 4 12 0
56 5.6 6.9 6.2 6.5 19 7 20 0

0—12 12-36 S7 5.6 5.9 5.5 5.7 O 8 O O
58 5.6 6.5 5.8 6.1 11 4 0 0

0-18 18-36 59 5.5 6.2 5.1 5.6 33 5 0 0
60 5.6 6.0 5.5 5.8 6 6 0 0

0-24 24-36 61 5.5 5.8 5.3 5.6 11 4 0 0
62 5.4 5.7 5.4 5.5 O 8 0 O

0-36  53 5.5 5.6 6.0 5.5 13 2 0 0
54 5.2 5.6 5.6 5.4 0 2 0 0

to root rot, under somewhat controlled conditions, of four different soil
types following treatments with lime, sulphuric acid, gypsum, sodium
carbonate, manure, and fertilizer. These results were discussed above
chieﬂy with regard to the effect of the materials as such on the incidence
or overwintering of root rot. In general, soils that became more acid
were less suited to root rot, and soils that became more alkaline were
more suited for the disease. Additions of lime have invariably made the
soil deﬁnitely alkaline and deﬁnitely favorable for root rot. Similarly, in
the manured and fertilized soils, differences in the amount of root rot
may well have been due to chance, and the soil acidity was apparently
not of importance. With the boxes to which gypsum was added, however,
rather deﬁnite acidiﬁcation of the soil was not followed by reduction in
the incidence or overwintering of root rot. These exceptional cases are
examined more fully below. The complete data on hydrogen-ion concentra-

tions of samples from the gypsum boxes are given in Tables 10 and 11,,

along with similar data for the untreated soil and sulphuric-acid treated
soil of the Tabor and Susquehanna series.

It should be noted ﬁrst, from Table 10, that the deeper layers of
soil in both of the gypsum-treated boxes became very acid. These
deeper layers would not explain the difference in the survival of
root rot in these boxes. It diminished slowly in box 13, to disappear in
1933, while it survived in the other box, 14. Changes in the 0-10 inch
soil layer, on the other hand, correlate with this course of events. In
box 14, this surface layer did not become more acid than pH 5.7, and by
the end of 1931 had changed back toward neutrality; but in box 13, the
acidity in this layer became more intense than pH 5.5, going at the end
of 1931 to pH 5.1. A similar relation appears in the boxes of this series

22 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

Table 10. Detailed soil reaction data for a few boxes of the Tabor ﬁne
sandy loam series, showing pH determinations on samples
taken at the various dates indicated.

pH of soil samples from following depths,
Date inches:
Soil treatments Box of taking
No. samples "

0-10 10-18 18-25 25-32 32-36

Checks, untreated . . . . . . . .. 1 Oct. 6, 1929 6.1 5.0 5.9 7.3 7.5
Feb. 27, 1930 6.2 5.6 5.8 6.0 7.2

Mar. 19,1931 6.1 5.6 5.3 5.7 6.5
Dec. 4. 1931 7.9 4.9 5.3 6.1 7.6

NOV. 18, 1932 6.8 5.4 5.4 6.6 6.9

Jan. 9, 1934 6.9 5.3 5.5 5.7 . 7.5
2 Oct. 6,1929 6.9 5.8 5.9 6.0 7.5
Feb. 27,1930 6.2 5.6 5.7 5.9 7.2
Mar. 19, 1931 6.9 5.4 5.1 5.4 6.4
Dec. 4, 1931 7.2 5.7 5.5 5.6 7.5

Nov. 18, 1932 6.9 5.6 5.4 5.5 7.1
Jan. 9, 1934 7.2 5.7 5.4 5.5 6.3
Gypsum, 1% . . . . . . . . . . . .. 13 Oct. 6,1929 6.0 4.4 4.7 4.9 6.3
Oct. 26, 1929 6.1 4.3 4.5 5.6 5.9
N0v.27, 1929 5.9 4.2 4.5 4.6 5.7
d0 5.8 4.2 4.4 4.8 5.6
Feb. 27, 1930 5.9 4.3 4.4 5.5 5.6
Mar. 19, 1931 5.7 4.6 4.5 5.1 5.5
Dec. 4, 1931 5.1 4.5 4.2 4.1 5.6
NOV. 18, 1932 6.2 4.3 4.3 4.7 5.6
Jan.9, 1934 6.5 5.5 5.0 5.2 5.3

14 Oct. 6,1929 6.1 4.4 4.5 4.7 6.1
Oct. 26. 1929 5.9 4.4 4.6 4.6 6.3
Feb. 27. 1930 6.1 4.3 4.5 4.7 5.6
Mar. 19, 1931 5.7 4.6 4.5 5.1 5.3
Dec. 4, 1931 6.4 4.2 4.2 4.6 5.4
Nov. 18, 1932 7.1 4.5 4.6 5.0 5.7
Jan. 9, 1934 7.0 4.8 4.7 5.0 5.3
Acid, to estimated pH 5.5. 1S Oct. 6, 1929 5.9 5.6 5.3 5.5 5.6
Oct. 26. 1929 5.8 4.8 4.7 4.9 5.0
NOV. 27,1929 5.6 4.7 4.7 4.7 5.4
do ~ 6.0 4.8 4.6 4.7 5.3

Feb. 27,1930 5.6 4.9 4.9 5.5 5.7
Mar. 19, 1931 5.2 5.0 5.1 5.0 5.0
Dec. 4, 1931 5.6 4.8 4.8 4.8 5.0

Nov. 18,1932 5.8 5.1 4.9 4.8 5.5
Jan. 9, 1934 6.3 5.2 5.1 5.3 5,2
16 Oct. 6, 1929 5.9 5.4 5.4 5.4 5.4
Oct. 26, 1929 5.6 5.0 5.1 5.1 5.1
Nov. 27, 1929 5.8 4.8 4.7 4.7 5.3
do 5.7 4.7 4.7 4.7 5.3

Feb. 27, 1930 5.8 5.4 5.4 5.6 5.7
Mar. 19, 1931 5.4 5.1 5.0 5.3 5.4

Dec. 4, 1931 5.2 5.1 5.0 5.0 5.5
NOV. 18, 1932 6.2 5.2 5.3 5.2 5.2

Jan. 9, 1934 5.6 5.3 5.1 5.2 5.7
Acid, to estimated pH 4.5. 17 Oct. 6, 1929 5.2 5.4 5.0 5.1 5.4
Oct. 26, 1929 4.6 4.5 4.5 4.6 4.7
NOV. 27, 1929 5.4 4.6 4.6 4.8 5.4

0 5.4 4.6 4.7 4.6 5.2
Feb. 27,1930 5.4 4.9 4.8 4.9 5.2
Mar. 19, 1931 5.2 5.0 4.8 4.8 4.8

Dec. 4, 1931 5.4 4.8 4.8 4.8 5.1
Nov. 18, 1932 5.9 5.1 4.9 5.4 5.4
Jan. 9, 1934 6.0 5.5 5.2 , 5.3 5.5
18 Oct. 6,1929 6.2 5.3 5.3 5.2 5.4
Oct. 26, 1929 4.8 4.8 4.7 4.8 5.0

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT 23

Table 10. Detailed soil reaction data for a few boxes of the Tabor ﬁne
sandy loam series, showing pH determinations on samples
taken at the various dates indicated.—(Continued)

pH of soil samples from following depths,

Date inches:
Soil treatments Box of taking
. N0. samples

0-10 l 10-18 18-25 25-32 I 32-36

 

l

Nov. 27, 1929 5.5 4.6 4.7 4.8 5.2

do 5.3 4.4 4.4 4.6 4.7
Feb. 27,1930 5.6 4.7 4.7 4.7 4.9
Mar.19, 1931 5.3 4.9 4.7 4.5 4.6
Dec.4, 1931 5.5 5.0 5.1 5.7 5.4
Nov.18, 1932 5.7 5.1 5.3 5.9 5.9
Jan.9, 1934 6.1 I 5.3 5.3 5.3 5.5

to which sulphuric acid Was added. Root rot was never able to become
established in boxes 17 and 18, only the inoculated plants being killed;
but in boxes 15 and 16, root rot spread well in 1929 and 1930, over-
wintered to cause some loss in 1931, and then disappeared. In all four
of these boxes, the deeper soil layers were generally more acid than pH
5.5, and frequently beyond 5.0. However, the reaction of the surface
layer of soil in boxes 17 and 18 was usually more acid than pH 5.5
during the entire period of the experiment, while in boxes 15 and 16
the reaction did not pass this point until 1931, after which time root rot
disappeared from these boxes. Root rot disappeared from boxes 15 and
16, in which the deeper soil layers became much less acid than in
box 14, from which it was not eradicated. However, the surface soil
of boxes 15 and 16 became more acid than that of box 14.

The results of the Susquehanna soil series can be interpreted similarly
from the hydrogen-ion concentration data given in Table 11. Root rot was
not controlled here despite the deﬁnite acidiﬁcation of the lower layers
of the soil by acid (boxes 31 and 32) and by gypsum (boxes 27 and
28). But in none of these boxes did the uppermost soil layer become as
acid as pH 5.5, and the next layer, 31/2-10 inches deep, passed this point
in the acid boxes but not in the gypsum boxes, in which root rot was
much the more destructive.

This line of reasoning indicates a tentative conclusion that, under
the conditions of this experiment, acidiﬁcation of the surface soil to
at least pH 5.5 was necessary to produce rapid changes in the prevalence
of root rot. More extreme acidiﬁcation of the deeper soil, with the
surface layer left near neutrality, was not suﬁicient to eradicate the
disease. As shown above (Table 9), under the reverse conditions, with
an acid surface layer and a calcareous, alkaline subsoil, root rot was
apparently controlled by the presence of a six to twelve-inch acid surface
layer of soil. These results agree in showing the apparent crucial impor-
tance of the surface soil layer in determining the effectiveness of soil
acidity in limiting development and overwintering of root rot.

While these results thus agree with earlier work in showing a corre-
lation between the pH of the soil and the prevalence of root rot, they

24 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

do not furnish any deﬁnite information on the particular factors effective
in causing the correlation. The data above do not furnish conclusive
evidence that the determining factor in the instances cited was the

Table 11. Detailed soil reaction data for a few boxes of the Susquehanna
ﬁne sandy loam series, showing pH determinations 0n samples
taken at the various dates indicated.

pH of soil samples from following depths,
Date inches:
Soil treatments Box of taking
No. samples

06% 3%-10 10-16 16-26 26-36

Checks, untreated . . . . . . . .. 19 Oct. 6, 1929 6.9 6.4 6.0 5.7 5.7
Feb. 27,1930 6.7 6.5 5.8 5.8 6.2

Mar. 19, 1931 6.2 6.5 4.6 5.5 5.4

Dec. 4, 1931 6.7 6.6 5.2 5.3 5.3

Nov. 18, 1932 6.4 6.6 5.1 5.1 5.6

Jan. 9, 1934 7.0 6.9 5.6 5.5 5.7

20 Oct. 6, 1929 6.9 6.8 5.9 5.6 5.7
NOV.27,1929 6.7 6.0 5.4 5.6 5.5

do 6.9 6.1 5.5 5.4 5.5

Feb. 27, 1930 6.9 6.6 5.7 5.7 6.1

Mar. 19,1931 6.7 6.1 5.6 5.3 5.3

Dec. 4, 1931 6.6 6.4 5.4 5.4 5.4

Nov. 18, 1932 6.1 6.1 5.3 5.1 5.1

Jan. 9. 1934 7.1 7.0 5.6 5.7 5.5
Gypsum, 1% . . . . . . . . . . . .. 27 Oct. 6.1929 6.9 6.4 4.7 4.6 4.9
Oct. 26,1929 6.8 6.3 4.6 4.5 4.5

Feb. 27, 1930 6.6 6.3 4.6 4.6 4.6

Mar. 19, 1931 6.3 5.9 5.0 4.5 4.4

Dec. 4, 1931 6.2 6.5 4.7 4.4 4.6

Nov. 18,1932 6.4 6.3 4~.8 4.6 5.1
Jan.9, 1934 7.3 7.1 5.1 4.5 5.2

28 Oct. 6, 1929 6.8 6.2 4.4 4.4 4.8
Oct. 26, 1929 6.8 6.1 4.4 4.6" 4.7

Feb. 27, 1930 6.7 6.3 4.5 4.7 4.8

Mar. 19, 1931 6.5 6.4 4.9 4.3 4.5

Dec. 4, 1931 6.8 6.2 4.4 4.2 4.5

Nov. 18,1932 6.5 6.3 4.7 4.3 4.5

Jan. 9, 1934 7.1 6.5 5.6 4.4 4.6
Acid, to estimated pH 4.5. 31 Oct. 6, 1929 6.0 6.0 4.6 4.6 4.8
Oct. 26, 1929 5.7 4.9 4.4 4.5 4.6

Nov. 27, 1929 6.4 5.8 4.6 4.4 4.5

do 6.0 5.5 4.5 4.4 4.5

Feb. 27, 1930 5.6 5.7 4.5 4.5 4.7

Mar. 19,1931 5.7 5.2 4.8 4.5_ 4.6

Dec. 4,1931 6.2 5.1 4.5 4.4 4.6

Nov. 18. 1932 6.0 6.2 4.8 4.7 5.2

Jan. 9, 1934 6.5 6.2 4.8 4.8 4.9

32 Oct. 6,1929 5.7 6.3 4.7 4.6 5.1
Oct. 26, 1929 5.8 5.5 4.4 4.4 4.6

Nov. 27, 1929 5.9 5.6 4.7 4.4 4.6

do 5.9 5.6 4.3 4.2 4.5

Feb. 27, 1930 5.7 5.5 4.6 4.5 4.8

Mar. 19, 1931 6.0 5.9 5.0 4.7 4.8

Dec. 4, 1931 5.6 5.3 4.5 4.6 4.9

NOV. 18, 1932 5.6 5.8 4.9 5.0 5.1

Jan. 9, 1934 6.8 6.3 5.0 4.8 5.4

hydrogen-ion concentration alone. But it is obvious that continued prev-
alence of root rot in this experiment was associated more closely with
the ﬁnal pH of the soils than with original differences in the soil types.

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT 25

Lufkin Fine Sandy Loam Soil Acidiﬁed at Various Depths and with
Inoculum at Various Depths.

This experiment was set up in the spring of 1929, with some of the
Lufkin ﬁne sandy loam soil material, as used in the preceding experiment,
in a series of 16 smaller wood boxes, 2 feet in each dimension. This soil
was adjusted either to alkalinity by addition of 1% of ground limestone,
or to acidity by addition of sulphuric acid calculated to change the soil
t0 pH 5.0. As indicated in Table 12, in four of the boxes the soil was
made alkaline to the entire depth of two feet; in another four boxes,

Table 12. Incidence and persistence of Phymatotrichum root rot in Lufkin
ﬁne sandy loam soil material adjusted as indicated.

 

Percentage of cotton
plants succumbing to
Box Location root rot
Soil reaction No. of inoculum

1929 1930

All alkaline (pH 7.2-8.0) . . . . . . . . . . . . . . . . . . . 1 In upper foot of soil 100 67
2 do 67 O

3 In lower foot of soil 0 0

4 do 100 100

All acid (pH 4.9-5.5) . . . . . . . . . . . . . . . . . . . . . . 5 In upper foot of soil 0 0
' 6 do 0 0

7 In lower foot of soil 0 0

8 do O O

Upper foot acid, lower foot alkaline . . . . . . . . . 9 In upper foot of soil 17 0
1O do 17 O

11 In lower foot of soil 0 0

12 do 0 0

Upper foot alkaline, lower foot acid . . . . . . . . . 13 In upper foot of soil 83 0
14 do 100 100

15 In lower foot of soil 0 0

16 do O 0

the soil was made acid to two feet deep; in four more, the upper foot of
soil was made acid and the lower foot alkaline; and in the ﬁnal four,
the upper foot was made alkaline and the lower foot acid. The upper
foot of soil in each box was a brownish-gray ﬁne sand and the subsoil
was a stiff gray clay.

Cottonwas planted in these boxes in 1929 and 1930. In 1929 the plants
were thinned to 6 plants per box, and in 1930 to 8-20 plants per box.
In 1929, two plants in each box were inoculated heavily with root rot.
The inoculum consisted of the roots of freshly-wilted cotton plants,
trimmed down to exactly eight inches in length. Four roots were used
for each plant to be inoculated. In two of each set of boxes, the inoculum
was placed in the upper foot of soil by inserting it in holes bored to a
depth of 1O inches with a soil auger; in the other two boxes, it was
placed in the lower foot of the soil in holes bored to 22 inches.

26 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

The results obtained are shown in Table 12. It will be noted that
when the boxes were ﬁrst inoculated root rot killed most of the plants
in the alkaline soil (boxes 1-4), but none of those in the acid soil
(boxes 5-8). In boxes with the upper soil acid and the lower soil alkaline,
root rot killed only two of the plants in the boxes in which the inoculum
was placed in the acid surface soil (boxes 9 and 10), and. did not appear
in boxes 11 and 12 in which the inoculum was placed in the lower
alkaline soil layers. In the boxes with alkaline surface soil and acid
subsoil, root rot again appeared only in the boxes inoculated in the
upper soil layer, and killed most of the plants in boxes 13 and 14.

The ﬁnal column shows the prevalence of root rot after wintering
over in these boxes. The disease did not appear in 1930 in the boxes
with the soil acid throughout or in the boxes with acid soil in the
surface layer. It reappeared only in boxes 1 and 4, with the soil alkaline
throughout, and in box 14, in which the upper foot was alkaline and
the lower foot was acid.

In this experiment, the hydrogen-ion concentration of the upper layer
of soil was apparently of importance in limiting the development of
root rot, while the pH of the deeper soil layer did not appear to affect
the results under these conditions. Thus, root rot was introduced in
1929 on plants with the deeper roots in deﬁnitely alkaline soil (boxes 9
and 10), yet the disease did not become established there to reappear
in 1930. Meanwhile, the disease had killed most of the plants in boxes
13 and 14, with the upper alkaline’ soil underlain by acid subsoil, and
overwintered successfully in one of these boxes.

EXPERIDIENTS WITH SOIL AOIDIFIOATION AS A POSSIBLE MEANS
OF CONTROL

The various experiments summarized above demonstrate that prev-
alence and destructiveness of root rot is closely correlated with the
acidity or alkalinity of the soil. Acid soils are always less favorable for
root rot, while alkaline soils are more favorable. It has therefore
appeared possible that root rot might be controlled by acidiﬁcation of
the soil. Soil acidiﬁcation has been attempted in a number of experiments
by the application of sulphur, which is eventually oxidized in soils to
sulphuric acid.

In an experiment at the Temple, Texas, substation, yearly additions
of 10,000 pounds per acre of sulphur were disked into the surface soil
in plats of Bell clay (a calcareous soil) from 1920 to 1926. The soil
did not become acid nor was there any apparent change in prevalence of
root rot (12, 18). This indicated that acidiﬁcation would probably not
be a useful means of control in highly calcareous soils.

In the fall of 1927, sulphur was applied (by H. E. Rea) in empirical
amounts in a series of ﬁeld tests with soils that are not highly calca-
reous. The large amounts of sulphur used acidiﬁed the surface suﬂi-
ciently to injure crops in 1928 and 1929 (15), while root rot persisted
in- the sub-surface soil (which remained alkaline) and attacked the

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT 27

deeper roots of the plants. These tests showed that soils not highly
calcareous could be acidiﬁed, but that care would be needed to obviate
crop injury from excessive acidity. The three experiments summarized
below were tests of the effect of sulphur in possible control of root rot
under somewhat controlled conditions.

Preliminary Test of Plain and Oxidized Sulphurs in Small Containers

In connection with the possibility of using sulphur for soil acidiﬁ-
cation for possible control of root rot, the question was considered
whether it would be desirable to use for such purpose sulphur to which
had been added materials to hasten the oxidation in the soil to form
sulphuric acid. An experiment was set up in which eight different
commercial sulphur preparations were tested, each at three rates of ap-
plication, in small metal containers. On June 12, 1928, these sulphurs
were incorporated at rates of 5,000, 10,000, and 15,000 pounds per acre
into the surface one or two inches of soil of the Crockett clay loam
surface soil material used, and were still present in large lumps at these
depths at the end of the season. The acidity that developed was ap-
parently largely localized during the period of this experiment to the
upper soil in which the sulphur was placed. The lower roots of some
of the plants were attacked by root rot, while parts of the tap-roots, in
the acid surface soil, showed acid injury.

Cotton was planted, thinned to about four plants per container, and
inoculated with root rot. At the end of the season, all the plants were
pulled and the roots examined. It was found that many plants had been
killed by acid injury, as shown by the characteristic enlarged cracked
regions and the absence of Phymatotrichum strands. Plants with acid
injury were more abundant in the series with higher rates of application
of sulphur than in series with 5,000 pounds per acre, and were more
abundant in series in which the soil actually became highly acid than
in less acid soil.

Root rot, on the contrary, was much less destructive in the acid soils.
While some of the plants in the soils treated with sulphur developed
traces of root rot, usually only on the tips of the roots, the disease
killed only three per cent of the plants in the series receiving 5,000
pounds of sulphur per acre, one per cent in the 10,000-pound series,
and none in the 15,000 pound series (Table 13). Meanwhile, forty per

.cent of the check plants had been killed by root rot.

In this experiment, more intense acidities were developed in the soil
to which the sulphur containing oxidizing materials had been added,
than in the soils with sulphur alone. There was correspondingly greater
sulphur injury on plants in these series than on plants in the plain
sulphur series. Root rot occurred on plants in the series treated with
commercial ﬂour of sulphur or with mixtures containing sublimed
ﬂowers of sulphur, to a greater extent than in series treated with velvet
ﬂowers of sulphur or with mixtures containing the adhesive ground

28 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

Table 13. Root rot and acid injury of cotton plants grown in small
containers of Crockett clay loanl surface soil material
treated with plain and oxidizing sulphurs;

4 containers per series except 12 used
for checks; 4 plants per container.

Percentages of plants:
Rate, I
Material lbs, per pH killed killed
acre with by with by
root root sulphur sulphur
rot rot injury injury
Velvet ﬂowers of sulphur . . . . . . . . . . . 5,000 3.8-5.7 0 0 0 0
10,000 2.7-3.1 0 0 13 0
15,000 2.9-3.9 0 0 20 0
Commercial ﬂour of sulphur . . . . . . . . 5,000 3.8-4.2 41 0 23 0
10,000 2.8-2.9 25 0 19 0
15,000 3.9-4.0 37 0 44 0
Sublimed ﬂowers of sulphur plus
KlWnO4 as oxidizing agent. . . . . . . 5,000 3 6-3.8 50 0 93 7
10,000 2 3-3.1 6 0 38 13
15.000 2 6-2.8 0 57 44
Adhesive ground sulphur plus
KMHO4 as oxidizing agent . . . . . . . . 5.000 2 3-4.1 0 0 0
10,000 2 4-3.0 7 0 28 7
15,000 2 5-2.6 0 0 73 13
Sublimed ﬂowers of sulphur plus
catalytic oxidizing agent . . . . . . . . . . 5.000 3 1-3.3 28 14 14
10.000 2 6-3.0 0 O 29 0
15,000 2 8-3.3 O O 35 14
Adhesive ground sulphur plus
catalytic oxidizing agent . . . . . . . . . . 5,000 3 0-3.5 0 0 14 7
10,000 2 2-2.9 0 O 92 0
15,000 2 1-2.6 0 0 100 43
Sublimed ﬂowers of sulphur plus
KMnO4 and catalytic oxidizing
agent . . . . . . . . . . . . . . . . . . . . . . . . . . 5,000 3 9-4.1 14 7 0
10,000 2 5-2.8 7 7 0 0
15.000 2 l-3.3 0 0 23 0
Adhesive ground sulphur plus
KMnO4 and catalytic oxidizing
agent . . . . . . . . . . . . . . . . . . . . . . . . . . . 5,000 2 5-3.7 0 0 14 0
10,000 2 6-3.0 0 O 27 0
15.000 2 1-2.9 0 0 34 7
None, checks . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2-6.0 62 40 0 0

sulphur. The diﬁerence was not accompanied by a difference in the
ﬁnal pH in these series, but may have been due to differences in speed
of initial acidiﬁcation. Mortality from root rot was negligible in all the
treated series.

These results conﬁrmed the general conclusion that suﬁiciently acid
soils will prevent successful attack of plants by Phymatotrichum root
rot, even when the disease is introduced by artiﬁcial inoculation. The

rates of materials used here were excessive and caused injuries to the.

plants in the ﬁrst year, with total failure to secure a stand in the fol-
lowing year; hence these results did not point toward practical applica-
tion of sulphur for control of the disease.

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT 29

Sulphur Applied at Various Depths in Small Plats

This experiment was planned to determine whether sulphur mixed to
various depths with the soil would be able to exclude root rot. The
location used for the experiment was a plat, originally of Lufkin ﬁne
sandy 10am soil, that had been used for years as a garden and in which
root rot had not appeared. The soil Was quite favorable for root rot,
as shown by the pH of 6.8 to 7.6, ,and by successful inoculations in
nearby plats as well as in the plats of this experiment. For the treat-
ments, nine small plats each ten feet long and six and one-half feet wide
were used, and an adjoining larger area was used for a check plat
(Table 14). Finely-ground sulphur was worked in to depths of 4 inches

Table 14. Sulphur applied to‘ various depths in small plats of Lufkin ﬁne
sandy loam soil.

Rates of actual sulphur
Plat Depths of soil layers in Factor by which estimated application, in soil layers
No. which sulphur applied sulphur rate multiplied * speciﬁed T, pounds per acre
inches I

1 0-4 1 % 2,400
2 0—6 1% 2,934
6—12 1,866

3 0—6 1 % 2,134
6—12 1,866

12-24 3,732

4 0-4 2 2,400
5 0—6 2 2,400
6—12 2,800

6 0—6 2 3,600
6—12 2,800

12-24 5,600

7 0-4 3 4,800
8 0—6 3 1,200
6—12 4,200

9 0—6 3 1,200
6—12 4,200

12—24 8,400

10 . . . . . . . . 0

*Estimated rates determined by laboratory tests of samples from the various soil layers in each
plat, to ﬁnd amounts of sulphur needed to reach pH 5.0, were then multiplied by the factors
given to obtain the rates of application.

TTotal applications per plat were sums of those speciﬁed for the various soil layers.

in three of the plats, to 12 inches in three plats, and to 24 inches in
the remaining three treated plats. Each of the three plats treated to
a similar depth was treated at a different rate. The rates were calcu-
lated from laboratory tests, by the method of Fraps and Carlyle (7), on
samples of soil from the layers of each plat, to determine the amounts
of sulphur required to convert the soils to around pH 4.5 if all the
sulphur were oxidized immediately. Since all the sulphur would not be
oxidized at any one time, it was assumed that the maximum acidity to

3~0 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

be expected from such an addition would be around pH 5.0. To provide
suitable variations in the treatments, the rates arrived at from these
determinations were then arbitrarily multiplied by factors of either 1%,
2, or 3. Thus plat 1 was treated t0 a depth of 4 inches with 1%; times the
amount of sulphur estimated necessary to produce pH 5.0; and so on.

These applications were made by digging away the soil to the re-
quired depth in the various plats, and then mixing in the sulphur with
the proper soil layer as it was replaced. The sulphur was thus mixed
much more thoroughly with the soil than could be done under ﬁeld
conditions, the object of the experiment being to ﬁnd Whether under
such optimum conditions of application the materials applied would be
able to exclude root rot from these plats. The sulphur applications
were completed in April, 1930.

Table 15. Changes in soil acidity produced by addition of sulphur to plats
of Lufkin ﬁne sandy 10am soil.

Total amounts of sulphur, Mean pH of soil samples, on the dates
as lb. per acre, and depths speciﬁed, from the following depths:
Plat to which applied Date of soil
No. samples l
0-6 | 6-12 12-18 18-24 24-30 30-36
Pounds Inches inchesfnches inches inchesinchesinches

1 2,400 0-4 Feb. 20,1931 5.8 6.3 6.5 7.1 7.3 7.8
Apr. 11,1932 6.9 6.6 6.6 6.8 7.2 7.6

Nov. 30,1932 7.2 6.7 6.6 7.0 7.1 7.4

2 4.800 0—12 Feb. 20,1931 5.7 5.9 6.3 7.4 7.6 7.9
Apr. 11, 1932 6.3 5.4 5.7 6.4 7.0 7.4

Nov. 30.1932 5.6 5.5 5.4 6.6‘ 6.8 7.4

§' V‘

3 7,732 0-24 Feb. 20, 1931‘ 5.5 4.8 4.7 5.3 7.0 7.6
Apr. 11, 1932 6.3 5.8 5.5 5.6 6.0 7.1

Nov. 30, 1932 5.9 4.9 5.0 5.1 5.8 7.0

4 2,400 0-4 Feb. 20, 1931 4.5 4.9 5.7 6.6 7.3 7.8
Apr. 11,1932 6.7 6.2 5.8 6.3 6.8 6.6

Nov. 30, 1932 6.1 5.7 5.7 5.9 6.7 7.1

5 5,200 0-12 Feb. 20,1931 5.2 4.6 5.1 5.8 6.9 7.5
Apr. 11. 1932 6.2 4.3 5.5 6.2 6.7 7.0

Nov. 30, 1932 6.6 5.4 5.3 5.8 6.6 7.0

6 12.000 0-24 Feb. 20,1931 i 4.0 3.8 4.0 4.4 4.8 6.8
Apr. 11, 1932 5.4 4.5 4.3 4.2 5.2 6.3

Nov. 30, 1932 5.0 4.5 4.4 4.5 4.5 5.5

7 4,800 0—4 Feb. 20,1931 3.9 4.2 5.7 5.5 6.7 6.6
Apr. 11. 1932 4.8 4.8 5.6 5.8 6.2 7.0

Nov. 30,1932 5.3 4.9 5.5 5.7 6.2 6.9

8 5.400 0~12 Feb. 20. 1931 5.5 3.4 4.8 6.1 6.8 7.2
Apr. 11, 1932 5.6 4.8 5.6 5.9 6.7 7.0

Nov. 30, 1932 6.8 4.5 4.5 5.0 5.9 6.5

9 13.800 0-24 Feb. 20, 1931 6.0 4.2 3.8 4.1 5.7 7.0
Apr. 11,1932 6.4 4.6 4.5 4.5 5.2 6.1

Nov. 30,1932 6.9 4.8 4.5 4.2 4.5 5.9

10 None, check . . . . . . . . . . .. Feb. 20, 1931 8.3 8.1 8.1 8.0 8.0 8.1
Apr. 11.1932 8.4 8.4 8.1 7.8 7.8 7.8

Nov. 30,1932 8. 8.7 .3 8.1 7.9 7.9

Cotton was grown in the plats in 1930, 1931, and 1932, and irrigated
at about 10-day intervals. Root rot was introduced by artiﬁcial inoc-

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT 31

ulation (13), in the center of each plat, in 1930 and 1931. The plants
inoculated were ‘marked by stakes, and notes taken to indicate possible
spread as well as the ﬁnal percentages of plants with root rot. At the
end of the season, notes were taken on aboveground symptoms of root
rot, and in addition the root of at least one plant in each three Was
pulled and possible underground infection noted.

In 1930, root rot attacked only plants around the points of inocula-
tion in the treated plats. During 1931, root rot killed many plants
along the outer rows of the treated plats (Fig. 1). These plants prob-

ably became infected by the disease spreading along roots found ex-

tending entirely outside of the treated plats into infested areas. It is
to be noted that soil samples taken (in April, 1932) outside of several
treated plats showed that the sulphur applied within these plats had
caused only insigniﬁcant changes in the pH at distances as close as 3
inches outside of the plats. During the same 2-year period since the
sulphur had been applied, the soil in these plats had become deﬁnitely
acid to 30 inches deep from sulphur applied to a depth of only 4 inches
(Table 15). This is in line With the general conclusion that horizontal
movement of soil solutes is much less than vertical movement.

While root rot had become established only at occasional points in
the treated plats, it had spread rapidly in the untreated check plats,
and in 1931 and 1932 attacked most of the plants.

In the treated plats, root rot became of importance only in 1932. In g

that year it spread in from the edges, as Well as from the few points
toward the center of some of the plats in which it had become estab-
lished, and attacked most of the plants in plats 1, 2, 5, 7, 8, and 9

Table 16. Incidence of Phymatotrichum root rot in Lufkin ﬁne sandy loam
plats into which sulphur applied at various rates and to various depths.

1930 results 1931 results 1932 results
Total amounts of ‘
sulphur. as lb. per Per cent of Per cent of Per cent of
Plat acre, and depths plants— plants—— plants——
No. to which applied No. of No. of No. of
plants With plants With plants With _
root Killed root Killed root Killed
Pounds Inches rot rot rot

1 2,400 0-4 134 1 O 129 22* 21 154 82 77
2 4,800 0-12 84 1 1 135 21* 18 146 64 62
3 7,732 0-24 98 3 O 146 19* 8 145 36 35
4 2,400 - m4 74 o o 119 9 7 171 11 1o
5 5,200 0—12 108 0 0 123 1 0 167 58 53
6 12,000 0-24 73 0 O 159 0 O 165 5 4
7 4,800 0-4 75 1 O 111 7* 5 135 53 47
8 5,400 0-12 133 6 6 144 34* 32 138 85 80
9 13,800 0—24 115 2 0 134 8* 7 125 80 68
10 None, check . . . . . . . . 130 27 18 297 92 72 265 85 77

*Some or all of plants with root rot atledge of treated plat, adjoining untreated plat in which
root rot prevalent.

32 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

(Table 16). Distribution of the disease was limited to certain portions
only of plats 2, 3, 4, 5, and 7 (Fig. 1), and accordingly soil samples
were taken from the plats at locations selected in such a way as to ﬁnd

' 9 3 ° I 9 3 I | 9 3 2
Pm I Flu 2 Pm 3 Pm I Pm 2 Plm 3 Pm I Pin 2 Pm 3
p ii : r131: 11:: tn : :: i :—
'» = — I n" c: I: |@ n @
~~ t < 7 ' , IF I Q ﬁ Q @ {I
u Ii i Ilni :
Pia \~ Pm 5 Pin b Pm w Pin 5 Pm b Pm w P131 5 pm 5
_ -: | | I
i I ‘ Q | I In-l I-
‘ ' - ' ® I ® © I
‘T Q I Q :l Il—l I
Pin 7 Pin 8 P's! 9 Pm 7 Pm g pm 9

I
,1
II ||
I

   

I Pam; mud s, Rm Re! ;"j
i - » .
zPlams Infected Bu! m»: Killed Land“: Paints of Inoculation OPomIs o! Soul Slmples m» pH Dalirminlhwl, NW. m:

Fig. 1. Diagram of arrangement of plats in which sulphur was applied
at different rates and to different depths. Locations of plants with root rot
are indicated by areas blocked off, the remaining unmarked portions of rows
indicating normal plants. Points from which soil samples were taken
November, 1932, lettered from left t0 right in each plat.

whether this distribution of root rot was correlated with differences in
pH within these plats. The points at which samples were taken are des-
ignated in Figure 1, along with the distribution of root rot, and the
pH values of the samples are given in detail in Table 17.

These samples showed a surprisingly close relation between the dis-
tribution of root rot in 1932 and the pH. In ﬁve of the six plats in
which samples could be taken from root-rot and root-rot-free areas, the
more acid samples came from the root-rot-free zones. The one exception
was plat 9, in which the root-rot-free zone as well as the root-rot zone
proved to have a surface pH suitable for the disease. It is obvious that
root rot need not necessarily have occurred everywhere that the soil
was favorable.

In the plats in which the comparison can be made, average values
for nine samples from root-rot areas, beginning with the upper soil
layer, were the following: pH 6.4, 5.5, 5.4, 5.6, 6.1, and 7.0. Corre-
sponding averages for 8 samples from root-rot-free areas in these plats
were these: pH 5.75, 5.0, 5.0, 5.4, 5.9, and 6.7. There were thus dif-
ferences at all depths, exceeding 0.5 pH in the upper foot, and amount-
ing to only 0.2 to 0.3 pH in the lower foot and a half. This comparison
would suggest that the acidity of any or all of the soil layers might
have been of signiﬁcance in determining the distribution of root rot in
these plats.

For somewhat more precise comparison, it may be noted that despite

large applications of sulphur in these plats, and the intense acidities
still present in the lower soil layers, root rot spread widely in 1932 in

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT 33

Table 17. Hydrogen-ion concentration 0f soil in individual points in plats
from samples taken November 20, 1932. (Letters designating points
of sampling are the same as those used in Figure 1;
italics indicate samples from root-rot-free areas.)

pH of soil from following depths:
Plat Point of
No. sampling
0-6 6-12 12-18 18-24 24-30 30-36
inches inches inches inches inches inches
1 a 6.8 6.8 6.9 7.1 7.2 7.4
b 7.2 5.8 6.4 6.9 6.9 7.4
c 7.5 7.5 6.6 7.0 7.2 7.5 '
2 a 5.7 6.2 5.8 7.0 7.5 7.9
b 5.4 4.8 4.9 6.1 6.1 6.8
3 a 5.3 4.7 4.5 4.9 5.6 6.9
b 5.8 5.1 4.9 5.3 5.8 7.2
c 6.5 5.8 5.7 5.1 5.9 6.8
4 a 5.3 5.0 5.5 5.8 7.1 7.1
b 6.2 5.4 5.5 5.7 6.0 6.7
c 6.7 6.7 6.2 6.2 6.9 7.4
5 a 5.9 5.2 5.3 5.9 6.8 6.9
b 6.8 6.1 5.4 5.8 6.8 7.2
c 7.2 4.8 5.2 5.7 6.1 7.0
6 a 4.6 4.4 4.2 4.4 4.5 5.0
b 5.4 4.5 4.3 4.3 4.2 5.4
c 5.1 4.7 4.8 4.8 4.7 6.0
7 a 5.4 5.1 6.0 5.8 6.4 7.0
b 4.9 4.3 4.8 5.3 5.9 7.0
c 5.7 5.3 5.8 5.9 6.3 6.7
8 a 6.8 4.1 4.1 4.8 5.5 6.3
b 6.7 4.8 4.9 5.2 6.3 6.6
9 a 6.2 5.3 4.8 4.7 4.9 6.0
b 7.2 4.0 4.0 4.1 4.4 6.8
c 7.2 5.2 4.8 3.9 4.2 5.0
10 a 8.7 8.7 8.4 8.2 8.0 8.0
b 8.5 8.6 .2 7.9 7.8 7.8
Root-rot areas, 14 samples: *
Range Maximum . . . . . . . . .. 7.5 7. 6 9 .1 7 S 7.
Minimum . . . . . . . . .. 5.4 4.0 4 0 4.1 4.4 6.0
Mean . . . . . . . . . . . . . . . . . . .. 6.6 5.6 6 .8 6.3 7.
Root-rot-free, 11 samples:
Range Maximum . . . . . . . . .. 7.2 5. 5.5 6.1 7.1 7.2
Minimum . . . . . . . . .. 4.6 4.3 4.2 3.9 4.2 5.0
Mean . . . . . . . . . . . . . . . . . . .. 5.6 4.8 4.9 .1 5.5 6.4

*Excluding the untreated check area, plat 10.

plats 9, i8, and 5 (excluding the portion of plat 5 around sample 5a).
The soil here obviously allowed root rot to spread and kill many of the
plants. Comparing the pH With that in plats 4 and 6, which remained
free of root rot despite the previous inoculations and the spread dur-
ing this year, it is to be noted that the values here at 6-12 inches, 12-
18 inches, and 18-24 inches averaged almost precisely the same as in
corresponding depths in the root-rot area mentioned. But at 0-6 inches,
the soil in these root-rot-free plats ranged from pH 4.6 to 6.2, averag-
ing 5.3; while the soil in the root-rot area, overlaying equally acid

34 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

subsoil, ranged from pH 6.2 to 7.2, averaging 6.65. It seems reasonable
t0 conclude that the crucial difference between these areas that allowed
root rot to spread in over plats 8, 9, and 5 was probably the loss of the
acidity in the 0-6 inch soil layer.

It is possible that in these plats root rot spread unusually close to
the surface, and that such a condition might be true of the rather’ dense
Lufkin soil in which this experiment was located, but might not occur
in another soil type. Moreover, artiﬁcial irrigation of the plats kept
the soil moist during the growing season and presumably thus raised
the height in the soil at which spread of root rot could occur. The
results of this experiment can therefore be used only with reservations
in making any general conclusions.

Under the conditions of this experiment, encroachment of root rot
into sulphur-treated plats was not prevented by continued acidity of the
deeper soil layers, after the surface soil layer had shifted back toward
neutrality. No conclusions can be drawn from this experiment on
whether the favorable surface soil layer, overlaying a highly acid sub-
soil, would have allowed successful overwintering. Also, no information
is furnished by this particular experiment as to Whether the presence of
a thin acid surface layer of soil would have been enough to reduce or
eliminate root rot in a ﬁeld in which the disease was well established
and in which the deeper soil remained alkaline. Root rot did not be-
come established during the ﬁrst year of this experiment in plat 1, in
which only the ﬁrst six inches of soil had become deﬁnitely acidiﬁed.
This would indicate that spread from the inoculated plants was deﬁ-
nitely impeded by the acidiﬁcation of the surface layer of soil in this
plat. The open question here is whether root rot would similarly have
been impeded had it already been thoroughly established in the favor-
able soil below, prior to the application of the sulphur.

Sulphur Applied at Small Rates to Surface Soil, in Plats in Which
Root Rot was Well Established

This experiment was set up in ﬁeld plats in which root rot had al-
ready become thoroughly established. Sulphur was applied to the sur-
face soil in a small ﬁeld of Lufkin ﬁne sandy loam soil at College
Station. Cotton had been grown in this ﬁeld and inoculated repeatedly
with root rot in 1927 and 1928, so that the disease was quite Well
established prior to 1929, when the sulphur applications were made.’

Commercial ﬁour sulphur (Owl brand) was applied in 1929. It was
spread over the surface of three of the plats and spaded into the plowed
soil. The rates used were based on tests with samples from each plat
to determine the amounts of sulphur needed to change the soil to ap-
proximately pH 5.0. Three other plats were treated with lime, applied
in 1929, 1930, and again in 1932. These treated plats were each 30
feet long and alternated with untreated check plats each 15 feet long.
Cotton was planted each year. It was inoculated artiﬁcially with root

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT 35

rot in 1929, but no further inoculations were made in later years. The
results of this experiment are considered in detail in a separate paper
(2) and will only be summarized here.

Effect of surface applications of sulphur on pH of the soil: Periodic
sampling of the soil showed that the greatest effect from the addition
of sulphur was obtained in the 0-6 inch layer of soil (Table 18). With-

Table 1S. Average hydrogen-ion concentration at different depths in plats
treated with sulphur 0n April 2, 1929. (The ﬁrst set 0f samples
was taken prior to application of the sulphur.)

Interval Mean pH values for the depths speciﬁed
since
Plats Date of sulphur

sampling applied, 0-6 6-12 12-18 18-24 24-36
months inches inch_s inches inches inches

A........... . . . . .. ]an.21, 1929 .. 6.6 6.7 6.3 6.4 6.9
June28,1929 3 4.7 5.9 6.0 6.4 7.1

March 5, 1930 11 5.3 5.8 6.0 6.2 6.6

Feb.18,1931 23 5.8 5.9 5.9 6.2 6.7

Dec. 23,1931 33 5.5 5.7 5.7 5.7 6.0

Oct. 26,1932 43 5.7 5.7 5.9 6.1 6.0

]an.8,1934 57 6.3 6.2 6.3 6.5 6.6

E . . . . . . . . . . . . . . . .. ]an.21,1929 .. 5.9 5.9 6.1 6.4 6.8
June 28, 1929 3 4.6 5.8 6.3 6.7 7.0

March 5, 1930 11 4.7 5.6 6.0 6.1 6.6

Feb. 18, 1931 23 5.5 6.0 5.9 5.9 6.5

Dec. 23,1931 33 5.5 5.7 5.8 5.9 6.0

Oct. 26,1932 43 5.4 5.5 5.8 6.0 6.3

Jan. 8, 1934 57 5.8 6.0 6.2 6.4 6.7

I . . . . . . . . . . . . . . . . .. Jan.21, 1929 .. 6.0 6.5 6.9 7.1 7.2
June 28,1929 3 5.8 6.3 6.6 6.7 6.8

March 5, 1930 11 5.3 6.2 6.5 6.6 7.0

Feb. 18,1931 23 6.4 6.7 6.8 6.9 7.3

Dec. 23,1931 33 6.0 6.1 6.4 6.7 6.9

Oct. 26, 1932 43 5.5 5.6 5.9 6.2 6.6

Jan. 8, 1934 57 6.0 6.1 6.5 6.7’ 6.9

in three months, the soil in two of the treated plats became more acid
than pH 5. There was later a gradual shift back toward neutrality.
The deeper soil layers were not changed so rapidly nor to such a great
extent. The deeper soil became gradually more acid over a period of
two to three years, the greatest acidity at about two feet deep being
reached at the end of this time. Thereafter there was a fairly rapid
shift back toward the original reaction.

Effect of the applications on development and overwintering of root
rot: As may be noted in ‘Table 19, root rot diminished only slightly
in the sulphur plats in the summer following the sulphur applications,
despite the acidity obtained in the surface soil- during that season.
This was presumably because every plant was inoculated with root
rot this year. The disease increased in the check plats and in the
limed plats, instead of decreasing. In 1930 and 1931, root rot decreased
in abundance in the check plats, with unfavorable Weather conditions,
and decreased even more in the sulphur plats. In fact, the disease
seemed about to disappear from the sulphur plats in 1931. The follow-
ing years, however, were more favorable for root rot, and the disease

36 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

Table 19. Summary of eﬂfect of sulphur and lime applications 0n the occur-
rence of Phymatotrichum root rot on cotton plants. (1928 ﬁgures
are for occurrence prior to distribution of sulphur and lime.)

Percentages of plants with root rot
Plats Trt atments

1928 1929 1930 1931 1932 1933

A . . . . . . . . . . . . . Sulphur * . . . . . . . . . . . . 89 71 57 33 64 67
E . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 7O 42 18 70 75
I . . . . . . . . . . . . . . " . . . . . . . . . . . . . . 84 98 48 25 63 97
All sulphur plats. . 89 80 49 25 6/6 80

C. . . . . . . . . . . . . .. Lime T . . . . . . . . . . . . . . 89 81 79 6O 98 92

. . . . . . . . . . . . . . . . . . . . . . . . . . . 99 93 48 85 98 100

K . . . . . . . . . . . . . ” . . . . . . . . . . . . . . 46 89 50 94 92 99

All lime plats . . . . . . . . . 78 88 59 80 96 97

B . . . . . . . . . . . . . Check . . . . . . . . . . . . . . . 100 94 59 19 93 84

D . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 99 9O 38 93 81

F . . . . . . . . . . . . . ” . . . . . . . . . . . . . . , 93 91 53 13 91 99

H . . . . . . . . . . . . . " . . . . . . . . . . . . . . . 77 88 62 77 99 99

J . . . . . . . . . . . . .. ” . . . . . . . . . . . . . . . 92 100 44 80 96 100

L . . . . . . . . . . . . . " . . . . . . . . . . . . . . . O 33 12 71 72 9-1

All check plats . . . . . .. 77 84 53 50 91 93

*Sulphur was applied on April 2, 1929, at the following rates: for plat A, 17.5 lb. 0r at 1,500 lb. a
per acre; for plat E, 11.7 lb. or at 1,000 lb. per acre; and for plat I (which is smaller than plats
A or E) 10.75 lb. or at 1,200 lb. per acre.

TLime was applied at equal rates in plats C, G, and K, as follows: in 1929, hydrated lime at 1 ton
per acre; in 1930, ground limestone at 1,000 lbspper acre; and in 1932, ground limestone at
1,000 lbs. per acre.

increased in all plats, although there was still less root rot in the
sulphur-treated plats than in the other plats.

Inasmuch as root rot became destructive again during these later
years of the experiment, even though still less destructive in the
sulphur plats than in the lime or check plats, this experiment would
not justify any conclusions as to the permanent value of small applica-
tions of sulphur for the partial control of root rot or for its possible
ﬁnal elimination from treated areas.

DISCUSSION

Experiments summarized in this Bulletin and in previous publications
agree in demonstrating that Phymatotrichum root rot is more prevalent
and more destructive, in general, in neutral or alkaline soils. The
natural distribution of the disease Within its range apparently is
determined to a, great extent by the presence or absence of such
favorable soils. Other factors may be of local importance or of seasonal
importance. As has been pointed out (1), Within a uniform soil the
hydrogen-ion concentration ceases to be a limiting factor and the pres-
ence or absence of root rot is controlled by other factors.

In the same Way, soil materials adjusted experimentally to various
hydrogen-ion concentrations Were changed with regard to their suit-
ability for the root-rot fungus. Soil previously unfavorable for the
development of the disease has been made favorable by addition of

RELATION OF SOIL ACIDITY TO COTTON ROOT ROT 37

lime. Soil previously favorable for the disease has been acidiﬁed and
has become unfavorable. Continued prevalence of root rot has been
shown in these experiments to be associated more closely with the ﬁnal
hydrogen-ion concentration of the various soil materials than with
original differences in the soil types.

It is still not known, however, whether the correlation of the
presence and destructiveness of the disease with the favorable soil
reaction is due necessarily directly to the pH of the soil, or is based
instead on some related difference possibly not even produced by the
acidity. Some laboratory work has been done on this problem. It was
found that in soil chambers, in the absence of the host plant, differences
in the growth of the fungus correlated well with the pH of the soil,
and did not correlate so well with concentrations of calcium, potassium,
phosphate, carbonate, sulphate, or nitrate ions added to the soil (6).
While the favorable effect of alkaline substrata may not necessarily be
due directly to the hydrogen-ion concentration, it has not yet been
accounted for in any other way. '

The possibility of changing soils to make them unsuitable for root
rot has been considered in several of the experiments in this Bulletin.
It was found impracticable to acidify calcareous soils with a fairly
high lime content. This excludes most of the areas in which root rot
is most destructive, but still leaves for possible consideration exten-
sive regions in which root rot occurs even though the soils are not
highly calcareous.

Experiments with such less highly calcareous soils indicated that
large applications of sulphur to these soils might cause crop injury,
while at the same time root rot was not quickly eradicated from the
unchanged deeper soil layers. In later experiments, smaller applications
of sulphur were made so that cotton grown here was not damaged. At
the same time, the acidity from these surface applications of sulphur
gradually penetrated the soil to several feet deep and apparently lowered
the losses from root rot.

While root rot was not eradicated in any of the plat experiments,
these results and also some with cotton plants grown in the containers
have emphasized the special importance of the pH of the surface soil
layer in determining the continued prevalence of root rot. Root rot was
apparently eradicated in some of the containers by relatively shallow
surface layers of acid soil, despite favorable alkaline subsoil below.
In the ﬁeld plats, the disease spread in over very acid subsoil at points
where the surface soil remained or became neutral. This has suggested
that further experiments with sulphur for the control of root root
should be planned to determine the possible value of intermittent,
repeated applications of small amounts of sulphur to the surface of
non-calcareous soils.

It' may be well to point out that soil acidiﬁcation for the control
of root rot is still in the experimental stage, and is not recommended
now for practical use even in those non-calcareous soils in which it
may later be found of value.

38 BULLETIN NO. 545, TEXAS AGRICULTURAL EXPERIMENT STATION

SUMDIARY

(1) Cotton plants grown in adjoining containers, ﬁlled with soils
varying naturally in hydrogen-ion concentration, were inoculated
artiﬁcially with root rot, caused by the fungus Phymatotrichum omnivorunz
(Shear) Duggar. Original incidence of root rot following the inoculation,
rate of spread, and overwintering of the disease, were greater in the more
alkaline soils and less in the more acid soils.

(2) Many other experiments were made with cotton plants in
containers of soil materials adjusted to different hydrogen-ion concen-
trations by additions of sulphur, sulphuric acid, calcium sulphate,
ammonium sulphate, lime, or sodium carbonate. Root rot was intro-
duced by artiﬁcial inoculation. In general, only low percentages of
infection or overwintering were obtained in soils more acid than pH
5.0. In slightly acid to neutral soils, of about pH 6.0 to 7.0, high per-
centages of infection were obtained following inoculation, but the
percentages decreased in following years. In alkaline soils of pH 8.0 to
8.5 high percentages of original infection were obtained and the disease
killed large numbers of plants for years thereafter.

(3) The acidity of the surface soil seemed of particular importance.
In some cases, a six to twelve-inch surface layer of acid soil caused
immediate or ﬁnal disappearance of root rot. Acidiﬁcation of the
surface soil to at least pH 5.5 apparently Was necessary to produce
rapid decrease in the prevalence of the disease. With the surface layer
left neutral or somewhat alkaline, even extreme acidiﬁcation of the
deeper soil did not eradicate root rot.

(4) Additions of manure, fertilizers, or of the rarer plant nutrients
(manganese, sulphur, iodine, iron, nickel, copper, and boron) did not
reduce incidence or overwintering of root rot. Additions of sodium car-
bonate made soil alkaline and less favorable for root rot; cotton plants
were more tolerant of such artiﬁcially-produced “alkali soil” than was
the root-rot fungus. A ~

(5) Highly calcareous soils could not be acidiﬁed even by repeated
heavy applications of sulphur. Sulphur applied in relatively large
amounts on less calcareous soils, both in the ﬁeld and in small con-
tainers, acidiﬁed the soil but injured the roots. Sulphur applications
were made in small amounts without injury to cotton plants.

(6) In some small ﬁeld plats of Lufkin ﬁne sandy loam soil, sulphur
was worked in to various depths and root rot introduced by artiﬁcial
inoculation. During the ﬁrst two years of the experiment, root rot
attacked only low percentages of plants in the treated plats. After this
time, the disease spread rapidly in those portions of the plats where
the surface soil layer had shifted back toward neutrality even though
the subsoil had remained acid. ‘

(7) In another test, in ﬁeld plats in which root rot was already

thoroughly established, sulphur was applied in small amounts in the
surface soil only. The soil gradually became acid to depths of more

RELATION OF SOIL ACIDITY TO LOTTON ROOT ROT .3‘)

than two feet, over a period of two to three years, and shifted back
toward neutrality thereafter. Root rot decreased in these plats in the
earlier years of this experiment but became destructive again later.

(8) The experiments summarized in this Bulletin have proved that
soils that are originally acid, or that are made acid by additions of
various chemicals, are less suitable for infection of plants by the root-
rot fungus, and less suitable for continued survival of the fungus
from year to year, than are soils originally neutral to alkaline ortmade
so by chemical additions. Unsuitability of acid soils to the root-rot
fungus is not necessarily due directly to the hydrogen-ion concentra-
tion, but is associated more closely with this factor than with original
differences in the soil types.

(9) Practical application of soil acidiﬁcation to the control of root
rot is still in the experimental stage. It is impracticable to acidify
highly calcareous soils. For non-calcareous soils, further experiments

should be performed to determine the value of repeated surface appli--

cations of small amounts of sulphur.

LITERATURE CITED

1. Collins, E. R., W. V. Black, D. V. Ergle, and P. R. Dawson, 1932. Root-
rot occurrence in relation to chemical characteristics of soil. In
gtzepgg; gtgfg the ﬁfth annual cotton-root-rot conference. Phytopath.

2. Ezekiel, Walter N., and J. F. Fudge. A ﬁeld-plat test of sulphur for the
gradual control of Phymatotrichum root rot. (In prep.)

3. Ezekiel, Walter N., D. C. Neal, Paul R. Dawson, and E. B. Reynolds.
1931. Report of the fourth annual cotton-root-rot conference. Phy-
topath. 21: 957-964. '

4. Ezekiel, Walter N., and J. J. Taubenhaus. 1934. Cotton crop losses from
Phymatotrichum root rot. Journ. Agr. Res. 49: 843-858.

5. Ezekiel, Walter N., J. J. ’l‘aubenhaus, and E. C. Carlyle. 1930. Soil-
reaction effect on Phymatotrichum root rot. Phytopath. 20: 803-815.

6. Ezekiel, Walter N., J. J. Taubenhaus, and J. F. Fudge. 1932. Concentra-
tion of salts and soil reaction as affecting growth of the root-rot
fungus in the soil. (Abst.) Phytopath. 22:9.

7. Fraps, G. S., and E. C. Carlyle. 1929. The basicity of Texas soils. Texas
Agr. Exnt. Sta. Bull. 400. 20 pp.

8. Jordan, H. V., P. R. Dawson, J. J. Skinner, and J. H. Hunter. 1934. The
relation of fertilizers to the control of cotton root rot in Texas.
U. S. Dept. Agr, Tech. Bull. 426. 75 pp.

9. King, C. J., Claude Hope, and E. D. Eaton. 1934. Some microbiological
activities affected in manurial control of cotton root rot. Journ. Agr.
Res. 49: 1093-1107.

10. King, C. J., and H. F. Loomis. 1926. Experiments on the control of
cotton root rot in Arizona. Jour. Agr. Res. 32: 297-310. _ _ _

11. King, C. J., and H. F. Loomis. 1929. Cotton root-rot investigations in
Arizona. Journ. Agr. Res. 39: 199-221. _ _

12. Reynolds, E. B. 1929. The effect of sulphur on yield of certain crops.
Texas Agr. Exp. Sta. Bull. 408. 21 pp. _

13. Taubenhaus, J. J., B. F. Dana, W. N. Ezekiel, W. J. Bach, and J. P.
Lusk. 1929. A method of inoculation for Phymatotrichum root rot
investigations. Phytopath. 19: 167-170. _

14. Taubenhaus, J. J., and Walter N. Ezekiel. 1931. Cotton root-rot and its
control. Texas Agr. Exp. Sta. Bul. 423. 39 pp. _ _ _

15. Taubenhaus, J. J., and Walter N. Ezekiel. 1931. Acid inJury of cotton
roots. Bot. Gaz. 92: 430-435. _ _

16. Taubenhaus, J. J., and W. N. Ezekiel. 1933. Incidence of root rot as
affected by additions of fertilizer and other salts to the soil. In
Texas Agr, Exp. Sta. Ann. Rpt. 46: 80-81. ' _

17. Taubenhaus, J. J., Walter N. Ezekiel, and D. T. Killoiigli. 1928. Relation
of cotton root rot and Fusarium wilt to the acidity and alkalinity
of the soil. Texas Agr. Exp. Sta. Bul. 389. 19 pp.

18. Taubenhaus J. J., and D. T. Killough. 1923. Texas root-rot of cotton and
methods of its control. Texas Agr. Exp. Sta. Bul. 307. 98 pp.