'LIBRARY,
A & M coztscg,

c A a: P U s ' R10-1135-6m
TEXAS AGRICULTURAL EXPERIMENT STATION
//""“ A. B. CONNER, DIRECTOR

COLLEGE STATION, BRAZOS COUNTY, TEXAS

BULLETIN NO. 522 DECEMBER, 1935
f
DIVISION OF Cifigtbszifi?’ f... i B  A R Y _
  A “ma, (‘WW0 o1

. t - 1P Sta?‘
Relatlon of the Occurrence of Cotton ROAM»
Rot t0 the Chemical Composition of Soils

 

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

Soils in which cotton root rot generally occurs and causes much
damage are high in fertility, as indicated by their content of nitro-
gen, phosphoric acid, and potash. They are also high in basicity,
contain considerable quantities of lime, and are alkaline in reaction
and heavy in texture. Soils on which cotton root rot rarely occurs
are generally low in fertility, have a low basicity, are neutral to
slightly acid in reaction, and are light in texture.

Alluvial, or river bottom, soils are usually high in fertility and
basicity, but the disease does not generally occur on these soils.
This indicates the action of inhibitory factors in alluvial soils not
usually operative to the same degree i11 heavy upland _soils.

The chemical composition of local areas of soil containing active
root rot may be almost identical with that of adjacent soils on
which root rot is not present. Chemical composition is simply
one of a number of factors influencing the occurrence and virulence

of the disease.

CONTENTS

Introduction ___________________________ ,_

Analysis of soils

Comparative composition of soils from areas in which root rot causes
high and low degrees of damagecm 1

Composition of soils in four areas as related to cotton crop losses
caused biy root rof __ _

Relation of composition of soil type to the degree of damage caused
by cotton root rot

Phosphoric acid
Nitrogen __-_____g
Potash -- ____
Lime and basicity
pH _____ 1 1-
Composition of some alluvial soi1s_____

The composition of adjacent soils of the same type bearing diseased
and disease-free cotton plants_____

General discussion
Summary
References _

12
15
15
15
15
15
16

17
17
19
20

BULLETIN NO. 522 DECEMBER, 1935

RELATION OF THE OCCURRENCE OF COTTON ROOT ROT
TO THE CHEMICAL COMPOSITION OF SOILS

G. S. FRAPs, CHIEF, DIVISION or CHEMISTRY, AND J. F. FUDGE, CHEMIsT

The plant disease commonly known as cotton root rot, caused by the
fungus Phymatotrichum omnivorum, occurs over a very considerable part
of the southwestern United States, having been found in Texas, New“
Mexico, Arizona, California, Arkansas, and Oklahoma. It has been found
in about 200 counties of Texas (16), including practically all of the State
except the Panhandle and parts of the mountainous country near the
New Mexico line.

Cotton root rot affects not only cotton, but a large variety of other
plants, including flowers, ornamental shrubs, trees, and weeds (17). It
may persist for years on the roots of cotton and other plants which have
not fully decayed (5, 10, 11, 16). Sclerotia, resting-bodies of the fungus,
may be formed, remain dormant for years, and then become active centers
of infection (9, 10, 12, 16). Spores are occasionally formed, but it has
not yet been possible to cause them to infect plants (12, 16).

While cotton root rot is extensively distributed in Texas, the degree of
damage caused by the disease varies in different parts of the State. In
the eastern part of the State, where the soils are sandy and generally low
in lime, the disease occurs only in limited areas and seldom causes much
damage. In the black land areas near the center of the State where the
soils are heavy in texture and calcareous, and in some other areas, the
disease causes great damage. The damage done by root rot in the different
sections of the State varies both with the soil and with the season. In
East Texas there are some areas in which the disease occurs and causes
damage, while in the black land section there are some areas in which
the damage is usually low. The disease does not occur in the Panhandle
of Texas, and causes only limited damage in West Texas in lands under
irrigation, where at times there is some accumulation of soluble salts.

Taubenhaus, Ezekiel, and others (3, 16, 18) have shown that the root
rot fungus grows much better and that the disease is more prevalent in
a neutral or slightly alkaline soil than in an acid soil.

Ezekiel, Taubenhaus, and Fudge (4) found in laboratory studies that
additions of calcium carbonate to acid soils caused greater increases in
growth of the fungus than the same weights of calcium or potassium added
in the form of nitrates, sulfates, or phosphates. It seems probable that
there are other relations between the chemical and physical character;
istics of soils and the degree of damage caused by root rot in them. The
object of the work here presented was to ascertain whether such relations
may exist. It was thought possible that the information secured might
help in finding why the disease causes great damage in some soils and
does not do so in others.

 

6 * BULLETIN NO. 522, TEXAS AGRICULTURAL EXPERIMENT STATION

Analysis of Soils

The soil samples used in the study were selected by members of the
Soil Survey as being typical of the respective soil types in the areas from
which they Were chosen. Total phosphoric acid, total potash, and nitrogen
were determined by the methods already described (6). Active phosphoric
acid and potash are the quantities in parts per million of soil which are
soluble‘ in 0.2 N nitric acid. The quantities of lime, magnesia, and acid-

04am 0cm.
“m” m: 

- n
nu: FLOYD E
v O . 1R2: w    
E  WW w
' v ". , JAC ' ’,
WW 1 I m" y:
WW WWW?
‘WWWWW
G

“WW

 
 
    

      

Fig. 1. Estimated losses from cotton root rot in 1928. The figures give the
estimated reduction in yield of cotton.

soluble potash reported are those dissolved by digestion for 16 hours with

l hot hydrochloric acid of 1.115 specific gravity. Basicity, calculated as per

cent calcium carbonate, represents the acid-consuming power of the
soil (7), and was determined by‘? treating the soil with anexcess of acid
and titrating the excess. The reaction (pH) of the soil Was determined

RELATION OF THE OCCURRENCE OF COTTON ROOT ROT 7

either colorimetrically with a LaMotte Comparator or electrometrically
with a quinhydrone electrode. »

In arriving at the figures for the various constituents, as given in the
several tables, the general modal value for a given soil type, rather than

 
   
  

Texas Agricultural Experiment Station
If}! ti‘ Mllkll CAI-g. 0| TQIII
COLLEGE S TATION. TEXAS

BASICITY Or Sou. AREAS

---- .-

NOTMAPP ED

   

E

Fig. 2. Approximate basicity of Texas soil regions.

an arithmetical average, was used. Some individual samples may vary
considerably from the values given. No attempt was made to weigh the
values by number of samples, comparative area covered by the soil type,
or proportion of the area devoted to the growth of crops which are
susceptible to the root rot disease.

Comparative Composition of Soils from Areas in Which Root Rot Causes
High and Low Degrees of Damage

The decrease in yield of cotton caused by root rot in different sections
of the State, as mapped by Ezekiel and Taubenhaus (2), is shown in
Fig. 1, and may be compared with the basicity of soil areas in Texas as
mapped by Fraps and Carlyle (7), shown in Fig. 2, based upon the general
soil map of Texas soils prepared by Carter (1). A fair relation between

8 BULLETIN NO. 522, TEXAS AGRICULTURAL EXPERIMENT STATION

the basicity of the soil and the occurrence of cotton root rot is apparent.
The resemblance of the two maps might have been closer if the prevalence
of the root rot had been mapped by soil areas instead of by counties as

units, as was done in Fig. 1. A comparison of the two maps shows that

the occurrence of cotton root rot is in general limited in soils with a

 

Phosphoric
Acid Potash
_.i_____ Nitro- _ Mag- Basic- No.
Soil Type gen Acid Llme nesia ity pH 0t
per s0lu- Der per per Sam-
Total Active cent Total uble Active Cent cent cent D168
per p.p.m. per per p.p.m.
cent cent cent
High damage:
Houston clay. . . . . .12 7S .16 1.00 .40 200 13.00 .60 20.00 7.6 28
Houston black clay .08 100 .12 1.00 .40 350 4.00 .50 6.50 7.3 39
Houston clay loam .03 150 .07 .65 .30 100 .70 .30 2.00 7.6 7
Houston loam. . . . .03 30 .10 .80 .30 2S0 .50 .20 2.00 7.2 17
Low damage:
Kirvin fine sandy
loam . . . . . . . . .. .04 15 .05 .55 .10 100 .21 .13 .40 7.0 16
Norfolk fine sandy
loam . . . . . . . . .. .03 25 .04 .45 .10 100 .11 .11 .27 6.7 16
Ruston fine sandy
loam . . . . . . . . .. .03 15 .03 .78 .09 9S .12 .12 .20 6.6 13
Tabor fine sandy
am . . . . . . . . .. .04 6 .05 .60 .25 100 .23 .26 .45 6.8 15
Luf kin fine sandy
loam . . . . . . . . .. .04 20 .06 .75 .15 125 .23 .17 .40 6.5 22
High damage
average . . . . . . .. .05 89 .11 .86 .35 225 4.55 .40 7.12 7.4 91
Low damage
average . . . . . . . . .04 18 .05 .65 .14 104 .18 .14 .34 6.7 82

basicity of less than 1%, while it may be extensive in soils with a
basicity of more than 2%. There are exceptions to this general
relationship.

The sandy soils of East Texas may be taken in a general way to
represent those in Which there is little or no damage by cotton root rot,
while the soils of the Houston series of the black land area may be taken
to represent those in which the damage is high. Table 1 contains a com-
parison of‘ the chemical composition of some soils of the Houston series,
representing the areas in which a high degree of damage is caused by
root rot, and of the Norfolk, Kirvin, Ruston, Tabor, and Lufkin series,
representing the areas in which very little_ damage is caused by the
disease. On an average, the soils in which root rot causes great damage
are higher in total phosphoric acid, active phosphoric acid, total nitrogen,
total potash, acid soluble potash, active potash, lime, and magnesia than
are the soils in which the occurrence of root rot is very limited. The
soils which are favorable to root rot are also high in basicity and tend
to be slightly alkaline in reaction, while the soils which are unfavorable
are neutral or slightly acid in reaction. The favorable soils are heavy
soils, while most of the unfavorable soils are more porous and open.

RELATION OF THE OCCURRENCE OF COTTON ROOT ROT 9

The soils selected for the comparison given are extreme cases. The differ-
ences found may have no connection with the degree of damage caused
by the disease. a

Composition of Soils in Four Areas as Related to Cotton Crop Losses
V Caused by Root Rot

The various areas outlined by Ezekiel and Taubenhaus (2), based
upon reductions in yield of cotton caused by root rot, were taken as a
basis for further study. In Table 2 is given the average chemical com-
position of representative samples of the principal soil types for the four
regions in which most of the cotton grown in Texas is produced. As noted
above, these are averages of modal values for the individual soil types,
not weighed in any way.

The estimated reduction in yield of cotton averaged 6.5% or less in
areas A and C (Table 2) comprising in general the East Texas Timber
Country and the Gulf Coast Prairies. Most of the soils of these areas

Table 1. Comparative composition of surface soils from areas in which root
rot causes high and low degrees of dalnage

Table 2. Approximate average composition of surface soils of principal soil
types of areas of varying cotton crop losses caused by root rot

Re- Phosphoric
Desig- duc- Acid ~ Potash
nation tion Ni-
of Approximate in tro- Mag- Basic.
Area soil area yie :1 gen Acid _ Lime nesia ity pH
in of Total Ac- per Total solu- Ac- per per per
Figure cotton per tive cent per ble tive cent cent cent
per cent ppm. cent per ppm.
cent 1 cent
A East Texas Timber
Country . . . . . . . . .. 0.7 .033 15 .050 .71 .14 110 .10 .17 .35 6.5
C Gulf Coast Prairie... 4.5 .032 38 .078 .78 .17 184 .39 .24 .71 6.5.
D Blackland Prairies. . 12.9 .052 56 .099 .76 .28 207 1.97 .45 3.47 7.0
E Rio Grande Plain... 16.8 .061 53 .091 1.34 .70 456 0.61 .45 _1.34 7.4

are light soils, and principally fine sandy loams. The Lake Charles soils
are the only heavy soils occupying a considerable acreage. Most of the
cotton crop losses, however, occurred on the occasional heavy soils of the
areas. The soils are deficient or low in nitrogen, phosphoric acid,
potash, lime, magnesia, and basicity, and, as a rule, are slightly acid.

The average cotton crop loss was quite high (12.9% and 16.8 %) on the
soils of the Blackland Prairies and tl1e Rio Grande Plain. These soils are
relatively quite high in phosphoric acid, nitrogen, potash, and basicity,
contain considerable limestone, and are heavy in texture and alkaline in
reaction.

The results in general indicate that crops grown in the more fertile soils
are damaged much more by the cotton root rot than are those grown in

the less fertile soils.
The results here reported are not in conflict with the conclusions of

fig’,

. 9/!

10 BULLETIN NO. 522, TEXAS AGRICULTURAL EXPERIMENT STATION

 

Table 3. Relation of chenlieal composition of soil types to the degree of
damage caused by cotton root rot. Upland surface soils
Phosphoric '
cid Potash
Ni- Mag- Basic- N0,
tro- Acid Lime nesia ity pH of
Area and Type Total Ac- gen Total solu- Ac- per per per 3am-
per tive per per ble tive cent cent cent ples
cent ppm. cent cent per ppm.
cent
Blackland Prairies-High
damage:

Bell clay . . . . . . . . . . . . . . .. .08 1S0 . 12 1.10 .45 300 2.40 .90 4.00 7,3 19
Crockett fine sandy 10am. . .03 40 .05 .75 . 11 150 .25 .25 .75 6,4 3
Crockett loam . . . . . . . . . . . .04 30 .09 .62 .20 300 .24 . 16 1 .00 6,4 3

Crockett clay 10am . . . . . . . . 03 10 . 10 . 6O . 12 175 . 35 . 25 . 5O 6. 2 6

Crockett clay . . . . . . . . . . . . .06 8 .14 .75 .40 27S . 60 . 90 1 . 60 7-. 3 2

Houston clay loam . . . . . . . .03 150 .07 .65 .30 100 .70 .30 2,00 7,6 7

Houston loam . . . . . . . . . . . .03 30 . 10 .80 .30 250 .50 .20 2.00 7.2 17

Houston clay . . . . . . . . . . . . .12 75 .16 1.00 .40 200 13.00 .60 20.00 7.6 28

Houston black clay . . . . . . . .08 100 .12 1.00 .40 350 4.00 .50 6.50 7.3 39
Blackland Prairie-Low
damage:
Wilson clay loam . . . . . . . . .04 25 .08 .80 .25 150 ,55 ,35 1,00 7_0 17
Wilson fine sandy loam. . . .03 25 .07 .60 .13 85 ,30 ,15 _50 6_4 10
Wilson clay . . . . . . . . . . . . . .05 20 .08 .60 .25 150 ,80 ,40 1,75 7_() 13
Gulf Coast Prairie-High
damage:
Victoria fine sandy loam. . .04 100 .06 2.00 .25 S00 .50 .30 _75 7,8 12
Lake Charles clay . . . . . . . . .04 20 .12 .70 .30 125 .55 .30 1,25 5,8 26
Gulf Coast Prairie-Medium
damage:
Lake Charles clay loam. . . .03 20 .08 .28 .08 65 .40 .30 .80 6,6 7
Gulf Coast Prairie-Low
damage:
Lake Charles fine sandy
loam . . . . . . . . . . . . . . . .. .02 10 .05 .16 .05 47 .12 .08 .05 5,9 1
East Texas Timber Country
-Low damage:
Bastrop fine sandy loam. . .03 20 .04 1.00 .25 100 .30 .20 1.00 7,2 8
Kirvin fine sandy loam. . . .04 15 .05 .55 .10 100 .21 .13 .40 7,0 16
Lufkin fine sandy loam. . . .04 20 .06 .75 .15 125 .23 .17 .40 6.5 22
Lufkin clay 10am . . . . . . . . . .02 10 .07 .64 .12 90 .30 .15 .25 6,0 5
Tabor fine sandy 10am. . . . .04 6 .05 .60 .25 100 .23 .26 .45 6.8 15
Ruston fine sandy loam. . . .03 15 .03 .78 .09 95 .12 .12 .20 6,6 13
East Texas Timber Country-
No damage:
Norfolk fine sand . . . . . . . . .03 25 .04 .70 .09 90 .12 ,09 ,20 6,5 43
Norfolk fine sandy loam. . .03 25 .04 .45 .10 100 .11 ,11 ,27 6_7 16
Susequehanna clay . . . . . .. g .05 10 .08 .90 .15 150 ,30 ,22 ,,_,, 5_6 5
Susequehanna clay loam. . .02 10 .05 .80 .13 140 .19 .31 .42 6,2 3
Susquehanna fine sandy
loam . . . . . . . . . . . . . . . .. .03 15 .05 .65 14 125 .13 ,11 ,30 6_2 43
RiofGrande Plain-High
damage:
Hidalgo fine sandy 10am.. .05 85 .07 1.15 .58 573 ,99 ,34 1,18 7_7 2
Victoria fine sandy loam. .06 100 .07 1.80 .32 500 .45 .30 1,00 7,6 12
RIoIGrande Plain-Medium '
damage: ‘
Duval fine sandy 10am. . . . .03 20 .06 1.00 .30 200 .30 .20 .30 6.6 12
Victoria clay 10am . . . . . . . .16 *500 .15 1.75 .90 600 .90 .60 1.60 7,4 4
Victoria clay . . . . . . .  . .. .04 25 .13 1 .00 .60 400 .85 . 70 3.50 7.3 11
Webb fine sandy loam. . . . .05 25 .06 1.20 .42 350 .40 .40 .80 7,5 11
RiofiGrande Plain-Low
damage:
Brennan fine sandy loam. . .04 63 . 10 1,50 .80 *550 _5() _61 L00 __~ H 3
Edwards Plateau and Roll-
ing Plains-Medium
damage:
Abilene clay loam . . . . . . .. .06 25 . 16 1 .25 .60 500 1.00 .60 1.05 7. 2 11
Edwards Plateau and Roll-
ing Plains-Low damage:
Miles fine sandy loam. . . . .04‘ 40 .05 1.20 .25 200 .30 .22 .50 7.1 15
Denton clay . . . . . . . . . . . .. .07 25 .15 1.00 .45 150  .60 5.00 7.3 14

*Excluded from averages.

RELATION OF THE OCCURRENCE OF COTTON ROOT ROT

11

N0.
Sam-
ples

(MN >4
OOJQOOUHPDUI

10

wow:

19

16
21

’ Table 4. Relation of chemical composition of soil types to the degree of
damage caused by cotton root rot. Upland subsoils
Phosphoric
Acid Potash
Ni- Mag- Basic-
tro- “ Acid Lime nesia ity pH

Total Ac- gen Total so1u_- Ac- per per per

per tive per per ble tive cent cent cent

cent ppm. cent cent per ppm.

cent
Blackland Prairies-High
damage:

Bell clay . . . . . . . . . . . . . . .. .07 70 .07 1.00 .50 200 2.50 .60 5.00 7.4
Crockett fine sandy loam. . .03 15 .06 .75 .30 1S0 .60 .40 1.25 7.0
Crockett loam . . . . . . . . . .. .04 45 .05 .65 .45 150 1.20 .80 2.50 7.0

Crockett clay loam . . . . . . . .04 10 .07 .85 .40 150 .50 .45 .70 6.3

Houston loam . . . . . . . . . . . .03 12 .06 .80 .27 50 .45 .30 1 . 10 6.5

Houston clay loam . . . . . .. .03 10 .06 .75 .50 150 2.25 .45 4.50 7.6

Houston clay . . . . . . . . . . .. .10 10 .08 1.00 .35 65 20.00 .60 10.00 7.5

Houston black clay . . . . . . . .08 35 .08 .80 .40 150 5.00 .60 5 .00 7.3
Blackland Prairies-Low
damage:
Wilson fine sandy loam. . . .03 15 .06 .65 .25 125 .40 .40 .95 6.6
Wilson clay loam . . . . . . . . .04 15 .07 .08 .25 125 .55 .40 1.25 7.0
Wilson clay . . . . . . . . . . . .. .04 12 .06 .09 .25 125 1.00 .40 1.50 6.8
Gulf Coast Prairies-High
damage:
Victoria fine sandy loam. . .05 100 .06 1.60 .40 275 .45 .35 1.00 7.6
Lake Charles clay . . . . . . .. .03 10 .07 .60 .35 150 .60 .50 1.25 6.5
Gulf Coast Prairie-Medium
damage:
Lake Charles clay 10am. .. .02 15 .04 .25 .12 50 .50 .40 1.00 7.2
Gulf Coast Prairies-Low
damage:
Lake Charles fine sandy
loam . . . . . . . . . . . . . .. .02 9 .04 .20 .07 58 .13 .12 .20 5.9
East Texas Timber Country-
Low damage:
Bastrop fine sandy loam. . .04 10 .05 1.10 .50 200 .50 .40 .60 6.8
Kirvin fine sandy loam. . . .06 10 .05 .65 .30 100 .25 .25 .60 6.4
Lufkin fine sandy loam. . . .03 10 .05 .80 .24 100 .40 .32 .80 6.5
Lufkin clay loam . . . . . . . . . .02 13 .04 .55 .20 85 .35 .25 .60 6.0
Tabor fine sandy loam. . . , .04 7 .04 .60 .25 100 .28 .27 .55 6.8
East Texas Timber Country-
No damage:
Norfolk fine sand . . . . . . .. .02 15 .02 .70 .09 75 .11 .10 .12 6.3
Norfolk fine sandy loam. . .03 10 .04 .80 .15 100 .14 .12 25 6.2
Susequehanna clay . . . . . . . .06 5 .05 .75 .40 250 .25 .48 .55 5 .9
Susequehanna clay 10am. . .03 8 .04 1.30 .18 125 .20 .20 .34 5.8
Susquehanna fine sandy
loam . . . . . . . . . . . . . . . . . .03 9 .04 .88 .24 125 2O .28 .53 6.0
Rio Grande Plain-High
damage:
Hidalgo fine sandy 10am . . . 05 100 . O6 1 .40 . 59 435 3 . 52 . 73 5 . 95 7 . 8
Victoria fine sandy 10am. . .049 100 .05 1.60 .40 350 .53 .30 2.00 7.8
Rio Grande Plain-Medium
damage:
Duval fine sandy 10am. . .. .041 10 .05 1.10 .30 200 .20 .27 .34 7.0
Victoria clay . . . . . . . . . . . . .03 135 . 11 1.40 .65 250 . 87 1.00 3.80 . . . ..
Victoria clay loam . . . . . . . . 12 650 .06 2.00 . 75 400 2.80 .78 7.80 7.5
Rio Grande Plain-Low
damage:
Brennan fine sandy loam. . .03 40 .05 1.80 .57 500 .28 .47 .59 7.5
Edwards Plateau and Roll-
ing Plains-Medium
damage:
Abilene clay loam . . . . . . . . .06 30 .09 1.25 .65 300 4.00 .60 4.50 7.5
Edwards Plateau and Roll-
ing Plains-Low damage:
Denton clay . . . . . . . . . . . . . .06 10 .08 1.00 .50 100 .65 .70 10.00 7.6
Miles fine sandy loam . . .. .04 15 .05 1.40 .50 250 .40 .40 .65 7.3

12 BULLETIN NO. 522, TEXAS AGRICULTURAL EXPERIMENT STATION

Jordan et al. (8) that the use of suitable fertilizers, by acceleration of
maturity, may be a means of evading losses due to progressive killing of
cotton plants by root rot 0n heavily infected fields, or that the increases
in total yield by means of the fertilizers may‘ more than compensate for
losses that would otherwise occur. The work here reported shows that
root rot iS_I1’lOI‘8 destructive on the fertile soils than in the poor soils,
while the work of Jordan shows that the use of fertilizers may result
in producing a larger crop of cotton before the plant is killed by the
disease.

Relation of Composition of Soil Type to the Degree of Damage Caused by
Cotton Root Rot ~

As already stated, within the same area there are great differences in
the damage caused by cotton root rot on different soil types. On some soil
types crop losses may be very great, while on other soil types the damage
is comparatively light. It is somewhat difficult to classify some of the
soil types with respect to the damage caused by root rot, since there is a
variation in the damage caused by the disease in different years.

Information regarding the relative damage caused by root rot on various
soil types within the same general area have been collected from exten-
sive field observations by Dr. J. J. Taubenhaus of the Division of Plant
Pathology and Physiology and Mr. W. T. Carter of the Division of Soil
Survey. They classified the soil types according to whether the disease
caused high, medium, low, or no damage to susceptible plants grown on
the soils. '

The average chemical composition of surface soils (mostly 0-7" in
depth) of these individual types is given in Table 3. Similar analyses for
the subsoils (mostly 7”-19”) are given in Table 4. In these tables, the
soil types are grouped first by the general soil region in which they occur,
and then by the degree of damage caused by cotton root rot on the type
as a whole. Only upland soils are given, for reasons which will be dis-
cussed later. The analyses used are those of typical soils collected by the
field agents of the Bureau of Chemistry and Soils in connection with
their surveys of various counties in Texas.

In considering the data presented, it must be remembered that indi-
vidual samples of a given soil type may differ considerably in composition;
the figures given are those which are considered as approximate modal
values. In the case of most soil types, there may be exceptional local
areas ‘not conforming to the estimate for damage or the values given for
chemical composition. For example, on some areas of the Wilson clay
loam, there is either no damage or it is very small. However, other areas
of Wilson clay loam are known in which the loss in a given year has been
as high as 60 per cent. Individual variations in composition may be
responsible for part of this variation. The areas of Wilson soils on which
high damage occurs are calcareous and have an alkaline reaction, while
Wilson soils on which little damage by root rot occurs are non-calcareous
and have a slightly acid reaction,

RELATION OF THE OCCURRENCE OF COTTON ROOT ROT 13

Table 5. Relation between average chemical composition of soil types and
degree of damage caused by cotton root rot

High Medium 3' Low No
Damage Damage Damage Damage
Total Phosphoric acid, per cent:
Blackland Prairies . . . . . . . . . . . . . . . . . . . . . . . . . . .055 . . . . . . . . . . .045 . . . . . . . . . .

Gulf Coast Prairie . . . . . . . . . . . . . . . . . . . . . . . . . . .040 .030 .020 . . . . . . . . . .

East Texas Timber Country . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .033 .032

Rio Grande Plain . . . . . . . . . . . . . . . . . . . . . . . . . . . .055 .070 .040 . . . . . . . . . .

Edwards Plateau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .060 .055 . . . . . . . . . .

Average of all types . . . . . . . . . . . . . . . . . . . . . . . . . .053 .060 .039 .032

Alluvial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 112
Active Phosphoric acid, parts per million:
Blackland Prairies . . . . . . . . . . . . . . . . . . . . . . . . . . 66 . . . . . . . . . . 23 . . . . . . . . . .

Gulf Coast Prairie . . . . . . . . . . . . . . . . . . . . . . . . . . 60 20 10 . . . . . . . . . .

East Texas Timber Country . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 17

Rio Grande Plain . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 25 63 . . . . . . . . . .

Edwards Plateau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 32 . . . . . . . . . .

Average of all types . . . . . . . . . . . . . . . . . . . . . . . . . 77 24 23 17

Alluvial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1S0 240
Nitrogen, per cent:
' Blackland Prairies . . . . . . . . . . . . . . . . . . . . . . . . . . .106 . . . . . . . . . . .083 . . . . . . . . . .

Gulf Coast Prairie . . . . . . . . . . . . . . . . . . . . . . . . . . . .090 .080 .050 . . . . . . . . . .

East Texas Timber Country . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .050 .052

Rio Grande Plain . . . . . . . . . . . . . . . . . . . . . . . . . . . 070 .100 .100 . . . . . . . . . .

Edwards Plateau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 .100 . . . . . . . . . .

Average of all types . . . . . . . . . . . . . . . . . . . . . . . . . .098 . 108 .069 .052

Alluvial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 . 10
Total Potash, Per cent: ~
Blackland Prairies . . . . . . . . . . . . . . . . . . . . . . . . . . .82 . . . . . . . . . . .67 . . . . . . . . . .

Gulf Coast Prairie . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.35 28 .16 . . . . . . . . . .

East Texas Timber Country . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74 . 70

Rio Grande Plain . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.48 1 .24 1.50 . . . . . . . . .

Edwards Plateau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 .25 1 . 10 . . . . . . . . . .

Average of all types . . . . . . . . . . . . . . . . . . . . . . . . . 1.00 1.07 .79 . 70

Alluvial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.75 2.00
Acid Soluble Potash, per cent:
Blackland Prairies . . . . . . . . . . . . . . . . . . . . . . . . . . .30 . . . . . . . . . . . 21 . . . . . . . . . .

Gulf Coast Prairies . . . . . . . . . . . . . . . . . . . . . . . . . . .28 .08 .05 . . . . . . . . . .

East Texas Timber Country . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16 .12

Rio Grande Plain . . . . . . . . . . . . . . . . . . . . . . . . . . . .45 .55 .80 . . . . . . . . . .

Edwards Plateau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 .35 . . . . . . . . . .

Average of all types . . . . . . . . . . . . . . . . . . . . . . . . . .32 .48 .41 .12

Alluvial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75 . 77
Active Potash, parts per million:
Blackland Prairies . . . . . . . . . . . . . . . . . . . . . . . . . . 233 . . . . . . . . . . 130 . . . . . . . . . .

Gulf Coast Prairie . . . . . . . . . . . . . . . . . . . . . . . . . . 312 65 47 . . . . . . . . . .

East Texas Timber Country . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 121

Rio Grande Plain . . . . . . . . . . . . . . . . . . . . . . . . . . . 535 392 . . . . . . . . . . . . . . . . . . . .

Edwards Plateau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500 175 . . . . . . . . . .

Average of all types . . . . . . . . . . . . . . . . . . . . . . . . . 292 355 116 121

Alluvial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 385
Lime, per cent:
Blackland Prairies . . . . . . . . . . . . . . . . . . . . . . . . . . 2.44 . . . . . . . . . . .55 . . . . . . . . . .

Gulf Coast Prairie . . . . . . . . . . . . . . . . . . . . . . . . . . .53 .40 .12 . . . . . . . . . .

East Texas Timber Country . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23 .17

Rio Grande Plain . . . . . . . . . . . . . . . . . . . . . . . . . . . .72 .61 .50 . . . . . . . . . .

Edwards Plateau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.00 .30 . . . . . . . . . .

Average of all types . . . . . . . . . . . . . . . . . . . . . . . . . 1.89 .64 .33 . 17

Alluvial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . 2.91 2.87
Magnesia, per cent:
Blackland Prairies . . . . . . . . . . . . . . . . . . . . . . . . . . .45 . . . . . . . . . . .30 . . . . . . . . . .

Gulf Coast Prairie . . . . . . . . . . . . . . . . . . . . . . . . . . .30 .30 .08 . . . . . . . . . .

East Texas Timber Country . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 . 17

Rio Grande Plain . . . . . . . . . . . . . . . . . . . . . . . . . . . .32 .48 .61 . . . . . . . . . .

Edwards Plateau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 .41 . . . . . . . . . .

Average of all types . . . . . . . . . . . . . . . . . . . . . . . . . .41 .47 .26 .17

Alluvial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65 .55

14 BULLETIN NO. 522, TEXAS AGRICULTURAL EXPERIMENT STATION

Table 5. Relation between average chemical composition of soil types and
degree of damage caused by cotton root rot (Continued)

High Medium Low No
Damage Damage Damage Damage

Basicity, per cent:

Blackland Prairies . . . . . . . . . . . . . . . . . . . . . . . . . . 4. 26 . . . . . . . . . . 1.08 . . . . . . . . . .

Gulf Coast Prairie . . . . . . . . . . . . . . . . . . . . . . . . . . 1.00 .80 .05 . . . . . . . . . .

East Texas Timber Country . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45 .24

Rio Grande Plain . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.09 1.55 1.00 . . . . . . . . . .

Edwards Plateau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.05 2. 75 . . . . . . . . . .

Average of all types . . . . . . . . . . . . . . . . . . . . . . . . . 3.26 1.34 0.96 .24

Alluvial . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.20 3.35
PH= . .
Blackland Prairies . . . . . . . . . . . . . . . . . . . . . . . . . . 7.0 . . . . . . . . . . 6. 8 . . . . . . . . . .

Gulf Coast Prairie . . . . . . . . . . . . . . . . . . . . . . . . . . 6.8 6.6 5.9 . . . . . . . . . .

East Texas Timber Country . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6. 7 6. 2

Rio Grande Plain . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6 7. 2 . . . . . . . . . . . . . . . . . . . .

Edwards Plateau . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 7.2 . . . . . . . . . .

Average of all types . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 7.0 6. 7 6. 2

Alluvial . . . . . . . . . . . . . . . . . . . . . . . . . . . . .._ . . . . . . . . . . . . . . . . . . . . . . . . .. 7.2 7.4

The analyses presented in Table 3 Were averaged by areas and the
results are presented in Table 5. The analyses for the soil types, as
grouped in Table 3 With respect to degree of damage, Were also averaged
regardless of the area in which they occur, and these averages are given
as “Average of all types.” Values for active phosphoric acid in the

‘ Victoria fine sandy loam and active potash in the Brennan fine sandy

10am were omitted from the averages in Table 5, because they were very
much out of line With the other soil types in the same groups and for the
further reason that, as noted in the last column of Table 3, the number
of samples of these two types was quite small (4 and 2) and their inclu-
sion would have resulted iii an incorrect weighted average. Averages
for alluvial soils (see also Table 7) are given in Table 5, but are not
included in the averages of the upland soil types.

The final averages for each constituent were calculated to relative
values with 100 as the quantity of the constituent in soil in which damage
was high. These results are given in Table 6.

Table 6. Relative average composition of soils on which cotton root rot caused
dificrent degrees of damage

I
High Medium ~ Low No
Damage Damage Damage ' Daliiagg

 

Total phosphoric acid . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 113 73 60
Active phosphoric acid . . . . . . . . . . . . . . . . . . . . . . . . . . 100 31 30 22
Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 110 71 53
Total potash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 107 79 70
Acid-soluble potash. . . . . . . 100 153 128 53
Active potash . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 122 40 41

Lime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 34 17 9

Magnesia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 115 63 41

Basicity . . . . . . . . . . . . . . . . . . . ._ . . . . . . . . . . . . . . . . . . . 100 41 29 8

Reciprocalof H-ion concentration . . . . . . . . . . . . . . .. 100 80 44 14

Average . . . . . . . . . . . . . . . . . . . . . . . . . . .  . . . . 100 91 57 36

RELATION OF THE OCCURRENCE OF COTTON ROOT BOT 15

The data for subsoils are given in Table 4, but they were not sum-
marized and averaged, since they show essentially the same trends as do
the data for the surface soils which are presented in Tables 5 and 6.

In the following discussion of the data presented in Tables 3 to 6 each
element is considered separately.

Phosphoric acid. Total phosphoric acid in groups of soil types on which
the high damage by root rot occurred was about two-thirds greater than
that in the low and no damage groups. Active phosphoric acid was about
three times as great in the high damage group as in the medium damage
and low damage groups, and five times as great as in the group with
no damage.

Nitrogen. Nitrogen in the high damage group was about one-half
higher than that in the 10W damage group, and twice as high as that in
the group without damage.

Potash. Total potash was about one-half greater in the high damage
group than in the no damage group, and one-fourth higher than in the
low damage group. Acid-soluble potash showed considerable variation
in the high, medium, and low damage groups, but the quantity in the
high damage group Was about twice that in the group on which the disease
caused no damage. Active potash in the high damage group was approxi-
mately three times that i11 the low damage and no damage groups.

Lime and Basicity. Lime content and basicity are intimately associated
in soils, since the major part of the basicity of highly basic soils is due to
the presence of calcium carbonate in the soil. Differences in lime content
and basicity were greater than those secured with any other chemical
constituent. Lime and basicity were ten or twelve times greater in the
high damage group than in the no damage group, and several times greater
than in the medium damage and low damage groups.‘

pH. The pH of the different groups does not vary greatly; all groups
have pH values very close to the neutral point (pH 7.0). The pH is a
logarithmic value related to hydrogen ion concentration. When the
hydrogen ion concentrations corresponding to the pH values are used,
differences in the several groups become apparent. The hydrogen ion
concentrations in the loW and no damage groups are considerably higher
than those in the high and medium groups. In the calculation of the
relative concentrations (Table 6), the reciprocal of the hydrogen ion
concentration was used, in order to keep the value of the high root rot
group at 100, as in the other determinations. The relative value of the
reciprocal in the high damage group is about five times that in the no
damage group.

Summary. The data can perhaps best be summarized by the state-
ment that, in general, soils in which a high degree of damage is caused
by root rot are those in which active phosphoric acid, active potash, lime,
basicity, and pH are high. Of these, perhaps the most important are high

lime and high basicity, calcareous soils in almost all cases providing an_

excellent environment for the rapid developmentof the disease.

16 BULLETIN NO. 522, TEXAS AGRICULTURAL EXPERIMENT STATION
Composition of Some Alluvial Soils

Only upland soil types have so far been discussed. Alluvial soils are
soils laid down in the river bottoms, subject to occasional or frequent
overflow with consequent deposition of soil material from all of the soil
areas through which the streams pass, and form a special group of soils

Table 7. Average composition of some important alluvial soil types

Phosphoric
Acid Potash
Ni- Mag- Basic- No.
. tro- Acid Lime nesia ity pH of
Soil Type Total Ac- gen Total solu- Ac- per per per Sam-
- per tive per per ble tive cent cent cent pies
cent ppm. cent cent per ppm.
cent
Surface Soils:
Ochlockonee clay . . . . . . . . .085 70 .140 .80 .33 270 .90 .45 1.70 6.8 6
Ocklockonee silty clay
loam . . . . . . . . . . . . . . . .. .060 34 .055 1.35 .25 12S .74 .48 .35 5.8 6
Ocklockonee fine sandy
loam . . . . . . . . . . . . . . . . . .045 30 .060 .90 .10 130 .18 .14 .50 6.6 99

Trinity clay . . . . . . . . . . . . . . 125 5O . 1S0 1 25 . 60 250 3 . 00 . 75 5 .00 7 . 3 42

Frio clay . . . . . . . . . . . . . .. .150 155 .150 1 35 .80 330 7.50 .85 15.00 7.3 12

Catalpa clay . . . . . . . . . . .. .130 35 .120 1 25 .63 275 4.00 .60 10.00 7.3 16

Frio fine sandy 10am . . . . . . .060 130 .070 1 10 .30 250 .50 .20 85 7.3 11

Frio loam . . . . . . . . . . . . . . . .085 . 200 .110 1 50 .50 430 5.00 .55 9 50 7.4 11
Miller fine sandy loam . . . . .070 200 .060 1 60 .30 250 .30 .25 60 7.3 10
Miller clay . . . . . . . . . . . . . . . 125 125 . 100 2 00 .85 300 5 .00 1 .00 10 00 7 .3 11
Pledger clay. ._ . . . . . . . . . .. .070 250 .080 2 30 1.20 250 3.00 2.50 5 00 7.5 3
Subsoils:

Ocklockonee clay . . . . . . . . .045 25 .080 .75 .30 175 .70 .43 1.30 6.8 7
Ocklockonee silty clay loam .060 34 .055 1 35 25 125 24 48 35 5 . 8 6
Ocklockonee fine sandy

loam . . . . . . . . . . . . . . . . . .040 15 .045 1.00 10 80 .20 . 15 45 6.0 9
Trinity clay . . . . . . . . . . . . . . 125 100 . 150 1 . 25 . 55 250 3 . 00 . 75 5 00 7 . 3 42
Catalpa . . . . . . . . . . . . . . . .. .115 35 . 125 1.25 .55 250 8.00 .75 15 00 7.4 17
Frio clay . . . . . . . . . . . . . . .. .125 35 .095 1.20 .75 150 6.50 .75 12 00 7.5 12
Frio fine sandy loam. . . . . .045 58 .050 1 .25 42 200 1.00 .30 2 00 7.4 16
Frio loam . . . . . . . . . . . . . . . .058 47 .065 0.95 32 290 5.40 .65 9 50 7.6 12
Miller fine sandy loam. . . . .050 50 .045 1.50 47 200 2.50 .40 5 00 7.7 10
Miller clay . . . . . . . . . . . . . . . 100 100 . 070 2 .00 .85 200 5 .00 1.00 10 00 7.5 12
Pledger clay . . . . . . . . . . . . . .070 250 .080 2.30 1.20 250 3.00 2.50 5 00 7.5 3

with respect to damage by cotton root rot. In general, the damage caused
by root rot on alluvial soils is low, although occasional areas occur in
which considerable damage is done. The disease has been artificially
introduced into a typical river bottom soil (19) and reappeared on the
cotton crop of the following year. This indicates that environmental
factors other than the nature and composition of the alluvial soils may
prevent infestation of the soil or inhibit the growth of the organism.
Rea (13) found the sclerotial resting stage of the fungus in alluvial soils
as well as in upland soils. The average composition of a number of
important alluvial soil types is given in Table 7. In general, the soils
are considerably more fertile than the general average of the soils of
the various soil regions in which they occur. Lime, basicity, and pH are
all considerably higher. In so far as the chemical composition of the
alluvial soils is concerned, then, the disease would be expected to do a
great deal of damage on these ‘soils. The fact that it does not do so

RELATION OF THE OCCURRENCE OF COTTON ROOT ROT 17

l

must be attributed to factors other than the chemical composition of the A

soils here discussed.

The Composition of Adjacent Soils of Same Type Bearing Diseased and
Disease-free Cotton Plants

Cotton root rot has a tendency to infect plants in irregular spots sur-
rounding the center of infection. These spots vary considerably in size.
The areas on which plants are not infected may be favorable to the
disease, but the disease may not have progressed far enough to have
reached them. The physical and chemical differences between adjacent
areas on which the plants are diseased or healthy may be insignificant.
In spite of this fact, it was considered desirable to make some analyses
of samples of paired soils from spots bearing diseased and disease-free

Table 8. Comparison of composition of adjacent samples of the same type
bearing diseased (R) and (lisease-free (F) cotton plants of the same type

l

Phosphoric Acid Nitrogen Potash Basicity pH
Total Active Total Active
Depth R F R F R F
in- R F R F per per R F R F per per
ches per per ppm ppm cent cent per per ppm ppm cent cent
cent cent cent cent
Crockett fine sandy
loam . . . . . . . . . . . .. 0- 7 .035 .037 12 1‘3 .062 .082 .41 .37 120 103 .27 .27 6.8 6.1
7-14 037 043 6 6 067 .083 34 37 55 49 .25 .28 6.9 5.9
- 14-24 .044 .043 5 6 .088 .092 .51 .56 91 101 .55 .30 6.1 5.5
Crockett clay loam.. 0- 7 .052 .051 11 17 .148 .111 .61 .81 175 130 1.22 .82 6.1 5.9
7-19 .058 .035 7 7 .087 .069 .80 .72 107 99 1.891.34 7.3 5.9
Lufkin fine sandy loam 0- 7 .040 .043 102 98 .061 .061 .90 .88 235 280 1.14 .33 7.4 7.1
7-19 .016 .013 13 15 .084 .084 .86 .64 147 357 1.36 1.10 7.2 6.4
Wilson fine sandyloam 0- 7 .034 .035 25 34 .132 .123 1.161.18 136 112 .38 .30 6.9 6.4
7-16 019 021 9 9 050 0531 22 1 19 58 51 .14 .18 7.1 6.5
16-24 020 019 5 6 .093 .083 .961.01 107 81 .78 .83 6.7 6.8
Wilson clay loam. . .. 0- 7 .049  8 11 .136 .146 .30 .33 105 105 .901.00 5.8 5.6
7-19 .048 .041 9 6 .114 .079 .34 .31 101 80 1.18 1.17 5.8 5.9
Wilson clay . . . . . . . .. 0- 7 .042 .027 86 14.052 .052 .74 .92 244 131 1.161.18 7.2 6.7
- 7-19 047 024 21 15 049 049 67 67 142 100 1.01 1.41 6.9 6.7

plants. The samples were collected by Dr. J. J. Taubenhaus of the Division
of Plant Pathology and Physiology. Samples of soil from areas on which
plants were infected or uninfected were analyzed. The results are given in
Table 8. Many of the differences between the samples from the two areas
are well within the range of error of the analytical determination. The
reactions (pH) of the root-rot-free areas of the Crockett fine sandy loam
and clay loam and the Wilson fine sandy loam were slightly lower than
those for the infected areas, and may account in part for the absence of
the disease in the uninfected areas. However, they are so nearly neutral
that the slight increase in acidity of the uninfected area could probably
have had comparatively little influence on the control of the disease
(3, 16). This is emphasized by the fact that in the Wilson clay loam,
the most acid soil studied, there was practically no difference in pH
between the area carrying the infected plants and that carrying uninfected

18 BULLETIN NO. 522, TEXAS AGRICULTURAL EXPERIMENT STATION

plants. The active potash in the soil of the infected area of the Wilson
clay is slightly higher than that in the root-rot-free area, but 0n the other
hand that of the root-rot-free area of the Lufkin fine sandy loam is con-
siderably higher than that of the infected area, while there is no significant
difference between the two areas with the other soil types. No other sig-
nificant difference occurred.

The data given in Table 8 emphasize the fact that the chemical co1npo-
sition of the soil is only one of a number of factors which determine the
occurrence and virulence of the cotton root disease. It should be repeated
in this connection that discussion of the relation of chemical composition
of the soil to the damage caused by root rot, as given in this bulletin, is
based upon general, broad relationships and is not applicable to particular
local areas, in which local factors other than the chemical composition
of the soil may determine whether or not the disease causes serious

damage at any particular time.

General Discussion

The preceding work shows that in general a soil which contains appre-
ciable amounts of lime and is slightly alkaline, of good fertility, and a
loam or clay in texture is, in general, favorable to root rot. On the
other hand, a soil which is 10W in lime, slightly acid or acid, and sandy in
character, is unfavorable to the disease.

The extent and rapidity with which the cotton root rot fungus spreads,
its virulence (or the rapidity with which it grows and kills the plant), and
its persistence (or ability to continue over from one season to another),
all vary in different soils and during different seasons. Of the various
factors concerned with differences in the growth of the fungus due to
soil differences, the most important appear to be the pH and basicity as
has already been pointed out (3, 4, 16). Much work has been done on
the relation of the organism to the acidity of the soil (3, 4, 16), and
some of the results obtained indicate that the presence of sufficient
quantities of lime are of more importance to the favorable growth of the
organism than are large quantities of nitrogen, phosphoric acid, or
potash (4).

Variations in the relative damage to plants caused by differences in
soil fertility may perhaps be associated with variations in the chemical
composition of the roots of‘ the plants. Since the root rot fungus feeds
upon the roots, the roots of plants which have been grown in some soils
may be slightly more favorable to the growth of the fungus than they are
when grown in other soils. This is a matter that requires further investi-
gation. Ezekiel, Taubenhaus, and Fudge (5) have shown that extracts
from the roots of monocotyledonous plants (Which are not affected
by cotton root rot) contain substances which inhibit the growth of root rot
and which are apparently absent in extracts from susceptible dicotyledo-
nous plants.

The greater persistence of the cotton root rot in some soils than in
others may be due to several causes. Sclerotia may be produced in

RELATION OF THE OCCURRENCE} OF COTTON ROOT ROT 19

greater numbers in some soils than in others. Some soils, by obstruc-
tion of the access of air to the sclerotia or otherwise, may delay germina-
tion for years, thereby causing the disease to persist for a longer time
than in others. The moisture-holding capacity of heavy soils is much
greater than that of light soils. The moisture may be more favorable
to the growth of the organisms (20) in some soils than in others. The
obstruction of air may hinder the decay of roots, so that they continue
to be a suitable medium for the food of the organism for a longer period
in some soils than in others. The Weeds which serve as hosts may live
better in some soils than in others. These considerations lead to the
conclusion that a favorable root medium may favor the formation of
sclerotia, While ‘the physical character of the soil may be a factor in
preserving the roots, the sclerotia, or the fungus over the winter or for
a longer period.

SUMMARY

Soils of the Houston series, typical of the Blackland prairies, on which
root rot causes a high degree of damage, are higher in total phosphoric
acid, active phosphoric acid, total nitrogen, total potash, acid-soluble
potash, active potash, lime, and magnesia, than are the fine sandy loams of
the Norfolk, Kirvin, Ruston, Tabor, and Lufkin series, typical of the East
Texas Timber Country, on which root rot is very limited. The Houston
soils are also high in basicity and tend to be slightly alkaline in reaction
(pH), While those on which root rot is of slight occurrence are of loW
basicity and are neutral to slightly acid.

Soils of the East Texas Timber Country and the Gulf Coast Prairies,
on which losses of cotton due to root rot were low, are mostly light in
texture, deficient or .loW in phosphoric acid, nitrogen, potash, lime, and
magnesia, low in basicity, and slightly acid in reaction. Soils of the
Blackland Prairies and Rio Grande Plains, on which losses of cotton due
to root rot were high, are chiefly heavy in texture and high in fertility,
as indicated by the content of phosphoric acid, nitrogen, and potash. They
also have a high basicity, contain considerable limestone, and are alkaline
in reaction. '

The principal soil types of Texas were grouped according to the degree
of damage caused by cotton root rot’. On an average, soils on which no
damage was caused by the disease contained only about two-thirds as
much total phosphoric acid, one-half as much nitrogen, total potash, and
magnesia, one-third as much acid soluble potash, one-fifth as much active
phosphoric acid and active potash, one-seventh as much lime and basicity,
and seven times as great a concentration of hydrogen ions in the soil
suspension, as did soils on which damage was high. The average com-
position of soils on which medium and low degrees of damage were
caused by the disease was, in general, intermediate between that of the
soils in the high damage and no damage groups, although several excep-
tions occur.

20 BULLETIN NO. 522, TEXAS AGRICULTURAL EXPERIMENT STATION

Alluvial soils, or soils of river bottoms, were relatively quite high in
fertility and basicity. The 10W damage on these soils must be due t0
other factors Which counteract the high fertility and basicity.

The chemical compositions of adjacent areas of a number of types,
one area of which contained active root rot while the other was free of
the disease, were practically identical, with the possible exception of pH,
indicating that chemical composition is only one of many factors influenc-
ing the occurrence and virulence of the root rot disease.

There is a possibility that chemical composition of the soil may slightly
affect the composition of the roots of the cotton plant so that plants grown
on limestone soils are more susceptible to cotton root rot than are those
grown on non-calcareous sandy soils. The physical or chemical charac-
teristics of the soil may affect the production of sclerotia, their period
of germination, the decay of roots in which the fungus may survive. and

other conditions which affect the over-ivintering of the root rot fungus, ‘

so that clay or loamy limestone soils are more favorable to the carry-over
of the disease than are slightly acid sandy soils.

. REFERENCES

1. Carter, W. T., 1931. The soils of Texas. Texas Agr. Exp. Sta.
Bul. 431.

2. Ezekiel, Walter N., and Taubenhaus, J.‘ J., 1934. Cotton crop losses
from Phymatotrichum root rot. Jour. Agr. Res. 49:843.

3. Ezekiel, Walter N., Taubenhaus, J. J., and Carlyle, E. C., 1930.
Soil-reaction effects on Phymatotrichum root rot. Phytopath. 20:803.

4.~ Ezekiel, W. N., Taubenhaus, J. J., and Fudge, J. F., 1931. Concen-
tration of salts and soil reaction as affecting growth of the root rot
fungus in the soil. Forty-fourth Annual Report, Texas Agr. Exp.
Sta. Also Phytopath. 22:9 (Abst.), 1932.

5. Ezekiel, Walter N., Taubenhaus, J. J., and Fudge, J. F., 1932.
Growth of Phymatotrichum omnivorum in plant juices as correlated
with resistance of plants to root rot. Phytopath. 22:459.

6. Fraps, G. S., 1915-1933. Bulletins on the chemical composition of
the soils of Texas. Texas Agr. Exp. Sta, Buls. 173, 192, 213, 244,
301, 316, 375, 430, 443, 482. _

7. Fraps, G. S., and Carlyle, E. C., 1929. The basicity of Texas soils.
Texas Agr. Exp. Sta. Bul. 400.

8. Jordan, H. V., Dawson, P. R., Skinner, J. J., and Hunter, H. J., 1934.
The relation of fertilizers to the control of cotton root rot in Texas.
U. S. D. A. Tech. Bul. 426.

9. King, C. J., Loomis, H. F., and Hope, Claude, 1931. Studies on
sclerotia and mycelial strands of the cotton root rot fungus. Jour.
Agr. Res. 42:827.

10. McNamara, Homer'C., and‘ Hooton, Dalton R., 1929. Studies of
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RELATION OF THE OCCURRENCE OF COTTON ROOT ROT 21

Neal, David C., and Ratliffe, George T.,1931.
with the cotton root rot fungus Phymatotrichum omnivorum.
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Neal, David C., Wester, R. E., and Gunn, K. C., 1934.
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Jour.

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Forty-sixth annual report, Texas Agr. Exp. Sta.
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Taubenhaus, J. J., Ezekiel, Walter N., and Killough, D. T., 1928.
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Taubenhaus, J. J., Ezekiel, Walter N., and Lusk, J. P., 1931. Pre-
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Taubenhaus, J. J., and Dana, B. F., 1928. The influence of moisture
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Cotton root rot

Recent studies 17