Advances in agronomy volume 01

ADVANCES IN AGRONOMY
VOLUME I


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ADVANCES IN

AGRONOMY
Prepared under the Auspices of the

AMERICAN
SOCIETY
OF AGRONOMY

VOLUME I
Edited by A. G. NORMAN
Camp Detrick, Prederick, Maryland

ADVISORY BOARD
H. BRADFIELD
H. H. LAUDE
N. P. NEAL

L. A. RICHARDS
V. G. SPRAGUE
E. WINTERS

1949

ACADEMIC PRESS INC., PUBLISHERS

NEW YORK


Copyright 1949, by
ACADEMIC PRESS INC.
125 EAST ,23m STREET
NEW YORK

10,

N. Y.

All Rights Reserved

N o part of this book may be reproduced in any
form, b y photostat, microfilm, or any other means,
without written permission from the publishers.

PRINTED I N THE UNITED STATES OF AMERICA


CONTRIBUTORS
TO VOLUME
I
K. C. BERGER,
Associate Professor of Soils, University of Wisconsin,
Madison, Wisconsin.

FRANCIS
E. CLARK,
Bacteriologist, U . S. Department of Agriculture, Department of Agronomy, Ames, Iowa.
A. S. CRAFTS,
Professor of Botany, University of California, Davis, California.

L. A. DEAN,
Senior Soil Scientist, Division of Soil Management and Irrigation, Bureau of Plant Industry, Beltsville, Maryland.
J. E. GIESEKING,
Professor of Soil Physics, University of Illinois, Urbarn, Illinois.
W. A. HARVEY,
Associate in Botany, University of California, Davis,
California.
H .

E. HAYWARD, Director, U . S. Regional Salinity and Rubidoux Laboratories, Riverside, California.

RANDALL J. JONES,Chief, Soils and Fertilizer Research Section, Division
of Agricultural Relations, Tennessee Valley Authority, Knoxville,
Tennessee.
HovAm T. ROGERS,
Agronomist, Soils and Fertilizer Research Sectiom,
Division of Agricultural Relations, Tennessee Valley Authority,
Knoxville, Tennessee.
ORA SMITH,Professor of Vegetable Crops, Cornell University, Ithaca,
New York.

C. H. WADLEIGH,
Principal Plant Physiologist, U . S. Regional Salinity
and Rubidoux Laboratories, Riverside, California.

MARTING. WEISS,Professor of Farm Crops, Iowa State College, Ames,
Iowa.
WILLIAM
J. WHITE,Oficer-in-Charge, Dominion Forage Crops Laboratory, University of Saskatchewan, Saskatoon, Saskatchewan,
Canada.


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Preface
Many sciences and skills contribute to the subject of agronomy; many
persons with widely different duties can properly call themselves agronomists. Not all of these agronomists would agree as to the precise definition of the word agronomy, yet all, in some way or another, have interests
that relate directly or indirectly to the growth of plants in soil. The
kind of professional training required of those studying the genesis and
classification of soils has few points in common with that required of men
engaged in genetical studies of a particular crop. Yet their fields of
activity are linked by their colleagues who must develop the proper
fertilizer recommendation for profitable production of adapted varieties
of that crop on various soil types.
The great body of knowledge about plants-their nutritive requirements and growth, their management and improvement, their adaptation
and utilization-is continually expanding. It is becoming increasingly
difficult for many of those involved in one way or another in the theory
or practice of soil management and crop production to keep themselves
even reasonably well informed of the newer developments in all but their
immediate fields of activity. Progress is to a degree centrifugal in it.s
effects and through specialization tends to throw us apart.
This volume, Advances in Agronomy, has as its objective the survey
and review of progress in agronomic research and practice. The articles

are written by specialists. They are critical and reasonably comprehensive in treatment. They are written primarily for fellow agronomists
across the hall and across the continents who also find it difficult to keep
well informed in all phases of agronomy. The authors of this volume all
live on the North American continent, and it is primarily North American agronomy that is reviewed. It is not intended that this shall always
be the case, and contributions to latcr volumes will be sought from
workers in other countries overseas.
I n the selection of topics for these volumes an attempt will be made
to include material that will be helpful to workers with diverse subject
matter and regional interests. The edit,ors’ definition of what constitutes
agronomy is catholic; they will be guided in their choice more by what
information may be of use to agronomists than by what constitutes
agronomy. The central theme must be soil-crop relationships, for soils
without crops are barren and field crops cannot be considered without
vii


viii

PREFACE

reference to the soil on which they are produced. From time to time
articles may be included that deal with related fields of horticulture and
forestry. The editors will take cognizance of other publishing plans, in
so far as they are known to them, in order to avoid duplication of
treatment. For example, such considerat,ions led them to omit from this
volume the subject of pastures, which was comprehensively surveyed in
the 1948 Yearbook of Agriculture, and the subject of soil classification
which was reviewed in a recent issue of Soil Science.
The editors wish to acknowledge the co-operation of the several contributors to this volume, whose articles have been prepared as a service
to the profession of agronomy.

A. G. NORMAN

Frederick, Md.
October, 1949.


CONTENTS
Page

Contributors t.o Volume I
Preface., . . . . . .

. . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . .

v
vii

Plant Growth on Saline and Alkali Soils

BY H . E . HAYWARD
AND C . H . WADLEIGH.
U . S. Regional Salinity and Rubidoux
Laboratories. Riverside. California
I. Introduction . . . . . . . . . . . .
I1. Characteristics of Saline and Alkali Soils
I11. Physiological Basis of Salt Tolerance . .

. . . . . .. . . . .

. . . . . . .
. . . . . . .
IV . Physiological Basis of Alkali Tolerance . . . . . . . .
V. How Saline and Alkali Soils Affect Plant Growth . . . .

.
.
.
.
VI . Salt Tolerance as Related to the Life Cycle of the Plant . .
VII . Specificity in Salt Tolerance . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . .

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1
2
5
9
10
20
29

35

New Fertilizers and Fertilizer Practices
BY RANDALL
J . JONES

AND

HOWARD
T . ROGERS.
Tennessee Valley Authority.
Knoxville. Tennessee

I. Introduction . . . . . . . . . . . . .
I1. New and Improved Fertilizer Materials
I11. Recent Developments in Fertilizer Use .
References . . . . . . . . . . . . .

. . . . . . . . . .
. . . . . . . . . . .

. . . . . . . . . . .
. . . . . . . . . .

39
41
53
72

Soybeans
BY

MARTIN
G. WEISS. Iowa State College. Ames. Iowa

.
.

I Introduction . . . . . . . . . . . . . . . . . . . .
. . . 78
I1 Production and Distribution . . . . . . . . . . . . . . . . 80
I11. Disposition and Utilization . . . . . . . . . . . . . . . . . 83
I V . Physiology of the Soybean Plant . . . . . . . . . . . . . . . 85

V. Effect of Climate and Location . . . . . . . . . . . . . . . 97
VI . Effect of Cultural Practices . . . . . . . . . . . . . . . . . 101
VII . Genetics and Cytology . . . . . . . . . . . . . . . . . . . 115
VIII . Variety Improvement . . . . . . . . . . . . . . . . . . . 123
I X . Effect on Soils . . . . . . . . . . . . . . . . . . . . . . 136
X . Disease and Insect Pests . . . . . . . . . . . . . . . . . . 143
XI . The Regional Approach to Soybean Research . . . . . . . . . . 150
References . . . . . . . . . . . . . . . . . . . .
. . 152
I

ix


X

CONTENTS

The Clay Minerals in Soils

HY J . E . GIESEKING.Universil// n j Illinois. lirbnrra. Il1iiini.s
Pagc
I . Introduction . . . . . . . . . . . . . . . . . . . . . . .
159
I1. Historical Developiiicnt ol Clay Mineralogy . . . . . . . . . . 160
I11. Crystal Structure of the Clay Minerals in Soil Clays . . . . . . . 162
IV Qualitative Identification and Quantitative Estimation of the Clay
Minerals . . . . . . . . . . . . . . . . . . . . . . .
171
V Distribution of the Clay Minerals in Soils . . . . . . . . . . . 177

VI . The Configuration of the Clay Mineral Crystals as Related to their
Properties
. . . . . . . . . . . . . . . . . . . . . .
180
VII. The Physicochemical Reactions of the Clay Minerals . . . . . . . 184
VIII . Functions of the Clay Minerals . . . . . . . . . . . . . . . 196
IX. Conclusions . . . . . . . . . . . . . . . . . . . . . . .
199
References
. . . . . . . . . . . . . . . . . . . . . . .
200

.
.

Alfalfa Improvement

BY WILLIAMJ . WHITE.Dominion Forage Crops Laboratory. Univeraily of
Saskatchewan. Saskatoon. ,S%skalchewan. Canada

I . Introduction . . . . . . . . . . . . . . . . . . . . . . .
205
I1. Seed Setting and Production . . . . . . . . . . . . . . . . 206
I11. Progress in Methods of Breeding . . . . . . . . . . . . . . 225
IV. Conquering Some Diseases . . . . . . . . . . . . . . . . . 232
V Summary and Conclusions . . . . . . . . . . . . . . . . . 237
References
. . . . . . . . . . . . . . . . . . . . . . .
238

.

Soil Microorganisms and Plant Roots

BY FRANCIS
E . CLARK.U . S. Department of Agriculture and Iowa Agricultural
Experiment Station. Ames. Zowa
I. Introduction . . . . . . . . . . . . . . . . . . . . . . .
I1. Types of Relationships between Microorganisms and Plant Roots . .
I11. The Rhiaosphere Microflora in Relation to the Growth of Higher Plants
IV . The Numbers of Microorganisms Associated with Plant Roots . . .
V . The Kinds of Microorganisms Found on Plant Roots . . . . . .
VI . Modification of the Root Surface Microflora . . . . . . . . . .
VII . Influences of the Rhizosphere Flora on Succeeding or Associated Plants
. . . . . . . . . . . . . . . . . . . . . . .
References

242
247
249
264
270
274
278
282

Weed Uontrol

.

BY A S. CRAFTSA N D W . A . HARVEY.
University of California. Davis. California
I. Introduction . . . . . . . . . . . . . . . . . . . . . . .
I1 Tillage. Cropping. and Competition in the Control of Weeds . .
I11 Chemical Weed Control . . . . . . . . . . . . . . . . .
IV Principles of Chemical Weed Control . . . . . . . . . . . .

.
.
.

289

. 290
. 293
.

293


xi

CONTENTS

I’agc
V. Herbicidal Action . . . . . . . . . . . . . . . . . . . . .
295
VI . Molecular Properties of Herbicides . . . . . . . . . . . . . . 296
VII . Emulsions and Emulsion Stabilizers . . . . . . . . . . . . . 298
VIII . Selectivity of Herbicides . . . . . . . . . . . . . . . . . . 299

I X . The 2,4-D Herbicides . . . . . . . . . . . . . . . . . . . .
300
X . Uses of 2.4-D . . . . . . . . . . . . . . . . . . . . . .
303
XI . Nitro- and Chloro-substituted Phenols . . . . . . . . . . . . . 307
XII.0ils . . . . . . . . . . . . . . . . . . . . . . . . . .
308
XI11. Other Organic and Inorganic Chemicals . . . . . . . . . . . . 310
XIV . Water Weed Control
. . . . . . . . . . . . . . . . . . 312
XV . Herbicide Application Equipment . . . . . . . . . . . . . . 312
XVI . Drift, Volatilization, Blowing of Herbicides . Secondary and Residual
312
Effects . . . . . . . . . . . . . . . . . . . . . . .
S V I I. Flame Cultivation . . . . . . . . . . . . . . . . . . . .
314
S V I I I. Thc New Agronomy . . . . . . . . . . . . . . . . . . . 314
References
. . . . . . . . . . . . . . . . . . . . . . . 315

Boron in Soils and Crops
BY K . C . BERGER.University of Wisconsin. Madison. Wisconsin

.
.
.

I Introduction . . . . . . . . . . . .
I1 Boron Determination . . . . . . .
111. Boron Availability in Soils . . . . .

IV Boron Requirement of Plants . . . .
V . Summayy . . . . . . . . . . . . .
References
. . . . . . . . . . . .

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321
. . . . . 323
. . . . . 327
. . . . . 336
. . . .
347
. . . .
348

Potato Production

BY OM SMITH.Cornell University. Illmca. New Yolk

. . . . . . . . . . . . . . . . . . . . . . .

I. Introduction
363
I1. Breeding and Improving Potato Varieties
. . . . . . . . . . 355
111. Chemical Weed Control
. . . . . . . . . . . . . . . . . 357
IV . Fertilizer Practices . . . . . . . . . . . . . . . . . . . .
360
V . Rotations and Green Manures . . . . . . . . . . . . . . . . 363
VI . Response to Nitrogen Fertilization . . . . . . . . . . . . . . 365
VII Response to Phosphorus Fertilization . . . . . . . . . . . . . 366
VIII . Response to Potassium Fertilization . . . . . . . . . . . . . . 367
IX. Effects of Magnesium. Liming. and Soil Reaction . . . . . . . . . 369
X . Minor Elements . . . . . . . . . . . . . . . . . . . . .
371
X I Time and Method of Application of Fertilizers . . . . . . . . . 372
XI1 Relation of Yield and Tuber Composition to Plant and Soil Analyses 374
XIII. Killing Potato Vines . . . . . . . . . . . . . . . . . . . 377
XIV. Recent Developments in Insect Control . . . . . . . . . . . . 381
XV Recent Developments in Disease Control . . . . . . . . . . . 385
References
. . . . . . . . . . . . . . . . . . . . . . .
386

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xii

CONTENTS

Fixation of Soil Phosphorus

BY L . A . DEAN.U . S. Department

of Agriculture. Beltsville. Maryland

I. Introduction . . . . . . . . . . . . . . . . . . . . . . .
I1. Accumulation of Phosphorus in Soils . . . . . . . . . . . .
I11. Phosphorus Fixation by Soils. Clay Minerals. and Hydrous Oxides .
IV . Chemically Precipitated Phosphorus . . . . . . . . . . . .
V Fixation of Phosphorus by Surface Reactions . . . . . . . . .
VI . Biological Fixation of Phosphorus in Soils . . . . . . . . . . .
References
. . . . . . . . . . . . . . . . . . . . . . .

.

Author Index

Subject Index

. . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . .

Page
391
. 392
. 393
. 397
. 400
! 406
409

413
436


Plant Growth on Saline and Alkali Soils*
H . E . HAYWARD AND C . H. WADLEIGH
U S. Regionnl Salinity and Rubidoux Laboratories, Riverside. California
C0N TEN TS

I. Introduction . . . . . . . . . . . . . . . . . . . . . . . .
I1. Characteristics of Saline and Alkali Soils . . . . . . . . . . . .
I11. Physiological Basis of Salt Tolerance . . . . . . . . . . . . .
IV . Physiological Basis of Alkali Tolerance . . . . . . . . . . . . .
V . How Saline and Alkali Soils Affect Plant Growth . . . . . . . . .
1. Saline Soils . . . . . . . . . . . . . . . . . . . . . .
a . Sodium . . . . . . . . . . . . . . . . . . . . . .

b.Calcium . . . . . . . . . . . . . . . . . . . . . .
c. Magnesium . . . . . . . . . . . . . . . . . . . . .
d . Potassium . . . . . . . . . . . . . . . . . . . . .
e . Chloride . . . . . . . . . . . . . . . . . . . . . .
f . Sulfate . . . . . . . . . . . . . . . . . . . . . . .
g. Bicarbonate . . . . . . . . . . . . . . . . . . . . .
h.Nitrate . . . . . . . . . . . . . . . . . . . . . .
2. Alkali Soils . . . . . . . . . . . . . . . . . . . . . . .
VI . Salt Tolerance as Related to the Life Cycle of the Plant . . . . . .
1. Germination . . . . . . . . . . . . . . . . . . . . . .
2. Vegetative Growth and Maturation . . . . . . . . . . . .
VII . Specificity in Salt Tolerance . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . .

Page
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15

15
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17

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18
19
19
20
20
25
29
35

I . INTRODUCTION
The yield of a given crop is the net resultant of the effects of the
prevailing weather conditions, the ravages of pathogens, and the existing
status of the soil, within the genetic limitations of the plant . Under
normal conditions, soils affect yield through three primary factors: (a)
moisture availability, (b) nutrient availability, and (c) physical condition . A fourth factor. excess salt.. may be present due to the accumulation of chemical components in the soil that are inhibitive to plant
growth . I n the irrigated soils of arid or semi-arid regions. this factor

* Contribution from the U.S. Regional Salinity and Rubidoux Laboratories.

Bureau of Plant Industry. Soils and Agricultural Engineering. Agricultural Research
Administration. U S . Dept. of Agriculture. Riverside. Calif., in coorperation with the
eleven Western States and the Territory of Hawaii .
1


2

H. E. HAYWARD AND C. H. WADLEIGH

may be a principal consideration on those soils t.hat contain accumulations of salts or alkali.
The problems of plant growth on saline and alkali soils are related
primarily to the irrigated areas west of the Mississippi River. According
to the Bureau of the Census, there were 20,258,191 acres of irrigated land
in this region in 1944. This represents a substantial increase since 1939
of 2,435,228 acres, or 13.7 per cent; and additional areas are coming
under irrigation as a result of new irrigation projects. For example,
about 1,000,000 acres are proposed for development in the Columbia
Basin in the Northwest, approximately 500,000 acres of new land are
being developed in the Lower Colorado Basin, and the proposed development of the Missouri Basin may involve as much as 4,500,000 acres.
Although the soils of some irrigated areas are nonsaline, the accumulation
of salt is a continuing threat to crop production on much of the irrigated
land. The trend in irrigation agriculture is in the direction of using all
the available water including the drainage water and return flow from
older irrigated lands. The increased salt content of such water may be
expected to increase rather than diminish the salt problem.
Owing to the importance of irrigation agriculture in the Western
States and the fact that salt accumulation is a major problem in many
of the irrigated soils of this region, this review is designed to consider
some aspects of plant growth on saline and alkali soils. The classification and composition of saline and alkali soils and their chemical nature

have been reviewed by Magistad (1945). Therefore, t.he consideration
of these topics will be limited to a brief statement of the characteristics
of saline and alkali soils and to definitions of soil terminology as used
by the authors. Four major segments of the plant aspects of the problem
will be reviewed: (a) the physiological basis of salt and alkali tolerance,
(b) how saline and alkali soils affect plant growth, (c) salt tolerance as
related to the life cycle of the plant, and (d) specificity in salt tolerance.

11. CHARACTERISTICS
OF SALINEAND ALEALI SOILS
Saline and alkali soils occur for the most part in regions of arid or
semi-arid climate and the process of salinization is frequently accelerated
by injudicious irrigation and poor drainage. I n arid regions, leaching
and transport of soluble salts to the ocean is not as effective or complete
as in humid regions. Leaching is usually local and the soluble salts may
not be transported far, owing to low rainfall and the high rates of evaporation characteristic of arid climates. On the other hand, water is plentiful during the early development of an irrigation system and there is a
tendency to use it in excess. This may accelerate the rise of the water
table unless provision is made for adequate drainage, and under such


TABLE I
Chemical Composition of Some River Waters Used for Irrigation in
Western United States a

River
Gila
Cobrado
Sacramento
Arkansas
Boise

Rio Grande
Pecos
Sevier
Columbia
Big Horn

Sampling
location

Date
sampled

P.p.m.

Eel06b

Ashurst, Ariz.
Yuma, Ariz.
Tisdale, Calif.
Ldunta, Colo.
Boise, Idaho
Eleph. B., N. Mes.
Comstock, Tex.
Delta, Utah
Wenatchee, Wn.
Thermopolis, Wyo.

4-10-32
3-21-43
2-15-47

7-21-44
11-21-38
6- -46
5- -46
10-17-45
11-29-35
7-29-35

1089
755
73
1000
99
494
2292
1634
116
428

1720
1060
94
1210
133
694
3700
2650
151
612

Ca

Mg

3.59
4.79
0.47
7.18
0.81
28 4
7.63
3 30
0.90

1.99
2.11
03 2
3.49
0.34
1.05
6.78
7.50
0.39
1.19

--

3.08

-

Milliequivalents per liter
Na
€COI

1127
4.06
022
3.47
025
3.00
23.02
1520
0.19
1.96

3.68
2.64
0.73
3.95
0.91
2.67
1.70
4.10
126
2.18

-

“These analyses were made by the U. S. Regional Salinity and Rubidoux Laboratories, Riverside, California.

ECxl06 = conductivity expressed in micromhos per centimeter.
T =trace.

G:

Na,

c1
9.95
2.05
0.09
0.62
0.05
1.10
2333
14.00
0.07
0.76
-

326
639
0.15
9.80
0.32
320
12.44
8.30
021
3.17

-

%

67.0
37.0
21.0

z

242
17.9
43.5
615
578
12.7
31.4

--

E

%

m

&-

3

m

8

E:

w

i


4

H. E. HAYWARD AND C. H. WADLEIGH

conditions ground water may contribute to the salinization of the soil.
This is particularly true if the water applied carries appreciable amounts
of dissolved salts as is frequently the case in irrigated areas. Furthermore, loss of drainage water from irrigated areas upstream and the
pick-up of saline ground water result in more salt downstream. The
range of quality in irrigation waters is shown in Table I which gives t,he
parts per million, electrical conductivity, chemical composition and
sodium percentage for a number of river waters used for irrigation in
western United States.
Although many salt problems are man-made, it should be recognized
that the occurrence of saline and alkali areas is related fundamentally
to changes in climatic conditions, the chemical composition of soil-forming materials in the primary rocks, and to geologic changes that have
taken place with time due to deposition, erosion, weathering and other
processes (Harris, 1920; Hilgard, 1906; de Sigmond, 1938).
There are numerous publications dealing with various aspects of saline

and alkali soils, some of which go back before the turn of the century
(Burgess, 1928; Gardner, 1945; Goss and Griffin, 1897; Hibbard, 1937;
Hilgard, 1886, 1895-1898; Kelley, 1937; Powers, 1946; Tinsley, 1902).
Magistad (1945) has reviewed a number of the schemes of classification
for saline and alkali soils and has reported the terminology proposed for
them. I n view of the differences in the meanings of terms as used in the
literature, the U S . Salinity Laboratory (1947) has published a terminology and description of saline and alkali soils. The terms as defined
in that publication will be followed in this review and are given below:

Alkali Soil-A soil that contains sufficient exchangeable sodium to int.erfere with the growth of most crop plants, either with or without appreciable quantities of soluble salts. (See Saline-Alkali and NomalineAlkali Soil).
Nonsaline-Alkali S o i G A soil which contains sufficient exchangeable
sodium to interfere with the growth of most crop plants and does not
contain appreciable quantities of soluble salts. The exchangeablesodium-percentage is greater than 15, the conductivity of the saturation extract is less than 4 millimhos per centimeter (at 25°C.) and the
pH of the saturated soil usually ranges between 8.5 and 10.
Saline-Alkali Soil-A soil containing sufficient exchangeable sodium to
interfere with the growth of most crop plants and containing appreciable quantities of soluble salts. The exchangeable-sodium-percentage
is greater than 15 and the conductivity of the saturation extract is
greater than 4 millimhos per centimeter (at 25°C.). The pH of the
saturated soil is usually less than 8.5.


5

PLANT GROWTH ON SALINE AND ALKALI SOILS

Saline Soil-A nonalkali soil containing soluble salts in such quantities
that they interefere with the growth of most crop plants. The conductivity of the saturation extract is greater than 4 millimhos per
centimeter (at 25"C.), the exchangeable-sodium-percentage is less than
15, and the pH of the saturated soil is usually less than 8.5.
Alkalization--A process whereby the exchangeable sodium content of

the soil is increased.
Salinization-The process of accumulation of salts in the soil.
Exchangeable-sodium-percentage-This
term indicates the degree of
saturation of the soil exchange complex with sodium and is defined as
follows:
Exchangeable sodium (m.e. per 100 g. soil)
x 100
ESP = Cation exchange capacity (m.e. per 100 g. soil)
Soluble-sodium-percentage-The proportion of sodium ions in solution in
relation to the total cation concentration, defined as follows:

SSP =

Soluble sodium concent.ration (m.e. per liter)
Total salt concentration (m.e. per liter)

x 100

This term is used in connection with irrigation waters and soil extracts.

111. PHYSIOLOGICAL
BASISOF SALTTOLERANCE
Successful agriculture on saline and alkali soils requires the use of
crops capable of producing a sat.isfactory yield under moderate intensities of salt or alkali accumulation. The question arises immediately as
to what constitutes the physiological capacity of a plant to tolerate salt
or alkali. That is, what is salt tolerance and how may it be defined?
The salt tolerance of a variety or a species may be evaluated in three
ways. Firstly, salt tolerance may be looked upon as the capacity to
persist in the presence of increasing degrees of salinity. A given species

may make little or no growth a t the higher levels of salt accumulation,
but i t does survive. That is, power of survival in increasingly saline
soils regardless of growth would be the measure of salt tolerance. This
is largely the criterion of the ecologist in evaluating halophytic environments, since the species most capable of persisting in a saline area becomes the climax vegetation of that area.
Secondly, salt tolerance may be regarded from the standpoint of
productive capacity a t a given level of salinity. For example, a number
of varieties of a given crop may be tested in a soil having a certain degree
of salinization and the highest yielding variety may be designated as the
most salt tolerant. This method of interpretation may give a differen&
evaluation of salt tolerance from the previous one, since experience has


6

H. E. HAYWARD AND C. H. WADLEIGH

shown that the capacity to produce well a t moderate levels of salinity
does not necessarily imply the ability to persist a t higher levels of salt
accumulation. This second criterion is especially useful to the agronomist
in comparing the performance of strains and varieties of a given crop.
Thirdly, the relative performance of a crop a t a given level of soil
salinity as compared to its performance on a comparable nonsaline soil
may be used as a criterion of salt tolerance. This method has certain
advantages over the previously mentioned concepts in that comparisons
between species are more readily evaluated. For example, although preference as to salt tolerance should be given to that variety of alfalfa
having the highest production on saline soil regardless of performance in
the absence of salinity, one could hardly compare salt tolerance in alfalfa
with that in cotton without taking into account the yielding power of
these respective crops when growing on comparable nonsaline soils.
Evaluating salt tolerance on the basis of relative yield will not necessarily result in the same order of classification as power of survival a t

high levels of salinity, but it will provide a more useful basis of appraising agronomic crops to be grown on moderately saline soil. I n variety
and strain testing, tshe data on relative yield should be supplemented by
data on absolute yield; ie., a strain may have a comparably poor relative
yield because of unusual vigor of growth on the nonsaline soil, and yet
yield the best of any of the strains a t the given level of salinity. Everything considered, defining salt tolerance on the basis of relative yield to
that of the nonsaline condition is to be preferred for general agronomic
use.
I n discussing the physiological basis for the various degrees of salt
tolerance which prevail among crop plants, it may be helpful to consider
the characteristics of the natural halophytes. I n a review of this group
of plants, Uphof (1941) discusses the physiological characteristics of
halophytes, but it is apparent that the specific physiology of these plants
is not well known. The early investigators concluded that halophytism
was essentially xerophytism, since both halophytes and xerophytes are
adapted physiologically or anatomically to a scarcity of water. Anatomical studies, such as those of Chermezon (1910), later revealed that
the two groups of plants must be regarded as distinct physiologically.
Halophytes tend to have relatively high values for the osmotic pressure
of the tissue fluids. Fitting (1911) used an indirect method to measure
the osmotic pressure of the cell contents of various species of plants on
the North African Desert. The highest osmotic pressures, 100 atmospheres or above, were found in plants growing on dry or highly saline
soils. Those growing on moist nonsaline soils had osmotic pressures of
10-20 atm. The osmotic pressure of the various species tended to vary


PLANT GROWTH ON SALINE AND ALKALI SOILS

7

with the physiological scarcity of water in the environment in which the
plants were growing. This generalization has been verified by Harris

et al. (1916, 1924), Keller (1920) and others. There may be a wide
variation in the osmotic pressure of the tissue fluids depending on the
environmental stress under which i t is growing. Harris et al. (1924)
found variations in the osmotic pressure of the tissue fluids of leaves of
Atriplex confertifolia from 31.2 to 153 atm. ; in Allenrolfeu occidentalis
from 22.5 to 61.8 atm.; in Sarcobatus vermiculatus from 22.7 to 39.8 atm.;
and in Salicornia utahensis from 36.8 to 51.9 atm.
'Much of the variation in osmotic pressure of the tissue fluids was
found to be associated with variations in chloride content, but not all of
it. Keller (1925) observed that some halophytes may regulate the salt
content of their tissue fluids somewhat independently of the salinity of
the environment-. Salicornia may contain a lower concentration of
sodium chloride than exists in the soil, or i t may accumulate NaCl far
above the concentration of the soil, depending on the degree of soil
salinity. Iljin (1922, 1932) states that only those plants should be considered halophytes whose protoplasm is resistant to relatively high accumulations of sodium ions in the cell sap. Thus, halophytes may be
described as having a t least three attributes which are important to
their survival on saline soil; (a) the capacity to develop rather high
osmotic pressures of the tissue fluids in counteraction to the increased
osmotic pressure of the substrate; (b) the capacity to accumulate considerable quantities of salts in the tissue fluids and to regulate that
accumulation; and (c) a protoplasm which is characteristically resistant
to the deleterious effects of accumulations of sodium salts in the cell sap.
Application of the above criteria to an evaluation of the relative salt
tolerance of economic crops is not sharply defined, and the varying
physiological responses of different crop plants to saline soils prevent any
generalization. Brown and Cooil a t the U.S. Regional Salinity Laboratory found in 1947 that the osmotic pressures of the tissue fluids of alfalfa
tops were 12.3, 14.5, 17.9, and 19.9 atm. when grown on artificially
salinized soils in which the average osmotic pressures of the soil solutions
were 0.9, 4.2, 6.6, and 8.2 atm. respectively. Thus, even though there
was but little variation in the net osmotic gradient between soil and
plant tops, there were marked reductions in yield. If the yield on the

control plot that had 0.9 atm. osmotic pressure in the soil solution be
taken as 100 per cent, the yields on the other plots were 62.5, 32.4, and
21.5 per cent respectively. That is, the marked reduction in yield did.
not reflect the relative constancy in osmotic gradient. The increase in
osmotic pressure of the tissue fluids of the tops of these alfalfa plants
could be largely accounted for by the increase in chloride salts in the


8

H. E. HAYWARD AND C. H. WADLEIGH

tissue fluids. Alfalfa is regarded as one of thc more salt tolerant crops,
and the theory could he advanced that its salt tolerance is related to thc
intake of salt and the resiiltant increase in osmotic pressure of the tissue
fluids as the salinity of the soil is increased. Such a theory could not
be applied to certain other forage crops.
Ayers and Kolisch * determined the osmotic pressure of the expressed
sap of seven different leguminous forage plants grown on soil irrigated
with water containing 0, 2500, 5000, and 7500 p.p.m. of added salts.
Observations on red clover, Trifolium pratense, harvested in July showed
osmotic pressures of the expressed sap of 11.5, 20.6, and 23.7 atm. respectively, for the first t.hree treatments. The most saline irrigation
water, 7500 p.p.m., killed the plants. By August, the plants irrigated
with water containing 5000 p.p.m. of salt were killed, and by September
only one or two plants survived that were irrigated with water containing
2500 p.p.m. added salts. All control plants survived but they did not
thrive during the hottest part of the summer. Thus, red clover showed
very poor salt tolerance, yet the increase in the osmotic pressure of the
tissue fluids for a given increase in salinity of the substrate was greater
than that observed for alfalfa. This suggests that capacity to adjust

internal osmotic pressure with respect to the substrate may be a poor
criterion of salt tolerance. It is pertinent to note that for comparable
levels of salinization, the expressed sap of red clover contained nearly
three times as much chloride as that of alfalfa. It,appears that red clover
plants were capable of effecting internal osmotic adjustments to compensate for the external increase in salinity, but the protoplasm of these
plants was not sufficiently resistant to the deleterious effects of the ions
so accumulated.
I n this connection, the observations of Ayers and Kolisch * on two
species of trefoil are of interest. The osmotic pressure of the expressed
sap of the herbage of birdsfoot trefoil, Lotus corniculatus var. TENNUIFOLIUS, which is a very salt tolerant legume (Ayers, 1948) was 12.0, 16.6,
17.3, and 19.1 atm. respectively for the same qualities of irrigation water
used on red clover. Comparable values for big trefoil, Lotus uliginosus,
were 10.6, 16.9, 18.4, and 21.9 atm. osmotic pressure. There was a greater
internal adjustment in osmotic pressure over a range of soil salinization
in big trefoil than in birdsfoot t.refoil, yet the big trefoil showed relatively
poor salt tolerance. At a given level of salinity, however, the expressed
sap of the herbage of big trefoil contained nearly twice as much chloride
as did the birdsfoot trefoil.
*This, and subsequent references in which the author’s name is followed by an
asterisk, relate to unpublished data obtained at the US. Regional Salinity Laboratory.


PLANT GROWTH ON SALINE AND ALKALI SOlLS

9

Additional evidence available on other economic crops (see below)
indicates t.hat the salt tolerance of a given species depends upon three
attributes: ( a ) the capacity to increase the osmotic pressure of the tissue
fluids to compensate for increases in osmotic pressure of the substrate;

(b) the capacit,y to regulate the intake of ions so as to bring about the
increase in osmotic pressure and yet avoid an excess accumulation of
ions, and (c) the inherent ability of the protoplasm to resist deleterious
effects of accumulated ions. These are the same three attributes that
were stipulated as essential for halophytism. It is apparent that the
main deficiencies of economic crops which lack salt tolerance are the
inabi1it.y to regulate adequately the intake of salt and the specific sensitivity of their protoplasm to accumulations of salt within the tissues.

IV. PHYSIOLOGICAL
BASISOF ALKALITOLERANCE
Very little is known concerning the physiological basis for the tolerance of plants to alkali soils. There appears to be considerable variat*ion
among halophytes as to their tolerance to alkali as contrasted with salinity. Hilgard (1906) points out that Allenrolfea occidentalis and Salicornia subterminalis are two of the most salt tolerant halophtes, but their
tolerance to “black alkali” (alkali) is relatively poor. On the other
hand, Sarcobatus vermiculatus and Sporobolus airoides are also highly
salt tolerant, and have a remarkably high tolerance of “black alkali.”
I n evaluating tolerance of plants to alkali soils distinction must be
made as to whether the soil is (a) high in exchangeable sodium but having a moderate pH, (b) high in exchangeable sodium, but with a pH
of 8.5 or above, and (c) high in exchangeable sodium but with a considerable accumulation of titrat,able carbonate. The latter condition represents the status in “black alkali” soils as described by Hilgard (1906).
Although concrete evidence is very meager, it may be inferred that
tolerance of a species to high percentages of adsorbed sodium is modified
by the pH of the soil and the accumulation of soluble carbonate.
Breazeale (1927) concluded from his studies, however, that sodium carbonate occurs in “black alkali” soils in insufficient concentration to be
toxic. Thus, the infertility of most of these soils must be sought in their
poor permeability to water and to other nutritional disturbances.
Ratner (1935, 1944) presents evidence that plant growth is inhibited
on high-sodium soils owing to availability of calcium. Hence, tolerance
to soil alkali may involve the capacity by the plant to secure an adequate
supply of calcium under conditions of relatively low availability. Bower
and Wadleigh (1948) studied the influence of various levels of exchangeable sodium upon growt,h and cationic accumulation by dwarf red kidney
beans, garden beets and Rhodes and Dallis grasses under controlled cul-

10

H. E. HAYWARD AND C. 13. WADLEIGH

tural conditions in the greenhouse. The culture media consisted of a
mixture of sand and synthetic cation- and anion-exchange resins (“Amberlites”) containing the desired amounts of various cations and anions
in adsorbed form. Adsorbed K, H2P04,NOs and SOr were supplied in
constant amounts to all cultures, the potassium making up 10 per cent
of the cation exchange capacity. Six levels of exchangeable sodium, wiz.,
0, 15, 30, 45, 60, and 75 per cent of the cation exchange capacity, constituted the treatments. The remainder of the cation exchange capacity
was satisfied by calcium and magnesium, the Ca:Mg ratio being 3 : l .
The p H value of all cultures was approximately 6.5.
The tolerance of the different species to the presence of exchangeable
sodium in the substrate varied greatly. Beans were found to be especially sodium-sensitive. Growth of this species was markedly decreased a t
exchangeable-sodium-percentages as low as 15 and almost completely
inhibited a t the three highest levels of sodium employed. I n sharp contrast with the data for beans, Rhodes grass and garden beets were found
to be very sodium-tolerant. Significant reductions in the growth of these
species occurred only a t the highest level of sodium. The growth of
Dallis grass was not significantly lowered a t exchangeable-sodium-percentages of 30 or less but a t the higher sodium levels practically no
growth was obtained.
The Ca, Mg, K, and Na contents of the roots and tops of each species
were determined after harvest. Accumulation of Ca, Mg, and K by the
plants as a whole tended to decrease and that of sodium to increase
progressively as higher proportions of exchangeable sodium were supplied.
The magnitude of the decreases in Ca, Mg, and K accumulation and the
extent of sodium accumulations varied greatly among the species studied
and between the roots and top parts of the plant. These observations
suggest the possibility that the species that are more tolerant to high

levels of exchangeable sodium are the ones which normally take in considerable amounts of sodium, whereas the more sensitive species are the
ones which normally tend to exclude sodium.

V. How SALINEAND ALKALISOILSAFFECTPLANT
GROWTH
Saline soils may affect plant. growth in two distinct ways: (a) the
increased osmotic pressure of the soil solution effects an accompanying
decrease in the physiological availability of water to the plant; and (b)
t.he concentrated soil solution may be conducive to the accumulation of
toxic quantities of various ions within the plant. Alkali soils may possess
three attributes, any one of which may seriously inhibit or entirely prevent plant growth: (a) the relatively high percentage of adsorbed alkali
cations on the exchange complex of these soils may effectively depress


PLANT GROWTH ON SALINE AND ALKALI SOILS

11

the availability of calcium and magnesium; (b) the activity of thc
hydroxyl ion may be sufficiently high to be toxic per se to the plant; and
(c) an accumulation of adsorbed Na on the exchange complex may have
a dispersive effect on the soil, and thereby bring about a “puddled”
condition which may seriously curtail permeability to water and air.
1. Saline Soils

Most evidence indicates that accumulations of neutral salts in the
substrate inhibit plant growth primarily as a consequence of the increase
in osmotic pressure of the soil solution and the accompanying decrease
in the physiological availability of water. Magistad et al. (1943)
studied the growth response of numerous crops in sand cultures in which

relatively large quantities of chloride and sulfate salts were added to a
control nutrient solution. Growth inhibition accompanying increasing
concentrations of added salts was virtually linear with increase in osmotic
pressure, and was largely independent of whether the added salts were
chlorides or sulfates. The slope of the negative regressions of yield on
osmotic pressure of the substrate varied with the salt tolerance of a given
crop. The experiment was carried on under three different climatic conditions, and it was found that the slope of the regressions of yield on osmotic
pressure for a given crop varied with climate. Gauch and Wadleigh
(1944) studied the growth response of beans to increasing concentrations
of NaC1, CaC12, Na2S04,MgC12, and MgS04 added to a control nutrient
solution. Growth depression was linear with respect to the osmotic pressure of the substrate and independent of whether a given level of osmotic
pressure was developed by NaCl, CaC12, or Na2S04. Magnesium salts
had a toxic effect in addition to that which might be attributed to osmotic
pressure.
Hayward and Spurr (1943) attached potometers to corn roots and
measured the rate of entry of water into the roots as conditioned by the
osmotic pressure of the substrate. They found that for a given location
on the root, the rate of entry was inversely proportional to the osmotic
pressure of the substrate and virtually independent of whether the increased osmotic pressure was developed by NaCl, CaC12,Na2S04,sucrose,
or mannitol. Entry of water ceased when the osmotic pressure of the
substrate was maintained a t 6.8 atm.; in fact, a small outward movement
of water was recorded. Significantly, an osmotic pressure of the tissue
fluids of 5.7 atm. was recorded for roots comparable to the ones studied
potometrically. Roots which were permitted to become at least partially
adjusted to a given saline substrate had a higher rate of entry of water
than comparable roots which were not subjected to a preconditioning
treatment prior to the observation period (Hayward and Spurr, 1943).


12

H. E. HAYWARD AND C. H. WADLEIGH

Eaton (1941) and Long (1943) using divided root systems have also
shown that the rate of entry of water into roots is inversely proportional
to the physiological availability of the water as mensiired by the osmotic
pressure of the nutrient solution.
The evaluation of plant response to salinized sand or water cultures
behavior on
is relatively simple as compared to the appraisal of growth
saliniaed soils. The osmotic pressure of the
artificial substrate may
be controlled r a t h e r
precisely, but such control is not possible in a
salinized soil. The osmotic pressure of the
soil solution at a given
salt content of the soil
will vary inversely with
changes in the moisture
c o n t e n t of the soil.
That is, the normal
fluctuation in soil moisture content between
rains or irrigations is
a c c o m p a n i e d by inverse fluctuations in
osmotic pressure of the
soil solution. Also, water cannot move into
or through a soil without carrying solute
PERCENT SOIL MOISTURE
(DRY BASIS)
with it. Consequently,

Fig. 1. Relationship between soil moisture stress and marked variations in
moisture percentage with the salt content at different Q the salt contentof the
values in a sample of Panoche loam.
soil may occur within
the root zone as a result of water movement (Wadleigh and Fireman,
1948). Furt,her, the withholding of water from the plant through surface force action by the soil varies with the moisture content of the soil,
and the effect of this retentive force is theoretically additive to that of
physiological unavailability of water induced by the osmotic pressure of
the soil solution. Wadleigh (1946) has discussed the complexities cont.ributed by these variables in determining the relationship between salt
content of soil and plant response.