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VII. Specificity in Salt Tolerance

VII. Specificity in Salt Tolerance

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30



H. E. HAYWARD AND C. H. WADLEIGH



trees and ornamental and shade trees. They report a wide variation in

salt tolerance among various members of these groups of crops.

The U. S. Regional Salinity Laboratory has included the problem of

salt tolerance as a major segment of its research program and a number

of lists of salt tolerant plants have been published (Hayward and

Magistad, 1946; Magistad and Christiansen, 1944; U. S. Regional Salinity Laboratory, 1947). I n the most recent publication (U.S. Regional

Salinity Laboratory, 1947), fruit crops, field and truck crops, and forage

crops are classed on the basis of good, moderate, and poor salt tolerance.

The electrical conductivity of the extract of saturated soil is regarded

as the most suitable measurement for appraising soil salinity and its

relation to crop condition and plant growth. On this basis, it would be

expected that an electrical conductivity of the saturation extract equal

to 4 millimhos/cm. (0.1 per cent salt in a medium-textured soil) may

cause significant reduction in growth for plants listed as having poor salt

tolerance. Moderately tolerant crops may do well where the conductivity

does not exceed 8 millimhos/cm., crop growth is restricted if the conductivity is between 8 and 15 millimhos/cm., and no crops and few

species of native halophytes can do well a t conductivities in excess of

that value.

Forage plants, grasses and legumes, as a rule exhibit the highest

degree of salt tolerance on saline lands (Harris, 1920; Kearney and Scofield, 1936; Magistad and Christiansen, 1944), but there are marked

specific differences in this regard. The grasses are more salt resistant

than the legumes, outstanding species being alkali sacaton (Sporobolus

uiroides) , salt grass (Distichlissp&xzta),Nut,tall alkali grass (Puccinellia

Nuttalliana) ,Bermuda grass (CynodonDactylon),Rhodes grass (Chloris

gayuna), and western wheatgrass (Agropyron Smithii) . A number of

other grasses have been reported as having a moderate to high degree of

salt tolerance depending upon other factors. Studies a t Riverside, California, have indicated that the salt tolerance of some grasses is seriously

affected by high soil temperatures, i.e., reed canary grass, perennial ryegrass, meadow fescue and orchard grass (Wadleigh and Gauch *).

Among the leguminous forage plants, alfalfa, white and yellow sweet

clovers, birdsfoot trefoil, strawberry clover, and hubam clover are moderately salt tolerant (Harris, 1920; Kearney and Scofield, 1936; U. s.

Regional Salinity Laboratory, 1947). Ayers (1948) has found that birdsfoot trefoil (Lotus cmiculatus var. TENNUIFOLIUS) has a high salt tolerance and can withstand high summer temperatures. I n salinized plots

irrigated with water containing 5,000 p.p.m. added salts, the relative

yields, expressed as per cent of the yield on the nonsaline control plots,

were: birdsfoot trefoil, 43.6; California Common alfalfa, 40.4; and buf-



PLANT GROWTH ON SALINE AND ALKALI SOILS



31



falo alfalfa, 32.0. Birdsfoot trefoil gave better yields a t medium and

high salt levels (5,000 and 7,500 p.p.m .added salts) than big trefoil,

alsike, red, ladino, and strawberry clovers, in that order.

The data regarding the salt tolerance of strawberry clover appear to

be conflicting. Kearney and Scofield (1936) regarded it as outstanding

and reported satisfactory growth where the salt content of the surface

soil was more than 2 per cent, and Ahi and Powers (1938) rated it as

the most promising resistant legume followed by sweet clover and alfalfa.

On the other hand, Gauch and Magistad (1943) reported that on an

actual yield basis, alfalfa and ladino clover produced 1.3 and 1.9 times

as much forage, respectively, as strawberry clover, and Ayers (1948)

found that it failed to make an appreciable growth a t a high level of

salinity (irrigated with water containing 7,500 p.p.m. added salt). It

seems probable that climatic and soil moisture may account for t.he differences noted above. Strawberry clover appears to be well adapted to

wet, saline pastures and can tolerate high water tables and the cooler

Summer temperatures in the Northwest. The study of varieties of strawberry clover by Gauch and Magistad (1943) illustrates the possibility

of differences in salt tolerance within a species. Five strains were tested

at osmotic pressure of 0.5, 2.5, 3.5, and 4.5 atm. On the basis of actual

yields, significant differences in salt tolerance were observed with respect

to the strains from various sections of western United States.

The salt tolerance of alfalfa, one of the leading forage crops in the

Western States, has been studied extensively (Ahi and Powers, 1938;

Eaton, 1942; Gauch et al., 1943; Harris, 1920; Kearney, 1911;

Kearney and Cameron, 1902; Kearney and Scofield, 1936; and

Magistad e t al., 1943). It has been noted that alfalfa exhibits

differences in salt tolerance during its life cycle being more tolerant

with age (Harris, 1920; Kearney and Scofield, 1936), but there are

few data on the relative tolerance of varieties. Cooil and Brown *

a t the U. S. Salinity Laboratory have tested several varieties using

sand culture and soil plot technics. Six varieties, California Common.

Arizona Chilean, Ranger, Hegazi, Demnat and Tunisia, were tested

in large sand cult.ure tanks at salt concentrations from 0.5 to 6.5 atmowpheres. Based on relative yields, it was evident that there were significant varietal differences in salt tolerance. At the highest salt concentration (6.5 atm.), California Common yielded 77 per cent of t.he control

and Arizona Chilean 72 per cent, whereas Ranger produced only 38 and

Demnat 36 per cent. On an absolute yield basis, California Common,

Hegazi and Arizona Chilean were superior to other varieties tested.

Tests with California Common and Hegazi in salinized soil plots gave



32



11. E. HAYWARD AND C. H. WADLEIGH



consistently higher yields for the latter although relative yields on the

saliniaed plots were higher for California Common.

The cereals are moderately tolerant to salt, and some reports indicate

that they are more tolerant as forage than as grain crops, since the grain

may be inferior when grown under conditions of high salinity (Kearney

and Scofield, 1936; Magistad and Christiansen, 1944). Although reports

differ in regard to the relative tolerance of cereals; barley, rye, wheat and

oats for hay, and barley, rye, oats, rice, wheat and corn for grain have

been listed in that order of tolerance (U. S. Regional Salinity Laboratory, 1947).

There are few data on the salt tolerance of variet,ies of cereals.

Harris and Pittman (1919) tested the salt tolerance of a number of

varieties of oats, wheat, barley and corn, but their experiments were

primarily to determine relative germination and were terminated a t the

end of a 3-weeks growing period. Loughridge (1901) compared Russian

wheats and gluten wheat in field plots a t Tulare, California, and found

that the latter made good growth in soil containing 0.15 per cent salt..

Hayward and Uhvits * found White Federation 38 wheat, to be moderately salt tolerant and fair yields were obtained in sand culture studies

on a saline substrate containing 4 atm. (5,612 p.p.m.) of sodium chloride.

At this concentration, however, t.liere was a reduction of approximately

25 per cent in growth and yield of grain and there was some evidence

that the grain did not fill well when grown on the saline substrates.

Wasatch wheat was used by Reeve e t al. (1948) in leaching studies at

Delta, Utah. They found that yields varied inversely with the residual

salinity of the soil, and that a t low salt levels slight reductions in salt,

content resulted in large increases in yield. For example, a t one site,

(A), reduction in the conductivity of the saturation extract from 40 to

6 millimhos per cm. resulted in an increase in yield from 0.7 to 42.6

bushels per acre.

Recent studies by Ayers and Wadleigh * with eight varieties of barley

indicate a high degree of salt tolerance, and relative yields were not

reduced when the plots were irrigated with water containing 9,000 p.p.m.

added salt. The average conductivity of the saturated soil extracts for

the 0-16 inch depth a t this salinity level was 8.4 millimhos per cm. as

compared with 2.9 millimhos per cm. in the control plots. Corn is t,he

most salt-sensitive cereal and may not produce a satisfactory crop even

on slightly saline soils (Harris, 1920; Kearney and Scofield, 1936). Wadleigh et al. (1947) found Mexican June corn to be less salt tolerant than

alfalfa and more so than beans. Only a few roots penetrated a soil layer

containing 0.2 per cent salt and none were found in the layer where 0.25

per cent salt was added.



PLANT GROWTH ON SALINE AND ALKALI SOILS



33



Root and vegetable crops have a wide variation in salt tolerance

(Harris, 1920; U. S. Regional Salinity Laboratory, 1947). Sugar beets,

table beets, tomato, and asparagus, have shown good to moderate salt

tolerance, but most vegetable crops tested do not appear to be able to

withstand conditions of high salinity (Magistad and Christiansen, 1944).

Beans are very sensitive to salt; and carrots ,onions, lettuce and many

cucurbits have poor to moderate tolerance. Bernstein and Ayers * have

found that lettuce is least affected by given levels of salinity, cantaloupes

are intermediate and beans the most sensitive of these 3 crops. I n each

instance, several varieties were tested and varietal differences were noted

in some groups. With lettuce the relative salt tolerance of 6 variet
was not significantly different with the possible exception of Big Boston

which did not do well. Significant differences were found among varieties

of green beans and Giant Stringless Green Pod, Ranger, and Tendergreen

gave superior yields. Among curcurbits, the Cassaba melon gave higher

relative yields than for cantaloupe, and the cucumber and Conomon

melon were the least salt tolerant.

Sugar beets have good salt tolerance if a stand can be obtained

(Harris, 1920; Kearney and Scofield, 1936; Magistad and Christ.iansen,

1944). The relative sensitivity of this crop in thc germination and seedling stages has been reported in an earlier section. It was pointed out by

Shaw (1905) that (‘ the development of a more alkali-resistant beet

would make i t possible to extend considerably thc area now available

for beet crops.” He found that some beets could withstand salt concentration a t a depth of 2 feet up to 0.43 per cent on a dry soil basis.

Kearney and Scofield (1936) state that rz good stand of beets cannot be

expected if the soil contains more than 0.5 per cent salt. Harris (1920)

eets a lower value if quality is a consideration because increase in salt

concentration decreases yield of sugar. He states that sodium chloride

in excess of 0.04 to 0.05 per cent salt may reduce quality even though

beets will tolerate up to 0.4 per cent. Eaton (1942) using U. S. No. 1

sugar beets reports a high degree of tolerance to chloride, but not to sulfate salts, R greater reduction in yield resulting from 50 m.e./l. of sulfate

than from 150 m.e./l. of chloride addcd to a nutrient solution.

Among the fiber crops, cotton is very salt tolerant (Kearney and

Scofield, 1936; U. S. Regional Salinity Laboratory, 1947), and the long

staple or Egyptian types are more tolerant than the upland types.

Kearney (1911) states that cotton will tolerate 0.4 to 0.6 per cent salt

without injury. Cotton roots can readily penetrate soil containing 0.25

per cent sodium chloride wherc the critical osmotic pressure ranged from

16 t o 17 atm. (Wadleigh et al. 1947). Wadleigh and Gauch * have

studied many varieties of cotton in recent years, using a sand culture



34



H. 1. HAYWARD AND C. H. WADLEIGH



technic and single salts (NaC1, Na2S04 and CaCI2) adjusted to 4.5 atm.

osmotic pressure. All varieties were also grown in well-irrigated and

well-fertilized soil. A summary of yields for 12 varieties over a 3-year

period indicates a marked variation in relative salt tolerance. AmericanEgyptian varieties (SXP, Amsak and Sakel) , Acala 1517 and Acala P-18

have consistently shown a good salt tolerance, Stoneville strains made

very good relative yields on saline cultures but always showed marked

symptoms of salt toxicity. Other strains, Coker 100-6, Deltapine 14 and

Delfos 9252 have not produced well under control conditions a t Riverside, California, and do not. exhibit any marked degree of salt tolerance.

Flax is moderately salt tolerant (Hayward and Spurr, 1944; Kearney,

1911). Kearney and Scofield (1936) report good crops where the salinity

does not exceed 0.4 per cent. Hayward and Spurr (1944) in tests of

Punjab flax in sand cultures under greenhouse conditions found it to be

moderately salt tolerant. The tests were made a t osmotic concentrations

of 1.5 to 4.5 atm. using NaCl, CaClz and Na2S04 as single salts added to

a nutrient substrate. At high concentrations of salt (3.5 and 4.5 atm.)

relative yields of seed were reduced 25 to 62 per cent and no mature seeds

were produced at the highest concentration of sodium sulfate.

Information on the specific salt tolerance of trees and shrubs is

meager. The date palm is perhaps one of the most salt tolerant of all

cultivated plants (Harris, 1920). Magistad and Reitemeier (1943) report

fair growth of dates in the Imperial Valley where the soil solution a t a

moisture content near the wilting percentage contained 15,000 p.p.m. of

salts or an osmotic concentration of 7 atm. Figs, grapes and olives are

moderately salt tolerant, while citrus fruits, apples and pears, and drupaceous fruits are generally regarded as low in salt tolerance (Magistad

and Christiansen, 1944; U. S. Regional Salinity Laboratory, 1947).

Thrifty growth of Persian varieties of grapes has been observed in soils

containing as much as 0.28 per cent salt (Loughridge, 1901). Allison

and Christiansen i t reported good growth of Thompson seedless grapes in

the Coachella Valley, California, when the conductivity of the saturation

extract was as high as 3.5 millimhos/cm. in the second foot of soil. Hayward et al. (1946) report that the Elberta peach is sensitive to moderate

concentrations of salt and state that over a period of years yields can be

expected to decline if t,he salt concentration exceeds two atmospheres.

The Love11 rootstock appeared to be more suitable to moderately saline

conditions than the Shalil. Lilleland et al. (1945) have noted differential

toxicity to sodium in almonds. The Texas variety appears to be more

susceptible than Nonpareil, Ne Plus Ultra and others. Species of citrus

are quite sensitive to salt, especially to sodium chloride (Kelley and



PLANT GROWTH ON SALINE AND ALKALI SOILS



35



Thomas, 1920; Loughridge, 1901). Lemons are the most sensitive and

oranges occupy a position between lemons and grapefruit.

As Eaton (1942) has pointed out, it is difficult and frequently misleading to evaluate the salt tolerance of a species on the basis of appearance. This is especially true of trees and shrubs. There is good evidence

that the effect of saline substrates may be cumulative and that over a

period of years even low concentrations of salt may result in a slow but

progressive decline of a tree crop (Hayward e t al., 1946)

I n summary, two considerations may be stressed with respect to

specificity in salt tolerance. First, it is evident that there are marked

differences in relative salt tolerance among various genera, species and

varieties of agricultural crops. This fact emphasizes the importance of

proper selection of crops for use on lands that are marginal because of

salinity. It suggests also the necessity of furtsher testing and srreening

for salt tolerance on a genetic basis. The second point is that the various

criteria used for appraising salt tolerance may be inadequate if soil

moisture status and other factors are not taken into account.



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New Fertilizers and Fertilizer Practices



.



RANDALL J JONES A N D HOWARD T . ROGERS

Tennessee Valley Authority. Division of Agricultural Relations.

Knoxville. Tennessee

CONTENTS



Page

39



I. Introduction . . . . . . . . . . . . . . . . . . . . . . . .

I1. New and Improved Fertilizer Materials . . . . . . . . . . . . . .

1. Phosphate Fertilizers . . . . . . . . . . . . . . . . . . .

a . Concentrated Superphosphate (40-50 Per cent PnOd . . . . .

b . Defluorinated Phosphates . . . . . . . . . . . . . . .

c. Phosphate Rock-Magnesium Silicate Glass . . . . . . . . .

d . Metaphosphates . . . . . . . . . . . . . . . . . . .

(1) Calcium Metaphosphate . . . . . . . . . . . . .

(2) Potassium Metaphosphate . . . . . . . . . . . . .

2. Phosphorus-Nitrogen Fertilizers . . . . . . . . . . . . . . .

a . Ammonium Phosphates . . . . . . . . . . . . . . . .

b . Dicalcium Nitraphosphate Products . . . . . . . . . . .

c. Ammoniated Superphosphate . . . . . . . . . . . . . .

3 . Nitrogen Fertilizers . . . . . . . . . . . . . . . . . . .

a . Ammonium Nitrate . . . . . . . . . . . . . . . . . .

b . Urea-Form . . . . . . . . . . . . . . . . . . . . .

c. Anhydrous Ammonia . . . . . . . . . . . . . . . . .

4 . Potash Fertilizers . . . . . . . . . . . . . . . . . . . .

5 . Mixed Fertilizers . . . . . . . . . . . . . . . . . . . .

I11. Recent Developments in Fertilizer Use . . . . .

. . . . . . .

1 High Rates of Fertilizer for Corn . . . . . . . . . . . . .

2. Use of Anhydrous Ammonia as a Fertilizer . . . . . . . . . .

3. Methods of Application . . . . . . . . . . . . . . . . . .

a . Furrow-Bottom or “Plow-Sole” Placement of Fertilizers . . . .

b . Subsurface Placement of Fertilizers for Sod Crops . . . . . .

c. Application of Fertilizers in Irrigation Water . . . . . . . .

d . Direct Application of Liquid Fertilizers . . . . . . . . . .

e . Plant-Nutrient Sprays . . . . . . . . . . . . . . . . .

4 . Fertilizing For Winter Grazing in the Southeastern States . . . . .

5 . Miscellaneous Practices . . . . . . . . . . . . . . . . . .

References . . . . . . . . . . . . . . . . . . . . . . .



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I . INTRODUCTION

The estimated fertilizer bill of the American farmer in 1947 was

615 million dollars Fertilizer consumption that year reached a figure of

16.000.000 tons. which was more than double that applied to soils in the



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RANDALL J . JONES A N D HOWARD T. ROGERS



United States in 1939. It is believed that the 1948 figures will be somewhat in excess of those for 1947. Although fertilizer production has increased phenomenally during recent years, the current demand for many

materials still exceeds the supply.

A few years ago the north central region, an area of highly fertile

soils, was not considered to be of great importance from the standpoint

of fertilizer use. Now this is the most rapidly expanding fertilizerconsuming area in the United States, as reported by Mehring (1948). I n

the north central states plant-nutrient consumption increased from



Fig, 1. Increase in



U.S.fertilizer consumption, 1935-1947,by regions,



393,398 tons as an annual average for the 1935-39 period to 779,986 tons

in 1947, or an increase of 303 per cent. Significant increases in fertilizer

use have also occurred in the western states and in the traditionally highfertilizer-consuming Southeast, as illustrated in Fig. 1. With this upward

trend in consumption there has also developed, especially in the Midwest,

a demand for high-analysis materials.

Considerable progress has been made by the chemical engineer and

fertilizer chemist during recent years in the development of new fertilizers

and improvement of processes for fertilizer production. Likewise, the

agronomist, with assistance from specialists in other fields, has found

new ways of using fertilizer which add to its efficiency in crop production

and value for soil improvement,. These recent advancements have a farreaching significance for agricultural development in this country.



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