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VI. Salt Tolerance as Related to the Life Cycle of the Plant

VI. Salt Tolerance as Related to the Life Cycle of the Plant

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PLANT GROWTH ON SALINE AND ALKALI SOILS



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conclusions were reached by Slosson and Buffum (1898) and Stewart

(1898). They found that if the osmotic pressure was high enough, no

germination occurred ; but it was noted that at a given salt concentration

various species of agricultural plants exhibited differential salt tolerance

with respect to germination. Stewart (1898) found that the cereals as

a group were more tolerant of salt than the legumes, and listed their

relative salt tolerance in the following descending order, barley, rye,

wheat, oats. His order of tolerance for legumes was peas, red clover,

alfalfa, and white clover.

Early investigators tested a large number of agricultural crops to

determine the limits within which seeds would germinate; but, in many

instances, the methods used were not standardized and comparison of

data is impossible. Harris (1915) has reviewed the early literature on

seed germination which was done chiefly in solution cultures, in many

cases using single salts. He points out that. conclusions drawn from such

studies “should not be too definitely applied to the action of alkali as

it is found in the soil,” citing as an example that “the salts of magnesium

when present alone are very toxic, while if added to a normal soil they

are no more toxic than a number of other salts.”

I n his first germination tests, Harris (1915) used glass tumblers which

held about 200 g. of soil. The salt levels ranged from no salt to 10,000

p.p.m., or 1 per cent on a dry weight basis; various single salts and combinations of salts were used and over 18,000 determinations were reported. Like earlier workers, he found that crops varied greatly in their

relative resistance to alkali salts and listed crops tested in the following

descending order of tolerance, barley, oats, wheat, alfalfa, sugar beets,

corn, Canada field peas.

Shive (1916) using a sand culture technic and single salts tested the

germination of beans and corn at osmotic pressures ranging from 0.5 to

8.0 atm. His data indicate that “retarded germination is directly related

to the amount of water absorbed by the seeds, which in turn is dependent upon the concentration of the soil solut.ions.” Rudolfs (1925) tested

seeds of white lupine, watermelon, Canada field peas, buckwheat, soybeans, wheat, corn, beans, alfalfa, and dwarf rape. He used presoaked

seeds and subsequent germination on beds of filter paper with single salts,

NaNOs, Ca

NaC1, K2C03, KCl and MgS04, a t osmotic pressures

up to 7 atm. Except for some of the weaker solutions, absorption, germination, and root-growth decreased with increase in concentration of the

salts. Peas, alfalfa, lupine, buckwheat and watermelon were far less salt

tolerant than corn and wheat.

It is difficult to evaluate the level of salinity conditioning the germination of seeds under field conditions since the amount of soil moisture



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H. E.



HAYWARD AND C. H. WADLEIGH



and the salt conccntration adjacent to the seed are continually changing,

owing to evaporation, capillary transmission, and rainfall or irrigation.

Ayers and Hayward (1948) have reported a method for measuring the

effects of. soil salinity on germination which involves moistening and

salinizing nonsaline soil so that a specified soil moisture percentage and

salinity level are obtained. The moisture content of the soil and the salt

content of the extract from the saturated soil are determined on subsamples and these data permit a calculation of the osmotic pressure of

the soil solution in the germination culture. Weighed amounts of the

preconditioned soil are placed in large culture dishes and planted with

a definite number of seeds. The covered cultures are maintained in a

constant temperature room (70°F.)to eliminate temperature as a variable and to prevent moisture distillation in the germinators which occurs

under fluctuating temperahres. Several salinity levels were set up, ranging from 0.05 to 0.4 per cent sodium chloride on a dry soil basis. The

osmotic pressures of the soil solutions, calculated from the electrical

conductivity of the saturation extract and the soil moisture content at

time of planting, ranged from 0.7 to 25.3 atm.

Alfalfa, sugar beets, two varieties of barley, Mexican June corn and

red kidney beans were tested. No seeds germinated a t the 0.4 per cent

level, but barley, (California Marriout), gave 80 per cent germination a t

the 0.3 per cent salt level (20 atm. osmotic pressure). Although alfalfa

and sugar beets are regarded as salt tolerant crops, the data indicate

that they are relatively sensitive during germination. Alfalfa gave 80

per cent germination with 0.1 per cent added salt (7.3atm. osmotic pressure) and the germination of sugar beets was reduced to 50 per cent a t

5.8 atm. osmotic pressure. Corn, which is less tolerant than sugar beets

or alfalfa during later stages of growth, gave satisfactory germination

(93 per cent) a t approximately 10 atm. osmotic pressure and red kidney

beans, which are very sensitive to salt, germinated slightly better than

sugar beets. These data indicate that there is not always a positive

correlation between salt tolerance a t germination and during later phases

of growth.

The differential toxic effects of salts 01: ions in the substrate on germination and the development of the embryo and seedling have been studied

by a number of inxestigators. Harris (1915) found the relative toxicity

of soluble salts to be in the following descending order: NaC1, CaC12,

KCl, MgCL, KN03, Mg(NOd2, NazC03, NazSO, and MgSOr. With

respect to antagonism, he concluded that the effect of combined salts was

not so great in soils as in solution cultures. Harris and Pittman (1918)

in a continuation of the above study compared the relative toxicity of

NaCl a t concentrations of 0 to 4,000 p.p.m. and of NazCOs and NazSOl



PLANT GROWTH ON SALINE AND ALKALI SOILS



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at concentrations up to 10,000 p.p.m. a t moisture levels ranging from 20

to 32 per cent. Up to 1,000 p.p.m., all salts were beneficial, but above

1,500 p.p.m. all salts were increasingly toxic, chloride being most so, sulfate the least, and carbonate halfway between.

The alkali carbonates are usually found to be the most toxic salts.

Stewart (1898) found Na2S04 less injurious than NaCl and Na2C03

most toxic. Kearney and Harter (1907) tested seedlings of maize,

sorghum, oats, cotton and sugar beets in water cultures, using NaC1,

MgC12 and MgS04 as single salts, to determine the critical concentrations

a t which half of the root tips of seedlings exposed to these concentrations

for 24 hours failed to survive when subsequently transferred to water.

They found great differences in resistance to magnesium and sodium salts

in solution among the eight species tested, maize being most resistant and

cotton the least. The presence of CaS04 in excess greatly diminished the

toxicity of magnesium and sodium salts, the neutralizing effect being

greatest when added to MgS04 cultures and least in combination with

Na2C03. Rudolfs (1925) found that presoaking in distilled water retarded germination of all seeds, and noted differential responses to various single salts. All seeds were injured in K2C03 solutions and abnormalities occurred when this salt or MgS04 was used. C a ( N O d 2 had a

detrimental effect on germination and root, growth with nearly all varieties of seeds except corn.

Uhvits (1946) studied the effect of osmotic pressure on water absorption and germination of alfalfa seeds using concentrations of sodium

chloride and mannitol ranging from 1 to 15 atm. osmotic pressure. These

tests were made on filter paper in Petri dishes maintained at a constant

temperature of 71°F. 2". Other tests were made in sand cultures under

greenhouse conditions using sodium chloride a t concentrations of 1 to 12

atm. osmot,ic pressure. She found that germination was virtually inhibited when N a C l solutions of 12 to 15 atm. osmotic pressure were used,

and that reduction and retardation of germination were greater on N a C l

than on mannitol substrates. The difference in response on the tewo

substrates a t isomotic concentrations suggests a toxic effect of N a C l and

this assumption is supported 'by data showing the accumulation of

chloride in alfalfa seeds after 4 days of treatment. For example, on a

dry weight basis the per cent chloride in the seeds increased from 0.04

per cent in t a p water to 1.18 and 1.79 respectively on the 3 and 15 atm.

substrates. The data indicate that a t high concentrations, total absorpt.ion values were greater with mannitol than with sodium chloride; consequently if given enough time, relatively high germination rates were

obtained with mannitol a t 12 and 15 atm. (71 and 57 per cent, respectively). That high concentrations of sodium chloride are toxic is



*



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H. E. HAYWARD AND C. H. WADLBIGH



supported further by studies which showed that recovery of seeds transferred from a 12 atm. substrate of sodium chloride to tap water was considerably greater than the recovery of seeds treated for the same length

of time on a 15 atm. substrate of NaCl. The percentage of deformed

seeds on the sodium chloride substrate a t 15 atm. osmotic pressure was

greater than a t 12 atm., and the number of deformed seedlings in all concentrations of sodium chloride was much greater than in the corresponding concentrations of mannitol.

The influence of tcmperature as related to the effect of salt on germination should be mentioned. Ulivits (1946) found that. an increase in

the mean greenhouse temperature of 5°F. reduced the per cent germination a t all levels of salt treatment, the differences being more pronounced a t the higher salt levels. Ahi and Powers (1938) studied the

effect of temperature and other factors affecting salt tolerance using salt

grass, alfalfa, sweet clover, strawberry clover and Astmgulus rubyii as

test plants. The plants were grown in sand and water cultures; and sea

water, fortified with n nutrient solution and adjusted to salt concentrations ranging from 306 to 11,200 p.p.m., was used. I n one study wit.h

strawberry clover and alfalfa, temperatures were controlled a t 55", 70"

and 90°F. There was a definite decrease in the per cent germination with

increase of temperature or salt concentrat,ion. At 90°F. there was practically no germination regardless of salt level; but a t 55"F., 47.7 per

cent of the strawberry clover and 38 per cent of the alfalfa seeds germinated. The work of Ogasa (1939) on the effect of sodium chloride solut,ions on soybeans a t high and low temperatures confirms the above

findings. He found the limit of concentration of N a C l solutions a t which

germination occurred to be 200 m.e./l for high temperature (30°C.) and

300 m.e./l for low temperature (15°C.).

To summarize, it is evident that germination is retarded or inhibited

by the presence of soluble salts in the soil and that this effect is related

primarily to the osmotic pressure of the soil solution. As osmotic pressure increases, rate and per cent germination decrease. There is evidence

that certain salts or ions may be toxic to the embryo or seedling if occurring in sufficiently high concentrations. This toxicity may be reflected

in reduced germination and is frequently accompanied by abnormalities

in the growth and development of the seedling. High temperature is an

important consideration ; and, a t isosmotic concentrations of salt, per cent,

germination decreases with increase of temperature above optimum

levels. The studies reported indicate that species and varieties of plants

exhibit varying degrees of salt tolerance with respect to germination and

seedling growth, and they emphasize the importance of crop selection on

the basis of salt tolerance in areas where salinity is a problem.



PLANT GROWTH ON SALINE AND ALKALI SOILS



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2. Vegetative Growth and Maturation



Vegetative growth is retarded as the osmotic pressure of the substrate

is increased. Buffum (1896) noted that growth is in proportion t o the

amount of salts present in the substrate and similar conclusions were

reached by Harris (1915), Harris and Pitt.man (1918), Hayward and

Spurr (1944), and others. Eaton (1942) in studies on the toxicity of

chloride and sulfate salts has pointed out that the growth depression

curves showed no evidence of an abrupt point a t which the effect of

increasing osmotic pressure became pronounced. Magistad et al. (1943)

reported that growth reduction was in most cases linear with increasing

osmotic concentration of the substrate, and Gauch and Magistad (1943)

in a study of the effect of salt on legumes, found no evidence that there

is a given concentration of solution which may be regarded as critical,

but, rather there tended to be a linear relationship between growth reduction and increase in salt concentration of the solutions as expressed in

atmospheres.”

The first effect of increasing concentration of salt on vegetative development is usually a reduction in rate of growth which may not be

accompanied by any visible symptoms of injury. As Eaton (1942) has

pointed out, this absence of leaf symptoms of diagnostic significance or

other pronounced outward abnormalities suggests “that a substantial

proportion of the curtailed production of crops in irrigated areas that

was attributed to nutritional deficiencies or unfavorable water relations

was in fact due to saline conditions customarily regarded as insufficiently

high to be a cause of reduced yields.”

Under marginal conditions of salinity, and in t.he absence of detectable symptoms of salt injury, it is difficult to recognize salt effects

under field conditions. Controlled studies, however, have shown that

there may be morphological changes before other symptoms are evident.

I n general, the first physiological reaction to increased salt concentration is reduced entry of water into the roots (Hayward and Spurr, 1944;

Long, 1943; Rosene, 1941; and Tagawa, 1934). This tends to inhibit

meristemat,ic activity and elongation of the root (Hayward and Spurr,

1943). Hayward and Long (1941) have shown that the growth of tomato

stems as measured by height, diameter and dry weight was less a t high

salt concentrations than at control levels. The smaller diameter of stems

was correlated with significant differential reductions in the tissue systems. I n general, the reduction in thc vascular system on the basis of

percentage of total area was greater than that of the parenchymatous

tissues of the cortex and pith. Cambial act.ivity was inhibited and secondary xylem vessels and fibers were smaller in diameter and propor-



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H. E. HAYWARD AND C. H. WADLEIGH



tionately thicker walled. Somewhat similar results were observed for

flax (Hayward and Spurr, 1944) grown under high concentrations of salt.

The cambium was less active, the cells of the secondary xylem were

smaller, and the number and diameter of the phloem fibers was less than

in the control plants.

Various effects of increased salt concentrations on the growth and

structure of leaves have been reported, Harter (1908) working with

wheat, oats, and barley, found that increasing the salinity of a nonsaline

soil to 0.5 per cent soluble salts on a dry weight basis caused significant

modifications in leaf structure. The leaves developed a pronounced waxy

bloom, a thickened cuticle, and the size of the epidermal cells was decreased. Uphof (1941) in his review on halophytes, points out that such

plants show a tendency towards succulence by having thicker leaves and

stems, more pronounced palisade parenchyma and smaller intercellular

spaces. Lesage (1890) working with three nonhalophytes Pisum sativum,

Linum grandiflorum and Lepidium sativum, found that sodium chloride

produced thicker leaves, st.rengthened the palisade parenchyma, and reduced the intercellular spaces. Hayward and Long (1941), using osmotic

concentrations ranging from 0.5 to 6.0 atm., noted increases in the thickness of tomato leaves of from 9 to 30 per cent a t the 4.5 and 6.0 atm.

levels. The increased succulence of leaves was in agreement with results

reported by Wuhrmann (1935) who found that the thickness and degree

of succulence of leaves of Lepidium sativum and Nicotiana could be

modified by the addition of sodium chloride to nutrient solutions. Eaton

(1942), on the other hand, found no increase in the succulence of leaves

of milo, cotton, tomato, and sugar beets, or in alfalfa plants when the

osmotic pressure of the substrate was increased. I n barley, he found

succulence decreased with the additions of salt.

Recent studies by Bernstein and Ayers * have provided additional

information which indicates that with increasing levels of salinity succulence of leaf tissues may be either decreased or increased. Decrease in

succulence has been obtained with some cucurbits and with alfalfa and

grasses. With some crops, however, succulence increases with salinity.

Bean leaves have shown this response to salinity in both field plot and

water culture studies. I n other cases, there is little effect of salinity on

succulence. Tomato leaves in a field plot experiment showed increased

succulence a t low and medium salt levels, but a t high salt levels there

was no change in succulence as compared with leaves of the control plants

grown in nonsaline plots.

Tomatoes have been used in several studies to illustrate the effect of

salt on vegetative growth and yield. Eaton (1942) tested the growth and

yield of Stone tomatoes on substrates adjusted to .72 (control), 2.5 and



PLANT GROWTH ON SALINE AND ALKALI SOILS



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6.0 atm. with sodium chloride as the added salt. The relative dry weights

of t,he vines excluding fruit were 100, 77 and 27 per cent respectively and

those of the fruits were 100, 81, and 4 per cent. Hayward and Long

(1943) obtained comparable results with Marglobe tomatoes using NaCl

and NazSOl at osmotic pressures ranging from 1.6 to 7.7 atm. Their

work indicated that the osmotic pressure of t.he substrate was more

significant than the specific effect of the C1- and SO4= ions in relation

to vegetative responses and production of fruit. Other crops where tshis

generalization appears to hold are flax (Hayward and Spurr, 1944), beans

(Ayers et al., 1943) and peaches (Hayward et al., 1946).

Visible symptoms of salt injury may occur if the salt concentration

of t,he substrate is high. When chlorides are present, characteristic symptoms are incipient chlorosis accompanied by a drying and browning of

the apex of the leaf blade. The initial tip burn is usually followed by

progressive involvement of additional tissue extending along the margins

of the blade until one-half to two-thirds, or in some cases the entire

surface, becomes brown and necrotic. In severe cases, abscission of the

leaves occurs, dieback of the terminal axis or small branches is evident,

and death may ensue.

These symptoms have been described by Hayward et al. (1946) for

peaches, and Harper (1946) reports chloride injury for a number of trees

including pecan, elm, and ash, the tip burn and marginal browning being

most pronounced on the former. With one exception, scorched leaves

contained in excess of .88 per cent chloride in the ash content-. Hayward

and Blair (1942) observed moderate to severe chlorosis and tip burn on

leaves of Valencia orange seedlings on a substrate containing 50 m.e./l.

chloride and very severe symptoms when 100 m.e./l. of mixed chlorides

were added. Hayward, Cooil and Brown * studied the effects of NaC1,

CaCla and mixed chlorides on Marsh grapefruit grown in sand cultures,

with solutions adjusted to 0.5 (control), 2.5 and 3.5 atm. osmotic pressure. Incipient chlorosis and marginal and tip burn were evident after

two months, abscission of leaves was severe at 3.5 atm. osmotic pressure,

and at the end of 10 months the trees had lost approximately one-third

of their leaves. A t the highest level of salt concentration, vegetative

growth was reduced t o 45 per cent of the controls with mixed chlorides,

34 per cent with N a C l and to 22 per cent with CaCl2. Kelley and

Thomas (1920) studied the effects of excessive concentrations of salt in

irrigation water on citrus trees grown under orchard conditions. They

report that an excess of chlorides causes yellowing of the margins and tip

burn followed by heavy shedding of leaves on lemon trees. With orange

trees, mottle leaf was one of the first symptoms, sometimes accompanied

by browning and curling of leaves and dieback of young, tender shoots.



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H. E. HAYWARD AND C. H. WADLEIGH



Eaton (1942) observed somc yellowing in lemon leaves, with occasional

tip burn and subsequent abscission a t 50 m.e./l. chloride and noted

marked bronzing of leaves in an orchard where high chloride water was

used for irrigateion.

Barley, milo and navy bean leaves wcre burncd by chloride and sulfate

salts, but no injury was observed on alfalfa, cotton, tomato, and beet

plants (Eaton, 1942). Gauch and Wadleigh (1944) report darker green

color in the younger trifoliate leaves of bean plants tested on N a C l and

Na2S04 substrates and a pronounced marginal and tip burn a t high salt

concentrations (3.5 atm.) . Retzer and Mogen (1946) found that guayule

usually was killed when salt concentrations were 0.6 per cent in either

the first or second foot of soil and observed considerable amount of tip

burn in some fields, especially a t Coalinga, California.

Tip burn is not always associated with accumulations of the chloride

ion. Lilleland et al. (1945) have shown that sodium may cause tip burn

in almond trees and they describe symptoms which are very similar to

those noted above for chloride injury. They found moderate tip burn

where sodium in the leaf (moisture-free basis) ranged from 1.30 to 2.10

per cent. The scorch became worse as the season advanced and was

correlated with increasing accumulation of sodium.

Although high osmotic pressure of the substrate or soil solution usually results in depression of both vegetative growth and yield, exceptions

have been noted. Eaton (1942) found that the vegetative growth of

cotton plants was reduced relatively more by increased concentrations

of chloride and sulfate salts than was yield of seed cotton, but the differences were not great with chloride salts. Recent studies by Fireman and

Wadleigh * indicate that there may be differences in the vegetative and

fruiting responses of cotton t o increased levels of salinity. These differences may be related to variations in water regime, t o climatic factors,

or to the variety of cotton. Acala cotton was grown in salinized plots

adjusted to 0.1 and 0.2 per cent salt on a dry weight basis. The “dry”

plots received 20 surface inches of water in five irrigations, while thc

“wet” plots received 32 inches in sixteen irrigations. Vegetative growth

was better under the “wet” regime than on the “dry” plots a t all salt

levels, but in both series vegetative growth was reduced with increase

in salt concentration. Yield of seed cot,ton was inversely related to the

salt added in all cases except the “wet plot” with 0.1 per cent added salt.

I n a second study with Acala cotton this exception did not occur. Ayers

and Wadleigh * tested eight varieties of western barley in salinized plots

irrigated with water to which 3,000, 6,000, and 9,000 p.p.m. of salt were

added. The salts were supplied as a 50-50 mixture of sodium and

calcium chlorides. On the average, the levels of salinization had no effect



PLANT GROWTH ON SALINE AND ALKALI SOILS



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on the yield of grain, but thc lowest yields of straw and the highest

grain-draw ratios were found in the highest, salt t,reatment. The ratio

of grain to straw for eight varieties tested was .50 in the control.plots

and .72 under the 9,000 p.p.m. salt treatment.



VII. SPECIFICITY

IN SALTTOLERANCE

Early investigations indicated that various species and varieties of

crop plants exhibit differential salt tolerances when tested under uniform

conditions of salinity. Before the turn of the century, Buffum (1896)

pointed out that “the amount of alkali in the soil that is injurious to

crops depends upon its composition, the character of the soil, whether

the salts are upon the surface and the kind of crop grown,” Loughridge

(1901) .investigated the salt tolerance of fruit trees, truck, cereal and

forage crops grown under field conditions and reported his findings in

terms of the highest amounts of alkali in which the plants were unaffected

The relative tolerance was expressed as total alkali in lbs. per acre in 4

feet depth. H e also presented values showing the maximum tolerance for

each of the three salts commonly found, Na2S04, Na2COs and NaCI.

Hilgard (1906) in commenting on this work, points out that “it is certain

that the tolerance-figures will be quite different in presence of other salts,

from those that would be obtained for each salt separately; or for the

calculated mean of such separate determinations, proportionately prorated.” Harris (1920) recognized the difficulty of evaluating the relative

salt tolerance on the single basis of the quantity of salt that various crops

have been found to endure safely and pointed out that “soil, moisture,

climate, and perhaps other things will often change the relative tolerance

of the different crops to some extent so that slight differences in tolerance

mean little or nothing.”

Kearney and Scofield (1936) have reported on the choice of crops for

saline land using as a basis the percentage of soluble salts by weight to

the tot.al dry weight of the depth of soil reached by the roots. They set

up the following classes with respect t o degree of salinity: excessive, more

than 1.5 per cent; very strong, 1.0 to 1.5; strong, 0.8 to 1.0; medium

strong, 0.6 to 0.8; medium 0.4 to 0.6; weak, 0.1 to 0.4; and negligible, less

than 0.1. They recognized that a classification on a dry soil basis ignores

the soil-moisture relation by pointing out that “it is the concentration

of the soil solution and not the total quantity of salts present in the soil

which determines the effect on plant growth,” and assumed that “the soil

contains a degree of moisture favorable for the growth of the crop in

question.” Their studies dealt with the relative salt tolerance of crops

under the following classes: forage plants, root crops, cereals, fiber plants,

garden vegetables and truck crops, and trees and shrubs including fruit



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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-



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VI. Salt Tolerance as Related to the Life Cycle of the Plant

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