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V. How Saline and Alkali Soils Affect Plant Growth

V. How Saline and Alkali Soils Affect Plant Growth

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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.



PLANT GROWTH ON SALINE AND ALKALI SOILS



13



This problem may be illustrated by reference to Fig. 1 showing the

moisture tension curve of a sample of Panoche loam together with the

effect of increasing degrees of salinization upon the total soil moisture

stress as conditioned by t.he moisture content of the soil (Wadleigh, 1946).

The level of salinity in this instance is measured by an arbitrarily

chosen “Q value” which specifies the osmotic pressure of the soil solution.

The “total soil moisture stress” is defined as the summation of the

osmotic pressure of t,he soil solution and the soil moisture tension expressed in atmospheres.

The most useful concept of soil moisture from the agronomic standpoint, is the “available range” as delimited by “field capacity” and “permanent wilting percentage” (Veihmeyer and Hendrickson, 1927). The

soil moisture tension a t field capacity is evident.ly somewhere in the

neighborhood of 1/10 to 1/3 atm. The moisture retained by a soil in

equilibrium with a displacing force of 15 atm. has been found to approximate the permanent wilting percentage for many soils (Richards and

Weaver, 1943). Thus, the curve on the left. in Fig. 1 shows the change

in moisture tension between the field capacity and the permanent wilting

percentage of this sample of Panoche loam.

The hyperbolic nature of this curve is a prime consideration in the

evaluation of plant responses to variations in soil moisture in terms of

the energy status of the moisture. At the higher levels of soil moisture

within the “available range,” there is little change in the energy Bf

retention over a considerable range in moist.ure content, whereas a t

moisture levels just above the wilting percentage, there is a marked

change in surface force action with little change in moisture content.

This hyperbolic relationship is common to most soils and part.ially explains the observation that for all practical purposes under field conditions in the nonsaline soil, the soil moisture between field capacity and

permanent wilting percentage is “equally available” to the plant (Conrad and Veihmeyer, 1929; Hendrickson and Veihmeyer, 1929, 1942; and

Veihmeyer, 1927). Certainly, moisture withheld from the plant b y a

force of 15 atm. is not. as readily available as that retained by a forcc

of only 1/3 atm.; but, the hyperbolic relationship found for most soils

indicates that most of the available water is absorbed from the soil

before the moisture tension reaches 2 or 3 atm.

The remaining curves in Fig. 1 show how increasing concentrations of

salt in the soil affect the relationship between soil moisture stress and

moisture content. That is, the soil moisture stress may approach or even

exceecl a value of 15 atm. a t tlie moisture content of field capacity.

Richards and Weaver (1944) indicated that growth of most plants ceases



14



H. E. HAYWARD AND C. H. WADLEIGH



when the moisture tension reaches about 15 atm., and Wadleigh and

Gauch (1948) found that leaf elongation of cotton stopped when the

total soil moisture stress in a saline soil reached about 15 atm.

There is evidence, however, that different species of plants vary considerably as to the level of soil moisture stsress a t which symptoms of

marked water deficit will be in evidence, Wadleigh et al. (1947) grew

bean, corn, alfalfa, and cotton plants in containers of soil, 1 foot square

and 36 inches deep, varying in added salt content from none in the

surface 6 inches to 0.25 per cent a t the bottom. Observations on these

soil columns when the plants of each species were showing marked

moisture stress revealed that as the salt content of the soil strata increased, the roots of the various species showed a corresponding decrease

in their ability to remove water. Comparable cultures of nonsaline soil

showed that roots of all species were normally capable of penetrating the

deepest layer in the culture and removing all available water. I n the

salinized cultures, water was removed from each layer to such n degree

that final osmotic pressures of all layers in the soil column were nearly

uniform. These critical osmotic pressures of the soil solution were found

to be 7 to 8 atm. for beans; 10.5 to 11.5 atm. for corn; 12 to 13 atm.

for alfalfa; and 16 to 17 atm. for cotton. Wadleigh and Fireman (1948)

found a comparable inverse relationship in the patterns of salt distribution and water removal in the root zone of furrow-irrigated cotton.

On the basis of the preceding st.atements, it is evident that plant

growth on saline soil, as conditioned by water relations, involves an integration of the following variables affecting moisture availability in the

root zone: (a) variation in salt distribution within the soil mass and its

consequent effect on the variation in the osmotic pressure of the soil

solution a t a given moisture content; (b) variation in osmotic pressure in

relation to change in moisture content; (c) variation in moisture tension

in relation to moisture content; (d) variation in moisture content within

the soil mass a t a given time; and (e) variation in total water content

of the soil in the root zone with time. A mathematical method (Wadleigh, 1946) has been developed to integrate these variables and permit.

the derivation of the average moisture stress affecting the plant over an

extended period of time. It has been found that vegetative growth of

beans (Wadleigh and Ayers, 1945) and guayule (Wadleigh et al., 1946)

is rather closely related to the average moisture stress if other factors

are not limiting t o growth. The daily rate a t which cotton leaves enlarge

has also been found to be correlated with the intensity of the soil moisture stress (Wadleigh and Gaucli, 1948).

I n summary, one of the main effects of moderate levels of soil salinity



PLANT GROWTH ON SALINE AND ALKALI SOILS



15



is that of limiting water supply to the plant and thereby inducing those

modifications in plant behavior normally associated with water deficits

in the tissues. Obviously, a soil may become sufficiently saline to prevent

even the growth of halophytes, just as it may become too dry to support

growth of xerophytes.

Depending on the species, each of the various components that may

be present in saline solutions may have some specific toxic effect on the

plant over and above that which may be accounted for on the basis of

the osmotic pressure of the soil solution.

The ions which may accumulate in saline soils are: N a + , C a + + ,

Mg++, K+, C1-, SOa=, HC03-, and NOs-.

a. Sodium. There is relatively little evidence that indicates positively

the specific toxicity of the sodium ion to plants growing in saline soils.

Many species tend to exclude sodium (Collander, 1941; Gauch and Wadleigh, 1945; Hayward e t al., 1946; Wallace et al., 1948); and specific

toxic effects may arise from such exclusion of sodium along with accumulation of accompanying anions from the substrate (Hayward, 1946).

Such instances should not be classed as sodium toxicity.

Lilleland e t al. (1945) found that a tip-burn condition on almond

leaves in California was directly related to the sodium content of the

leaf. Neither the salinity of the soil nor the sodium content of the soil

solution was high, and the condition may have been more indicative of

an alkali soil condition rather than salinity. It is possible that accumulation of sodium within the plant may be associated with a depression in

the accumulation of the other cations to the extent that their content

may be below adequate levels, or an unfavorable cationic balance may

be induced. Whether or not such a condition should be designated as

sodium toxicity is merely a question of definition. At present, there

exists little clearcut evidence that strictly saline soils may induce sodium

toxicity per se.

b. Calcium. The calcium ion may accumulate to high concentrations

in saline soil solutions, and this concentration may be specifically toxic.

The specific effect of high concentration of calcium varies with the

species. For example, guayule was found to be relatively more tolerant

of a saline substrate induced by CaClz than to those induced by other

neutral salts (Wadleigh and Gauch, 1944). Masaewa (1936) found that

applications of CaClz to soil cultures of flax were more highly toxic than

applications of NaC1. The chloride ion accumulated to high levels in

the plants on CaClz cultures, so she ascribed the difficulty to chloride

toxicity and to an unfavorable Ca/K ratio since Ca was also found to

accumulate to rather high levels. Wadleigh and Gauch * observed the

same effect on orchard grass, but they also' noted that salinization of the



16



H. E. HAYYWARD AND C. H.



WADLnIGH



soil with Ca(N03)a had the samc effect as CaC12. There was a high

accumulation of Ca in orchard grass on the Ca(N03)2 treatments but

only a small amount of chloride, hence chloride toxicity was not involved.

Ayers * has secured comparable data for tall fescue grass. Lehr (1942)

attributes the stimulative effect of sodium on sugar beets to the fact that

the sodium effectively counteracts absorption of calcium, thereby preventing the development of what hc calls a “calcium-type-plant.” Such

a plant has a bluish-green east and appears to be stunted in growth.

c. Magnesium. High accumulations of magnesium in the substrate

have been found to be especially toxic to plants over and above any

inhibition in growth that might be associated wit.h osmotic pressure (de

Sigmond, 1938; Trelease and Trelease, 1931 ; Wadleigh and Gauch, 1944).

Magnesium injury may be associated with an inadequate supply of calcium

within the tissue (Gauch, 1940). Both Ayers * and Wadleigh and Gauch *

have obtained evidence that plants may not show specific symptoms of

magnesium toxicity under conditions of accumulated magnesium in the

soil solution when calcium ions are also present, a t a relatively high level.

d. Potassium. Accumulations of potassium in the soil solut.ian are

rather rare, but they may occur. If such an accumulation is partially

balanced by calcium no specific inhibitive effects of potassium on plant

response are noticeable (Ayers *; Wadleigh and Gauch *) . Cases have

been reported in which relatively high levels of potassium have induced

characteristic symptoms of iron chlorosis (Walsh and Clarke, 1942) and

magnesium deficiency (Boynton and Burrell, 1944).

Cations differ markedly in their effect upon the physical properties

of the colloidal constituents of protoplasm; and there are pronounced

antagonistic effects exhibited between various cation pairs in counteracting the adverse effect of one or both cations upon protoplasmic activity

(Chambers et al., 1937; Heilbrunn and Daugherty, 1932; Moyer and Bull,

1935). As Lundegbrdh (1940) points out, the monovalent cations have

such a dispersive effect upon protoplasmic colloids that they may induce

complete disorganization and deat.h unless balanced by a divalent cation,

especially calcium. On the other hand, the divalent ions tend to have a

coagulative eff eet and may seriously inhibit permeability of the membranes. There are instances, however, in which the effect of Mg++ on

protoplasm is more nearly comparable to K+ and Na+ than to C a + +

(Heilbrunn and Daugherty, 1932). Hence the frequently noted mutual

antagonism between Ca++ and Mg++. It is apparent that, species differ

widely as to the extent to which they may be susceptible to the adverse

effect of abnormally wide ratios between various cations.

e. Chloride. There has been some tendency to regard chloride toxicity

and the adverse effect of soil salinity as synonymous. For many species of



PLANT GROWTH ON SALINE AND ALKALI SOILS



17



plants, chloride salts are no more inhibitive to growth than isosmotic concentrations of sulfate salts (Eaton, 1942; Hayward and Long, 1941; Magistad, et al. 1943). Eaton (1942) found that lemon cuttings, navy beans,

and dwarf milo were more sensitive to chloride than to isosmotic concentrations of sulfate when grown in sand cultures. Hayward et al. (1946)

noted that peach trees were especially sensitive t o chloride salts, and

Harper (1946) that pecans were quite sensitive to chloride. The work of

Garner et al. (1930) on tobacco provides a good insight into the mechanism of chloride toxicity. They found that the high level of chloride accumulation in tobacco leaves resulting from heavy fertilization with potassium chloride was associated with a pronounced dissipation of the malic

acid content of t.he leaves. Since the organic acids are the major components of the buffer mechanism of plant cells, conditions effecting dissipation of organic acids could have a significant effect on the pH control

within the cell and the associated activity of the protoplasm. These investigators also noted that if the tobacco plant receives an excess of

chloride the normal amylolytic activity is disturbed and the leaves become gorged with starch. Baslavskaja (1936) observed that accumulation

of the chloride ion in potato leaves interferes with the photosynthetic

mechanism, i.e., causes a reduction in chlorophyll content; and, consequently, a reduction in total carbohydrate content, even though there was

a definite increase in the starch/sugar ratio. Schuphan (1940) concluded

from his data that it is not possible to make sweeping conclusions as to

the effect of chloride on carbohydrate metabolism since species vary so

greatly in their response to the chloride ion.

Beneficial effects from added chloride salts have been noted for table

beets (Raleigh, 1948), sugar beets (Eaton, 1942; Tottingham, 1919)

tomato (Eaton, 1942), and spinach (Schuphan, 1940).

f. Sulfate. There are numerous observations on several species of

crop plants indicating specific toxicity of high concentrations of the

sulfate ion. This has been reported for flax (Hayward and Spurr, 1944),

tomato (Eaton, 1942), cotton and orchard grass (Wadleigh and Gauch"),

and leek (Schuphan, 1940). But there is a dearth of information to

explain why the sulfate ion has an inhibitive effect on the growth of

certain species. Harris et al. (1925) found that Egyptian cotton varieties

tend to accumulate considerably more chloride in their tissues than do

American upland varieties, and that the converse tendency was expressed

with respect to the sulfate ion. Cotton variety tests conducted in large

outdoor sand cultures by Wadleigh and Gauch * failed to show any clearcut distinction between these two types of cotton in their respective

tolerance of high accumulations of sulfate. It is obvious, however, that

high concentrations of sulfate in the substrate definitely limit the activity



18



H. E. HAYWARD AND C. H. WADLEIGH



of the calcium ion and thereby condition cationic intake by plants.

Analyses of leaves of beans (Gauch and Wadleigh, 1945), peach trees

(Hayward et al., 1946), orchard grass and cotton (Wadleigh and Gauch ")

showed that the tissues contained an appreciably lower content of calcium and higher contents of sodium and potassium when sulfate was the

predominant anion in the substrate as compared to similar cultural conditions in which chloride was the predominant anion. It may be presumed

that specific adverse effects of sulfate are related to a disturbance in

the optimum cationic balance within the plant, but the evidence is too

limited t o warrant a broad generalization.

g. Bicarbonate. As pointed out by Heller et al. (1940), the bicarbonate ion is quite toxic to plants. They noted that the presence of accumulations of bicarbonate in the substrate markedly inhibited the intake of

calcium by plants. Harley and Lindner (1945) reported that apple

orchards in Washington irrigated with water relatively high in bicarbona.te tended to become chlorotic, and that the condition could be partially

alleviated by subsequent irrigation with low bicarbonate water. They

found also a heavy incrustation of calcium and magnesium carbonates

upon the roots of the apple trees in orchards which had been irrigated

for some time with water relatively high in calcium and magnesium

bicarbonates. They suggested that such a condition could seriously affect

the mineral nutrition of the tree, and as a consequence induce the symptoms of chlorosis so frequently observed. Gauch" found evidence of

marked specificity in tolerance of the bicarbonate ion. His data showed

that the addition of 12 m.e./l. of bicarbonate to a nutrient solution had

virtually no effect on the growth of Rhodes grass, whereas the same concentration caused Dallis grass to become seriously chlorotic or to bc

killed. Increasing concentrations of bicarbonate have caused pronounced

chlorosis and inhibition of growth in beans (Wadleigh and Brown")

whereas the same treatments effected a comparably small decrease in

growth and little visual evidence of chlorosis on garden beets (Brown and

Wadleigh ")

Steward and Preston (1941) studied the effect of bicarbonate on ionic

absorption and metabolism by potato disks. At a constant pH, increasing the external concentration of potassium bicarbonate depressed botli

protein synthesis and bromide accumulation. Indirect evidence indicated

that KHC03 also depressed respiration and carbohydrate metabolism.

The study with bean plants (Wadleigh and Brown") showed tshat increasing concentrations of bicarbonate induced a pronounced depression

in the intake of calcium, and an increase in intake of potassium. I n

beets, with their normally low calcium content, intake of calcium was

not affected, that of magnesium was depressed markedly, that of potas-



.



PLANT GROWTH ON SALINE AND ALKALI SOILS



19



sium depressed slightly, and intake of sodium increased. These data

serve to illustrate that the adverse effect of bicarbonate upon plant

response is intimately associated with the specificity of the plant with

respect to ionic intake and metabolism.

h. Nitrate. The nitrate ion may accumulate to rather high levels in

certain naturally saline soils, the condition being characterized as the

development of “niter spots” (Stewart and Peterson, 1915). There are

several instances known in which high levels of nitrate supply inhibited

growth (Chapman and Liebig, 1940; Eaton and Rigler, 1945; Leonard

et al., 1948), but it is usually difficult to draw a olearcut distinction

between any specific effect of the nitrate ion and concomitant effects induced by the higher osmotic pressure of the substrate or the effect of the

complementary cations. Howcver, Headden’s early observation (1912)

that nitrate accumulations in the soil contribute to the production of

inferior quality sugar beets because of low sugar content has been verified

many times.

6. Alkali Soils

Kelley (1928) suggested 20 years ago that the presence of a relatively

high proportion of sodium on the exchange complex of soils may prevent

the plant roots from obtaining an adequate supply of calcium because

of “the pronounced avidity of the sodium-exchange complex for calcium.”

This effect of adsorbed sodium on the availability of calcium has been

observed many times (Gedroix, 1931; Ratner, 1935, 1944; Thorne, 1944;

Van Itallie, 1938). For most crop plants, the calcium becomes unavailable

when the exchangeable-sodium-percentage approaches 50. Bower and

Turk (1946) found that high percentages of exchangeable potassium were

just as effective as those of sodium in preventing calcium and magnesium

availability to plants.

Although alkali soils may actually have an acid reaction, many are

found that have a p H of 9 or even 10. Few if any crop plants can thrive

under such alkalinity. Arnon and Johnson (1942) grew tomatoes, lettuce

and Bermuda grass in nutrient solution in which a range from p H 3 to

pH 9 was maintained. Although all three species were tolerant of a

wide range in p H value of the subshate, a marked decline in growth

was observed a t pH 9. Breazeale and McGeorge (1932) found that the

carbon dioxide content of alkaline-calcareous soils was extremely low.

They concluded that the low level of COz in such soils was a major factor

in the lack of availability of phosphate which also was observed for these

soils. That is, their observations indicated that phosphorus unavailability was the major limiting factor in these alkaline-calcareous soils, and



20



13. E. HAYWARD AND C. H. WADLEIGH



that this condition was brought about by thc low level of CO, occurring

in a substrate high in alkalinity.

Sodium soils readily become dispersed and a dispersed soil is not

conducive to vigorous growth of plants. McGeorge and Breazeale (1938)

studied the effect of puddled soils on plant growth, and found that plants

growing under normal conditions will wilt after the soil is puddled, even

though an abundant supply of moisture may be present. The puddled

soil has a lowered capacity for gaseous interchange which may result, in

oxygen deficiency a t the absorbing surfaces of the roots, and most plants

are unable to take in adequate quantities of water a t low oxygen tensions.

These investigators also presented evidence that nutrient availability as

well as water availability is lowered in a puddled soil. Fireman and

Reeve (1948) made a study of alkali soils in Gem County, Idaho. I n

this area, barren islands of alkali soil are interspersed among soil areas

supporting fairly good crop growth. They made a study of various soil

attributes which might show a wide differential between soil supporting

good growth and adjacent barren areas. They found that rate of infiltration was the most consistent criterion, the poor infiltration on the

barren areas causing the soils to be deficient in moisture most of the time.

That is, the very poor structural status of the alkali soil in the barren

areas prevented a replenishment of the soil moisture reservoir that is

essential for plant growth.



VI. SALTTOLERANCE

AS RELATED

TO



THE



LIFE CYCLEOF



THE



PLANT



When the life cycle of the plant is considered in relation to salt

tolerance, it is desirable to recognize three phases of growth and development since the effect of salt may be different with respect to germination

and seedling growth, vegetative growth, and maturation and fruition.

1. Germination



Under saline soil conditions, the first phase, germination and seedling

growth, is critical, since the ability of a given variety to germinate and

est*ablishthe seedling is frequently the limiting factor in crop producton.

There are two ways in which saline soils may effect germination: (a)

there may be enough soluble salt in the seed bed to build up the osmot.ic

pressure of the soil solution to a point which will retard or prevent intake

of necessary water, and (b) certain constituent salts or ions may be toxic

to the embryo and seedling.

The effect of high osmotic pressure of the soil solution was investigated in early work by Buffum (1896, 1899) who concluded that “the

retarding effect of a salt solution on the germination of seeds is in direct

proportion to its osmotic pressure when the solutions are strong.’’ Similar



PLANT GROWTH ON SALINE AND ALKALI SOILS



21



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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