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V. How Saline and Alkali Soils Affect Plant Growth
PLANT GROWTH ON SALINE AND ALKALI SOILS
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
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).
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
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
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
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
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
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
H. E. HAYYWARD AND C. H.
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
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
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
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
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
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
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.
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.
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
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,
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