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VII. Specificity in Salt Tolerance
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
Forage plants, grasses and legumes, as a rule exhibit the highest
degree of salt tolerance on saline lands (Harris, 1920; Kearney and Scofield, 1936; Magistad and Christiansen, 1944), but there are marked
specific differences in this regard. The grasses are more salt resistant
than the legumes, outstanding species being alkali sacaton (Sporobolus
uiroides) , salt grass (Distichlissp&xzta),Nut,tall alkali grass (Puccinellia
Nuttalliana) ,Bermuda grass (CynodonDactylon),Rhodes grass (Chloris
gayuna), and western wheatgrass (Agropyron Smithii) . A number of
other grasses have been reported as having a moderate to high degree of
salt tolerance depending upon other factors. Studies a t Riverside, California, have indicated that the salt tolerance of some grasses is seriously
affected by high soil temperatures, i.e., reed canary grass, perennial ryegrass, meadow fescue and orchard grass (Wadleigh and Gauch *).
Among the leguminous forage plants, alfalfa, white and yellow sweet
clovers, birdsfoot trefoil, strawberry clover, and hubam clover are moderately salt tolerant (Harris, 1920; Kearney and Scofield, 1936; U. s.
Regional Salinity Laboratory, 1947). Ayers (1948) has found that birdsfoot trefoil (Lotus cmiculatus var. TENNUIFOLIUS) has a high salt tolerance and can withstand high summer temperatures. I n salinized plots
irrigated with water containing 5,000 p.p.m. added salts, the relative
yields, expressed as per cent of the yield on the nonsaline control plots,
were: birdsfoot trefoil, 43.6; California Common alfalfa, 40.4; and buf-
PLANT GROWTH ON SALINE AND ALKALI SOILS
falo alfalfa, 32.0. Birdsfoot trefoil gave better yields a t medium and
high salt levels (5,000 and 7,500 p.p.m .added salts) than big trefoil,
alsike, red, ladino, and strawberry clovers, in that order.
The data regarding the salt tolerance of strawberry clover appear to
be conflicting. Kearney and Scofield (1936) regarded it as outstanding
and reported satisfactory growth where the salt content of the surface
soil was more than 2 per cent, and Ahi and Powers (1938) rated it as
the most promising resistant legume followed by sweet clover and alfalfa.
On the other hand, Gauch and Magistad (1943) reported that on an
actual yield basis, alfalfa and ladino clover produced 1.3 and 1.9 times
as much forage, respectively, as strawberry clover, and Ayers (1948)
found that it failed to make an appreciable growth a t a high level of
salinity (irrigated with water containing 7,500 p.p.m. added salt). It
seems probable that climatic and soil moisture may account for t.he differences noted above. Strawberry clover appears to be well adapted to
wet, saline pastures and can tolerate high water tables and the cooler
Summer temperatures in the Northwest. The study of varieties of strawberry clover by Gauch and Magistad (1943) illustrates the possibility
of differences in salt tolerance within a species. Five strains were tested
at osmotic pressure of 0.5, 2.5, 3.5, and 4.5 atm. On the basis of actual
yields, significant differences in salt tolerance were observed with respect
to the strains from various sections of western United States.
The salt tolerance of alfalfa, one of the leading forage crops in the
Western States, has been studied extensively (Ahi and Powers, 1938;
Eaton, 1942; Gauch et al., 1943; Harris, 1920; Kearney, 1911;
Kearney and Cameron, 1902; Kearney and Scofield, 1936; and
Magistad e t al., 1943). It has been noted that alfalfa exhibits
differences in salt tolerance during its life cycle being more tolerant
with age (Harris, 1920; Kearney and Scofield, 1936), but there are
few data on the relative tolerance of varieties. Cooil and Brown *
a t the U. S. Salinity Laboratory have tested several varieties using
sand culture and soil plot technics. Six varieties, California Common.
Arizona Chilean, Ranger, Hegazi, Demnat and Tunisia, were tested
in large sand cult.ure tanks at salt concentrations from 0.5 to 6.5 atmowpheres. Based on relative yields, it was evident that there were significant varietal differences in salt tolerance. At the highest salt concentration (6.5 atm.), California Common yielded 77 per cent of t.he control
and Arizona Chilean 72 per cent, whereas Ranger produced only 38 and
Demnat 36 per cent. On an absolute yield basis, California Common,
Hegazi and Arizona Chilean were superior to other varieties tested.
Tests with California Common and Hegazi in salinized soil plots gave
11. E. HAYWARD AND C. H. WADLEIGH
consistently higher yields for the latter although relative yields on the
saliniaed plots were higher for California Common.
The cereals are moderately tolerant to salt, and some reports indicate
that they are more tolerant as forage than as grain crops, since the grain
may be inferior when grown under conditions of high salinity (Kearney
and Scofield, 1936; Magistad and Christiansen, 1944). Although reports
differ in regard to the relative tolerance of cereals; barley, rye, wheat and
oats for hay, and barley, rye, oats, rice, wheat and corn for grain have
been listed in that order of tolerance (U. S. Regional Salinity Laboratory, 1947).
There are few data on the salt tolerance of variet,ies of cereals.
Harris and Pittman (1919) tested the salt tolerance of a number of
varieties of oats, wheat, barley and corn, but their experiments were
primarily to determine relative germination and were terminated a t the
end of a 3-weeks growing period. Loughridge (1901) compared Russian
wheats and gluten wheat in field plots a t Tulare, California, and found
that the latter made good growth in soil containing 0.15 per cent salt..
Hayward and Uhvits * found White Federation 38 wheat, to be moderately salt tolerant and fair yields were obtained in sand culture studies
on a saline substrate containing 4 atm. (5,612 p.p.m.) of sodium chloride.
At this concentration, however, t.liere was a reduction of approximately
25 per cent in growth and yield of grain and there was some evidence
that the grain did not fill well when grown on the saline substrates.
Wasatch wheat was used by Reeve e t al. (1948) in leaching studies at
Delta, Utah. They found that yields varied inversely with the residual
salinity of the soil, and that a t low salt levels slight reductions in salt,
content resulted in large increases in yield. For example, a t one site,
(A), reduction in the conductivity of the saturation extract from 40 to
6 millimhos per cm. resulted in an increase in yield from 0.7 to 42.6
bushels per acre.
Recent studies by Ayers and Wadleigh * with eight varieties of barley
indicate a high degree of salt tolerance, and relative yields were not
reduced when the plots were irrigated with water containing 9,000 p.p.m.
added salt. The average conductivity of the saturated soil extracts for
the 0-16 inch depth a t this salinity level was 8.4 millimhos per cm. as
compared with 2.9 millimhos per cm. in the control plots. Corn is t,he
most salt-sensitive cereal and may not produce a satisfactory crop even
on slightly saline soils (Harris, 1920; Kearney and Scofield, 1936). Wadleigh et al. (1947) found Mexican June corn to be less salt tolerant than
alfalfa and more so than beans. Only a few roots penetrated a soil layer
containing 0.2 per cent salt and none were found in the layer where 0.25
per cent salt was added.
PLANT GROWTH ON SALINE AND ALKALI SOILS
Root and vegetable crops have a wide variation in salt tolerance
(Harris, 1920; U. S. Regional Salinity Laboratory, 1947). Sugar beets,
table beets, tomato, and asparagus, have shown good to moderate salt
tolerance, but most vegetable crops tested do not appear to be able to
withstand conditions of high salinity (Magistad and Christiansen, 1944).
Beans are very sensitive to salt; and carrots ,onions, lettuce and many
cucurbits have poor to moderate tolerance. Bernstein and Ayers * have
found that lettuce is least affected by given levels of salinity, cantaloupes
are intermediate and beans the most sensitive of these 3 crops. I n each
instance, several varieties were tested and varietal differences were noted
in some groups. With lettuce the relative salt tolerance of 6 variet
was not significantly different with the possible exception of Big Boston
which did not do well. Significant differences were found among varieties
of green beans and Giant Stringless Green Pod, Ranger, and Tendergreen
gave superior yields. Among curcurbits, the Cassaba melon gave higher
relative yields than for cantaloupe, and the cucumber and Conomon
melon were the least salt tolerant.
Sugar beets have good salt tolerance if a stand can be obtained
(Harris, 1920; Kearney and Scofield, 1936; Magistad and Christ.iansen,
1944). The relative sensitivity of this crop in thc germination and seedling stages has been reported in an earlier section. It was pointed out by
Shaw (1905) that (‘ the development of a more alkali-resistant beet
would make i t possible to extend considerably thc area now available
for beet crops.” He found that some beets could withstand salt concentration a t a depth of 2 feet up to 0.43 per cent on a dry soil basis.
Kearney and Scofield (1936) state that rz good stand of beets cannot be
expected if the soil contains more than 0.5 per cent salt. Harris (1920)
eets a lower value if quality is a consideration because increase in salt
concentration decreases yield of sugar. He states that sodium chloride
in excess of 0.04 to 0.05 per cent salt may reduce quality even though
beets will tolerate up to 0.4 per cent. Eaton (1942) using U. S. No. 1
sugar beets reports a high degree of tolerance to chloride, but not to sulfate salts, R greater reduction in yield resulting from 50 m.e./l. of sulfate
than from 150 m.e./l. of chloride addcd to a nutrient solution.
Among the fiber crops, cotton is very salt tolerant (Kearney and
Scofield, 1936; U. S. Regional Salinity Laboratory, 1947), and the long
staple or Egyptian types are more tolerant than the upland types.
Kearney (1911) states that cotton will tolerate 0.4 to 0.6 per cent salt
without injury. Cotton roots can readily penetrate soil containing 0.25
per cent sodium chloride wherc the critical osmotic pressure ranged from
16 t o 17 atm. (Wadleigh et al. 1947). Wadleigh and Gauch * have
studied many varieties of cotton in recent years, using a sand culture
H. 1. HAYWARD AND C. H. WADLEIGH
technic and single salts (NaC1, Na2S04 and CaCI2) adjusted to 4.5 atm.
osmotic pressure. All varieties were also grown in well-irrigated and
well-fertilized soil. A summary of yields for 12 varieties over a 3-year
period indicates a marked variation in relative salt tolerance. AmericanEgyptian varieties (SXP, Amsak and Sakel) , Acala 1517 and Acala P-18
have consistently shown a good salt tolerance, Stoneville strains made
very good relative yields on saline cultures but always showed marked
symptoms of salt toxicity. Other strains, Coker 100-6, Deltapine 14 and
Delfos 9252 have not produced well under control conditions a t Riverside, California, and do not. exhibit any marked degree of salt tolerance.
Flax is moderately salt tolerant (Hayward and Spurr, 1944; Kearney,
1911). Kearney and Scofield (1936) report good crops where the salinity
does not exceed 0.4 per cent. Hayward and Spurr (1944) in tests of
Punjab flax in sand cultures under greenhouse conditions found it to be
moderately salt tolerant. The tests were made a t osmotic concentrations
of 1.5 to 4.5 atm. using NaCl, CaClz and Na2S04 as single salts added to
a nutrient substrate. At high concentrations of salt (3.5 and 4.5 atm.)
relative yields of seed were reduced 25 to 62 per cent and no mature seeds
were produced at the highest concentration of sodium sulfate.
Information on the specific salt tolerance of trees and shrubs is
meager. The date palm is perhaps one of the most salt tolerant of all
cultivated plants (Harris, 1920). Magistad and Reitemeier (1943) report
fair growth of dates in the Imperial Valley where the soil solution a t a
moisture content near the wilting percentage contained 15,000 p.p.m. of
salts or an osmotic concentration of 7 atm. Figs, grapes and olives are
moderately salt tolerant, while citrus fruits, apples and pears, and drupaceous fruits are generally regarded as low in salt tolerance (Magistad
and Christiansen, 1944; U. S. Regional Salinity Laboratory, 1947).
Thrifty growth of Persian varieties of grapes has been observed in soils
containing as much as 0.28 per cent salt (Loughridge, 1901). Allison
and Christiansen i t reported good growth of Thompson seedless grapes in
the Coachella Valley, California, when the conductivity of the saturation
extract was as high as 3.5 millimhos/cm. in the second foot of soil. Hayward et al. (1946) report that the Elberta peach is sensitive to moderate
concentrations of salt and state that over a period of years yields can be
expected to decline if t,he salt concentration exceeds two atmospheres.
The Love11 rootstock appeared to be more suitable to moderately saline
conditions than the Shalil. Lilleland et al. (1945) have noted differential
toxicity to sodium in almonds. The Texas variety appears to be more
susceptible than Nonpareil, Ne Plus Ultra and others. Species of citrus
are quite sensitive to salt, especially to sodium chloride (Kelley and
PLANT GROWTH ON SALINE AND ALKALI SOILS
Thomas, 1920; Loughridge, 1901). Lemons are the most sensitive and
oranges occupy a position between lemons and grapefruit.
As Eaton (1942) has pointed out, it is difficult and frequently misleading to evaluate the salt tolerance of a species on the basis of appearance. This is especially true of trees and shrubs. There is good evidence
that the effect of saline substrates may be cumulative and that over a
period of years even low concentrations of salt may result in a slow but
progressive decline of a tree crop (Hayward e t al., 1946)
I n summary, two considerations may be stressed with respect to
specificity in salt tolerance. First, it is evident that there are marked
differences in relative salt tolerance among various genera, species and
varieties of agricultural crops. This fact emphasizes the importance of
proper selection of crops for use on lands that are marginal because of
salinity. It suggests also the necessity of furtsher testing and srreening
for salt tolerance on a genetic basis. The second point is that the various
criteria used for appraising salt tolerance may be inadequate if soil
moisture status and other factors are not taken into account.
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New Fertilizers and Fertilizer Practices
RANDALL J JONES A N D HOWARD T . ROGERS
Tennessee Valley Authority. Division of Agricultural Relations.
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . .
I1. New and Improved Fertilizer Materials . . . . . . . . . . . . . .
1. Phosphate Fertilizers . . . . . . . . . . . . . . . . . . .
a . Concentrated Superphosphate (40-50 Per cent PnOd . . . . .
b . Defluorinated Phosphates . . . . . . . . . . . . . . .
c. Phosphate Rock-Magnesium Silicate Glass . . . . . . . . .
d . Metaphosphates . . . . . . . . . . . . . . . . . . .
(1) Calcium Metaphosphate . . . . . . . . . . . . .
(2) Potassium Metaphosphate . . . . . . . . . . . . .
2. Phosphorus-Nitrogen Fertilizers . . . . . . . . . . . . . . .
a . Ammonium Phosphates . . . . . . . . . . . . . . . .
b . Dicalcium Nitraphosphate Products . . . . . . . . . . .
c. Ammoniated Superphosphate . . . . . . . . . . . . . .
3 . Nitrogen Fertilizers . . . . . . . . . . . . . . . . . . .
a . Ammonium Nitrate . . . . . . . . . . . . . . . . . .
b . Urea-Form . . . . . . . . . . . . . . . . . . . . .
c. Anhydrous Ammonia . . . . . . . . . . . . . . . . .
4 . Potash Fertilizers . . . . . . . . . . . . . . . . . . . .
5 . Mixed Fertilizers . . . . . . . . . . . . . . . . . . . .
I11. Recent Developments in Fertilizer Use . . . . .
. . . . . . .
1 High Rates of Fertilizer for Corn . . . . . . . . . . . . .
2. Use of Anhydrous Ammonia as a Fertilizer . . . . . . . . . .
3. Methods of Application . . . . . . . . . . . . . . . . . .
a . Furrow-Bottom or “Plow-Sole” Placement of Fertilizers . . . .
b . Subsurface Placement of Fertilizers for Sod Crops . . . . . .
c. Application of Fertilizers in Irrigation Water . . . . . . . .
d . Direct Application of Liquid Fertilizers . . . . . . . . . .
e . Plant-Nutrient Sprays . . . . . . . . . . . . . . . . .
4 . Fertilizing For Winter Grazing in the Southeastern States . . . . .
5 . Miscellaneous Practices . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . .
I . INTRODUCTION
The estimated fertilizer bill of the American farmer in 1947 was
615 million dollars Fertilizer consumption that year reached a figure of
16.000.000 tons. which was more than double that applied to soils in the
RANDALL J . JONES A N D HOWARD T. ROGERS
United States in 1939. It is believed that the 1948 figures will be somewhat in excess of those for 1947. Although fertilizer production has increased phenomenally during recent years, the current demand for many
materials still exceeds the supply.
A few years ago the north central region, an area of highly fertile
soils, was not considered to be of great importance from the standpoint
of fertilizer use. Now this is the most rapidly expanding fertilizerconsuming area in the United States, as reported by Mehring (1948). I n
the north central states plant-nutrient consumption increased from
Fig, 1. Increase in
U.S.fertilizer consumption, 1935-1947,by regions,
393,398 tons as an annual average for the 1935-39 period to 779,986 tons
in 1947, or an increase of 303 per cent. Significant increases in fertilizer
use have also occurred in the western states and in the traditionally highfertilizer-consuming Southeast, as illustrated in Fig. 1. With this upward
trend in consumption there has also developed, especially in the Midwest,
a demand for high-analysis materials.
Considerable progress has been made by the chemical engineer and
fertilizer chemist during recent years in the development of new fertilizers
and improvement of processes for fertilizer production. Likewise, the
agronomist, with assistance from specialists in other fields, has found
new ways of using fertilizer which add to its efficiency in crop production
and value for soil improvement,. These recent advancements have a farreaching significance for agricultural development in this country.