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Introduction
The agricultural use of saline water or soils can benefit many
developing countries. Salt-tolerant plants can utilize land and water
unsuitable for salt-sensitive crops (glycophytes) for the economic pro-
duction of food, fodder, fuel, and other products. Halophytes (plants
that grow in soils or waters containing significant amounts of inor-
ganic salts) can harness saline resources that are generally neglected
and are usually considered impediments rather than opportunities
for development.
Salts occur naturally in all soils. Rain dissolves these salts, which
are then swept through streams and rivers to the sea. Where rainfall
is sparse or there is no quick route to the sea, some of this water
evaporates and the dissolved salts become more concentrated. In
arid areas, this can result In the formation of salt lakes or in brackish
groundwater, salinized soil, or salt deposits.
There are three possible domains for the use of salt-tolerant
plants in developing countries. These are:
1. Farmlands salinized by poor irrigation practices;
2. Arid areas that overlie reservoirs of brackish water; and
3. Coastal deserts.
In some developing regions, there are millions of hectares of
saTinized farmland resulting from poor irrigation practices. These
lands would require large (and generally unavailable) amounts of
1
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2
water to leach away the salts before conventional crops could be
grown. However, there may be useful salt-tolerant plants that can be
grown on them without this intervention. Although the introduction
of salt-tolerant plants will not necessarily restore the soil to the point
that conventional crops can be grown, soil character is often improved
and erosion reduced.
Moreover, many arid areas overlie saline aquifers groundwater
containing salt levels too high for the irrigation of conventional, salt-
sensitive crops. Many of these barren lands can become productive
by growing selected salt-tolerant crops and employing special cultural
techniques using this store of brackish water for irrigation.
Throughout the developing world, there are extensive coastal
deserts where seawater is the only water available. Although growing
crops in sand and salty water is not a benign prospect for most farm-
ers, for saline agriculture they can complement each other. The dis-
advantages of sand for conventional crops become advantages when
saline water and salt-tolerant plants are used.
Sand is inherently low in the nutrients required for plant growth,
has a high rate of water infiltration, and has low water-holding
capacity. Therefore, agriculture on sand requires both irrigation
and fertilizer. Surprisingly, 11 of the 13 mineral nutrients needed
by plants are present in seawater in adequate concentrations for
growing crops. In addition, the rapid infiltration of water through
sand reduces salt buildup in the root zone when seawater is used for
irrigation. The high aeration quality of sand is also valuable. This
characteristic allows oxygen to reach the plant roots and facilitates
growth. Although careful application of seawater and supplementary
nutrients are necessary, the combination of sand, saltwater, sun,
and salt-tolerant plants presents a valuable opportunity for many
developing countries.
Of these three possibilities for the introduction of salt-tolerant
plants (sal~nized farmland, undeveloped barren land, and coastal
deserts), the reclamation of degraded farmland has several advan-
tages: people, equipment, buildings, roads, and services are usually
present and a social structure and market system already exist. The
potential use of saline aquifers beneath barren lands depends on
both the concentration and nature of the salts. The direct use of
seawater for agriculture is probably the most challenging potential
application.
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3
Most contemporary crops have been developed through the do-
mestication of plants from nonsaTine environments. This is unfortu-
nate since most of of the earth's water resources are too salty to grout
them. From experience in irrigated agriculture, Miyamoto (personal
communication) suggests the following classification of potential crop
damage from increasing salt levels:
Irrigation Water Salts, ppm
Crop Problems
Fresh <125 None
Slightly saline 125-250 Rare
Moderately saline 25~500 Occasional
Saline 50~2,500 Conunon
Highly saline 2,500-5,000 Severe
Colorado River water, used for irrigation in the western United
States, contains about 850 ppm of salts; seawater typically contains
32,00~36,000 ppm of salts. Salinity levels are usually expressed in
terms of the electrical conductivity (EC) of the irrigation water or
an aqueous extract of the soil; the higher the salt level, the greater
the conductivity. The salinity of some typical water sources is shown
in Table 1.
TABLE 1 Water Salinity.
. .
megaton
Salinity Water Quality Colorado Alamo Negev Pacific
Measurement (Good) (Marginal) River River Groundwater Ocean
Electrical
conductivity
(dS/m)* 0-1 1-3 1.3
4.0 4.0 - 7.0 46
Dissolved
solids, ppm 0-500 500-1,500 850 3,000 3,000-4,500 35,000
*1 dS/m = 1 mmho/cm = (approx.) 0.06%NaC1 = (approve.) 0.01 mole/1 NaCl.
10,000 ppm = 10 o/oo (parts per thousand) = 10 grams per liter = 1.0%
In the International System of Units (SI), the unit of conductivity is the Siemens
symbol, S. per meter. The equivalent unit commonly appearing in the literature is
the mho (reciprocal ohm); 1 mho equals 1 Siemen.
SOURCE: Adapted from Epstein, 1983; Pastemak and De Malach, 1987; and Rhoades
et al., 1988.
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4
There are three broad approaches to utilizing saline water, de-
pending on the salt levels present. These include the use of marginal
to poor irrigation water with electrical conductivities (ECs) up to
about 4 dS/m, the use of saline groundwaters such as those in Israel's
Negev Desert with ECs up to about 8 dS/m, and the use of even
more saline waters with salt concentrations up to that of seawater.
At low, but potentially damaging, salt levels, Rhoades and
coworkers (1988) have grown commercial crops without the yield
losses that would normally be anticipated. Through knowledge of
crop sensitivity to salt at various growth stages, they used combina-
tions of Colorado River water and Alamo River water to minimize
the use of the higher quality water. For example, wheat seedlings
were established with Colorado River water; Alamo River water was
then used for irrigation through harvest with no loss in yield.
At higher salt levels, Pasternak and coworkers (1985) have devel-
oped approaches that involve special breeding and selection of crops
and meticulous water control. The agriculture of Negev settlements
in Israel is based on the production of cotton with higher yields,
quality tomatoes for the canning industry, and quality melons for
export all grown with EC 4-7 dS/m groundwater. Experimental
yields of a wide variety of traditional crops grown in Israel with
water with ECs up to 15 dS/m, are shown in Table 6 (p. 35~. In
west Texas (USA), Miya~noto and coworkers (1984) report commer-
cial production of alfalfa, melons, and tomatoes with EC 3-5 dS/m
irrigation water, and cotton with 8 dS/m irrigation water.
The use of water with still higher salt levels up to, including, and
even exceeding that of seawater for irrigation of various food, fuel,
and fodder crops has been reported by many researchers including
Aronson (1985; 1989), Boyko (1966), Epstein (1983; 1985), Gallagher
(1985), Glenn and O'Leary (1985), Tyengar (1982), Pasternak (1987),
Somers (1975), Yensen (1988), and others. These scientists have
produced grains and oilseeds; grass, tree, and shrub fodder; tree and
shrub fue~wood; and a variety of fiber, pharmaceutical, and other
products using highly saline water.
Thus, depending on the soil or water salinity levels, salt-tolerant
plants can be identified that will perform well in many environments
in developing countries. The salt tolerance of some of these plants
enables them to produce yields under saline conditions that are
comparable to those obtained from salt-sensitive crops grown under
nonsaline conditions.
The maximum amount and kind of salt that can be tolerated
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s
120
Oh 100
IL
cL ~ 80
O a,
> Q 60
40
20
\
Halophytes
Salt-Sensitive Crops
-
\ Salt-Tolerant Crops ~
0 5 10 15 20 25 30 35
SALINITY, dS/m
FIGURE 1 Growth response to salinity. Many halophytes, such as Suacda
maritime, have increased yields at low salinity levels. Salt-tolerant crops, such
as barley, maintain yields at low salinity levels but decrease as salt levels exceed
a certain limit. Yields of salt-sensitive crops, such as beans, decrease sharply
even in the presence of low levels of salt. SOURCE: Adapted from Greenway
and Munns, 1980; Maas 1986; and Yensen, et al., 1985.
by halophytes and other salt-tolerant plants varies among species
and even varieties of species. Many halophytes have a special and
distinguishing feature-their growth is improved by low levels of salt.
Other salt-tolerant plants grow well at low salt levels but beyond a
certain level growth is reduced. With salt-sensitive plants, each
increment of salt decreases their yield (Figure 1~.
Such data provide only relative guidelines for predicting yields
of crops grown under saline conditions. Absolute yields are subject
to numerous agricultural and environmental effects. Interactions
between salinity and various soil, water, and climatic conditions all
affect the plant's ability to tolerate salt. Some halophytes require
fresh water for germination and early growth but can tolerate higher
salt levels during later vegetative and reproductive stages. Some can
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6
germinate at high salinities but require lower salinity for maximal
growth.
Traditional farming efforts usually focus on modifying the en-
vironment to suit the crop. In saline agriculture, an alternative is
to allow the environment to select the crops, to match salt-tolerant
plants with desirable characteristics to the available saline resources.
In many developing countries extensive areas of degraded and
arid land are publicly owned and readily accessible for government-
sponsored projects. These lands are often located in areas of high
nutritional and economic need as well. If saline water is available,
the introduction of salt-tolerant plants in these regions can unprove
food or fuel supplies, increase employment, help stem desertification,
and contribute to soil reclamation.
LIMITATIONS
Undomesticated salt-tolerant plants usually have poor agro-
nom~c qualities such as wide variations in germination and matura-
tion. Salt-tolerant grasses and grains are subject to seed shattering
and lodging. The foliage of sal~tolerant plants may not be suitable
for fodder because of its high salt content. Nutritional characteristics
or even potential toxicities have not been established for many edible
salt-tolerant plants. When saline irrigation water is used for crop
production, careful control is necessary to avoid salt buildup in the
soil and to prevent possible contamination of freshwater aquifers.
Most importantly, salt-tolerant plants should not be cultivated
as a substitute for good agricultural practice nor should they be used
as a palliative for improper irrigation. They should be introduced
only when and where conventional crops cannot be grown. Also,
currently productive coastal areas (such as mangrove forests) should
be managed and restored, not converted to other uses.
All of these limitations are impediments to the use of conven-
tional methods for culture and harvest of salt-tolerant plants and the
est~rnation of their production economics.
RESEARCH NEEDS
-
Increased research on the development of salt-tolerant cultivars
of crop species could, with appropriate management, result in the
broader use of saline soils. In the early selection and breeding pro-
gra~ns of crop species for use in nonsaline environments, performance
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7
was improved through the considerable genetic variability present in
the unimproved crops and in their wild relatives. Since few crops
have been subjected to selection for salinity tolerance, it is possible
that variation In this characteristic may also exist. Conversely, few
undomesticated salt-tolerant plants have been examined for variabil-
ity in their agronorruc qualities, and it Is even more likely that such
characteristics can be improved through breeding programs.
In addition, germplasm collection and classification, breeding
and selection, and development of cultural, harvest, and postharvest
techniques are all needed. Basic information on the way in which
plants adapt to salinity would significantly assist their economic
development.
Exploration for new species should continue to identify candi-
dates for economic development. Research can then begin on ways
to improve the agronomic qualities of these plants and to utilize their
genetic traits. For example, seed from a wild tomato found on the
seashore of the Galapagos Islands produced tomatoes that were small
and bitter. When this species was crossed with a commercial tomato
cultivar, flavorful} fruit the size and color of cherry tomatoes were
obtained in 70 percent seawater.
Recent advances in plant biotechnology include work on salinity
tolerance and productivity. New techniques for in vitro selection of
genotypes tolerant to high salinity leveLs have been found to improve
the adaptability of conventional crops as well as assist in the selection
of desired genotypes from a wide range of natural variability in
individual salt-tolerant plants. Genotypes with increased tolerance
to water and salinity stress have been identified and followed in
genetic crosses with conventional genotypes using new techniques in
gene mapping and cell physiology.
Stress genes are now the target of research in genetic engineering.
The transfer of these genes from sources in salt-tolerant species to
more productive crops will require modifications in cultural practices
as well as treatment of the plant products.
Interdisciplinary communication is particularly important in re-
search on salt- tolerant plants. Cooperation among plant ecologists,
plant physiologists, plant breeders, soil scientists, and agricultural
engineers could accelerate development of economic crops. Further,
universities could introduce special programs to allow broad study
of the special characteristics of saline agriculture to serve growing
needs in this field.
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8
REFERENCES AND SELECTED ~AD~GS
Abrol, I. P., J. S. P. Yadav and F. I. Massoud. 1988. Salt-affceted Soils and Their
Management. Soils Bulletin 39, FAO, Rome, Italy.
Ahmad, R. 1987. Saline Agriculturc at Coastal Sandy Belt. University of Karachi,
Karachi, Pakistan.
Ahm ad, R. and A. San Pietro (eds.~. 1986. Prospects for Biosalinc Rcacarch
University of Karachi, Karachi, Pakistan.
Aronson, J. A. 1989. Haloph Salt tolerant Plants of the World University of
Arizona, Tucson, Arizona, US.
Aronson, J. A. 1985. Economic halophytes a global view. Pp. 177-188 in: G.
E. Wickens, J. R. Goodin and D. V. Field (eds.) Plank for Arid Land,.
George Allen and Unwin, London, UK.
Bahri, A. 1987. Utilization of saline waters and soils in Tunisia. Results and
research prospects. FcrNlizere and AgricuBurc 96:17-34.
Barrett-Lennard, E. G., C. V. Malcolm, W. R. Stern and S. M. Wilkins
(eds.~. 1986. Forage and Fuel Production. from Salt Affceted Waetclar~ Elsevier
Publishers, Amsterdam, Netherlands.
Bernstein, L. 1964. Salt Toleranec of Plank. USDA Bulletin No. 283, Washington,
DC, US.
Boyko, H. 1966. Salinity and Aridity. New Approachce to Old Problc~ru. Dr. W. Junk,
Publisher, The Hague, Netherlands.
Epstein, E. 1985. Salt tolerant crops: origins, development, and prospects of
the concept. Plard and Soil 89:187-198.
Epstein, E. 1983. Crops tolerant of salinity and other stresses. Pp. 61-82 in:
Better Crops for Food. Pitman Books, London, UK.
Epstein, E., J. D. Norlyn, D. W. Rush, R. W. Kingsbury, D. B. Kelley, G. A.
Cunningham and A. F. Wrona. 1980. Saline culture of crops: a genetic
approach. Science 210:399-404.
Flowers, T. J., M. A. Haiibagheri and N. J. W. Clipson. 1986. Halophytes. The
Quarterly Rctnew of Biology 61~3~:313-337.
Gallagher, J. L. 1985. Halophytic crops for cultivation at seawater salinity. Plant
and Soil 89:323-336.
Glenn, E. P. and J. W. O'Leary. 1985. Productivity and irrigation requirements
of halophytes grown with seawater in the Sonoran Desert. Journal of Arid
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Goodin, J. R. and D. K. Northington. 1979. Arid Land Plant Rceourecs. Texas
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Greenway, H. and R. Munns. 1980. Mechanisms of salt tolerance in nonhalo-
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Iyengar, E. E. R. 1982. Research on seawater irriculture in India. Pp. 165-175
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Press, New York, New York, US.
Mans, E. V. 1986. Crop tolerance to saline soil and water. Pp. 205-219 in: R.
Ahmad and A. San Pietro (eds.) Prospects for Bio~alinc Rcecarch. University
of Karachi, Karachi, Pakistan.
Miyamoto, S., J. Moore and C. Stichler. 1984. Overview of saline water irrigation
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9
Mudie, P. J. 1974. The potential economic uses of halophytes. Pp. 565-597 in:
R. J. Reimold and W. H. Queen (eds.) Ecology of Halophytca. Academic
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Pasternak, D. 1987. Salt tolerance and crop production a comprehensive
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Pasternak, D. and A. San Pietro (eds.~. 1985. Biosalinity in Action: Bioproduction
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Pasternak, D., A. Danon and J. A. Aronson. 1985. Developing the seawater
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Hoffman, W. J. Alves, R. V. Swain, P. G. Pacheco and R. D. Lemert. 1988.
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Representative terms from entire chapter:
san pietro
