D. Pasternak

The development of halophyte-based agriculture: past and present

BACKGROUND Freshwater comprises about a mere 2·5% of total global water, of which approximately two-thirds is locked into glaciers at the polar ice caps and on mountains. In conjunction with this, in many instances irrigation with freshwater causes an increase in soil salinity due to overirrigation of agricultural land, inefficient water use and poor drainage of unsuitable soils. The problem of salinity was recognized a long time ago and, due to the importance of irrigated agriculture, numerous efforts have been devoted towards improving crop species for better utilization of saline soils and water. Irrigating plants with saline water is a challenge for practitioners and researchers throughout the world. SCOPE Recruiting wild halophytes with economic potential was suggested several decades ago as a way to reduce the damage caused by salinization of soil and water. A range of cultivation systems for the utilization of halophytes have been developed, for the production of biofuel, purification of saline effluent in constructed wetlands, landscaping, cultivation of gourmet vegetables, and more. This review critically analyses past and present halophyte-based production systems in the context of genetics, physiology, agrotechnical issues and product value. There are still difficulties that need to be overcome, such as direct germination in saline conditions or genotype selection. However, more and more research is being directed not only towards determining salt tolerance of halophytes, but also to the improvement of agricultural traits for long-term progress.

Irrigation with brackish water under desert conditions VII. Effect of time of application of brackish water on production of processing tomatoes (Lycopersion esculentum Mill.)

Abstract Processing tomatoes, cv. VFM 82-1-8, were sown in the field and irrigated from the outset with water having electrical conductivities of 1.2 (control), 4.5 and 7.5 dS/m, or were irrigated from the outset with 1.2 dS/m water and then transferred at the four or eleven-leaf stage to irrigation with 4.5 or 7.5 dS/m water. The total yield of fruit in the control was 13.6 kg per 10 m2 and the marketable yield 12.1 kg per 10 m2. When tomatoes were irrigated from the outset with saline water with an electrical conductivity of 7.5 dS/m, the total yield was reduced by 60% relative to the control. However, when saline water irrigation started at the appearance of the fourth or the eleventh leaf, a water salinity of 7.5 dS/m reduced the yield by only about 30%. Salinity increased the acidity, electrical conductivity, and total dissolved solids of tomato fruit. Irrigation with saline water resulted in three- and 1.5-fold increases, respectively, in the sodium and chlorine concentrations in tomato leaves, while the leaf potassium content did not change. A water salinity of 7.5 dS/m did not markedly affect the osmotic potential (π) of tomato leaves up to 77 days after sowing, but decreased it towards the end of the season. Salinity decreased the water potential (ψ) of young tomato plants (27 days after sowing) but had no effect on ψ of 77-day-old plants.

Irrigation with brackish water under desert conditions IX. The salt tolerance of six forage crops

Abstract The response of six forage crops to salinity was investigated in the field by means of a double-line source experimental design. The crops were Rhodes grass ( Chloris gayana Kunth) cv. common, Bermuda grass ( Cynodon dactylon L. Pers.) cv. Suwannee, Kallar grass ( Leptochloa fusca L. Kunth), salt (spike) grass ( Distichlis spicata L.), seashore paspalum ( Paspalum vaginatum Swartz), and alfalfa ( Medicago sativa L.) cv. Gilboa. The trial was carried out over two growing seasons, 1990 and 1991. The electrical conductivity of the irrigation water (EC i ) ranged from 1.2 to 9.5 dS/m, and the mean seasonal electrical conductivity of the saturated soil paste (EC e ) from 3 to 14 dS/m. The salt tolerance of the six forage species was found to be: salt grass > Bermuda grass > seashore paspalum > Rhodes grass > Kallar grass = alfalfa. In the first season, dry matter yields of salt grass, Bermuda grass and seashore paspalum were not affected by a soil EC e of 14 dS/m. In the second season, only the yield of salt grass was unaffected. Rhodes grass had, in the second season, exceptionally high annual yields (5.0 kg/m 2 ) with fresh water irrigation. Thus, even though in comparison with most other grasses the yield of Rhodes grass was reduced by salinity (about 6% yield reduction with every unit increase in EC e above a threshold of 4.0 dS/m), its yield exceeded that of most species at an EC e of 8 dS/m. There was no consistency in the effect of salinity on crude protein, fiber and ash contents among the six forage grasses. In the second season ash content varied from 8% for Bermuda grass to about 15.5% for seashore paspalum. Crude protein content varied from ∼11.5% for Rhodes grass to ∼16% for Bermuda grass and 22% for alfalfa. Both Bermuda grass and salt grass had a relatively high fiber content (40–42%). When brackish water supply was limited, dry matter yield of salt grass was double the yield of the other species, indicating an advantage of this species under non-irrigated rangeland conditions. This work shows that brackish water with an EC i of≥10 dS/m may be used for irrigation of certain forage crops without any yield reduction.

Irrigation with brackish water under desert conditions II. Physiological and yield response of maize (Zea mays) to continuous irrigation with brackish water and to alternating brackish-fresh-brackish water irrigation

Abstract The physiological behavior and yield response of maize under irrigation with saline water was studied in the laboratory and in the field. In the laboratory, the germination rate decreased only when the electrical conductivity (EC) of the substrate solution was above 17 dS/m. The osmotic potential of germinating maize seedlings decreased in proportion to the decrease in osmotic potential of the substrate. In the field, two maize cultivars (a field maize and a sweet maize) were irrigated alternately with saline (11 days from sowing), fresh (21 days from emergence), and saline (from day 33 to harvest) water and compared with maize irrigated with saline water continuously throughout the season. Four levels of irrigation water salinity were used (EC i = 1.2, 4.5, 7.0 and 10.5 dS/m). In the field no osmotic adjustment by the leaf sheaths of plants in response to salinity was observed. The osmotic potential of corn leaf sheaths (π) decreased with ontogeny in all treatments. The midday leaf water potential ( ψ L ) in maize irrigated with 10.5 dS/m water was 0.75 MPa lower than in plants irrigated with 1.2 dS/m water. In the continuous treatment grain yield was reduced significantly with each increase in salt concentration, and the relationship between relative yield ( y ) and EC i could be expressed as y = 100−8.7 (EC i -0.84). With alternating irrigation and 7.0 dS/m treatment the grain yield was the same as in the low EC treatment (6.98 kg/m 2 ).

Irrigation with brackish water under desert conditions XI. Salt tolerance in sweet-corn cultivars

Abstract The salt tolerance of 14 sweet corn ( Zea mays L.) cultivars differing in days for silking and days for grain filling was evaluated under field conditions in an arid environment. Plants were drip irrigated with fresh (EC i =1.2 dS m −1 ) and brackish (EC i =6.2 dS m −1 ) water. Brackish water irrigation started 20 days after planting following the application of 100 mm of fresh water. There were large intraspecific variations in absolute yield and in salt tolerance (expressed as the ratio of brackish water yield to fresh water yield). The cultivar N.K Rogers 2572 had, under saline conditions, both the highest absolute ear yield (18.1 kg per 10 m 2 ) and the highest relative ear yield (82%). Salinity affected all major yield parameters (number of ears per unit area, number of kernels per ear and kernel weight). Ear number was more affected than other parameters. Results indicate that early flowering cultivars are, under the irrigation regime employed in the trial, more salt tolerant than late flowering cultivars. Salinity had an inconsistent effect on kernel quality parameters. In some cultivars it increased soluble carbohydrates and sucrose contents, while in others these parameters were reduced.

Irrigation with brackish water under desert conditions IV. Salt tolerance studies with lettuce (Lactuca sativa L.)

Abstract In a field trial, three Romaine lettuce cultivars and seven iceberg lettuce cultivars were drip irrigated from day 20 after planting with water of four levels of salinity (electrical conductivity of 1.2, 3.5, 8.2 and 10.5 dS/m). The Romaine lettuce cultivars were far more tolerant to salinity than the iceberg cultivars. There were no specific salt-tolerant cultivars within either of the two cultivar groups. The slope of the linear regression of relative yield vs. salinity was −5.6 for the iceberg lettuce cultivars, which is half the value reported elsewhere for lettuce. Iceberg lettuce appears to be more sensitive to salinity at later than at early growth stages. There was no apparent osmotic adaptation of lettuce to salinity. The osmotic potential of the leaves decreased to −1.3 MPa about a month after planting and then gradually increased to −0.6 MPa.

Analysis of phenotypic and genetic polymorphism among accessions of saltgrass (Distichlis spicata)

Morphological and genetic analyses were applied on 37 saltgrass (Distichlis spicata) accessions collected from distant locations throughout the American continent in order to: 1) develop and identify morphologic and genetic profiles for the saltgrass genotypes; 2) characterize the genetic distance among saltgrass accessions within the given germplasm collection; and 3) identify a possible linkage between patterns of genetic and eco-geographical parameters. Analysis based on 70 RAPD markers revealed broad polymorphism among the genotypes and enabled their individual characterization. A UPGMA dendrogram clustered the genotypes into groups according to a general pattern of their geographical origin. Yet, only the group of Californian accessions was significantly distinct from other groups, as determined by χ2 tests. Various statistical analyses indicated that only minor genetic differences existed between seashore and desert saltgrass genotypes, supporting that these two eco-geographical types belong to the same species, Distichlis spicata. Our results suggest that genetic interactions exist between geographically distant saltgrass populations, in spite of the dominance of clonal reproduction in this species. The contribution of dioecy, seed production, and epizoochory to the distribution patterns of saltgrass is discussed at the geographic and at the genetic levels.

Irrigation with brackish water under desert conditions. I. Problems and solutions in production of onions (Allium cepa L.).

Abstract To identify the problems and suggest solutions for onion production under brackish water irrigation in a desert environment, a series of trials with brackish water (electrical conductivity, EC i = 4.4 dS/m) and fresh water (EC i = 1.2 dS/m) was conducted, using both sprinkler and drip irrigation systems. Under sprinkler irrigation with brackish water the mean electrical conductivity of the saturated soil extract ( EC e ) was about 6.0 dS/m and the yield reduction was 60%. With drip irrigation, the EC e under the drippers was about 5.0 dS/m and the yield reduction was 30%. Sprinkler irrigation affected yield through a reduction in both bulb size and bulb number per unit area. Drip irrigation affected the bulb number only. In the latter system seedling death occurred during the first 40 days following field emergence. Yield reduction was completely prevented by germinating and establishing the field with freshwater irrigation before transferring to brackish water irrigation, 45 days after sowing. With the sprinkler system, onion yield with brackish water irrigation could be increased by either increasing the sowing density or by alternating between brackish and fresh water irrigation.

Irrigation with brackish water under desert conditions VI. Automated systems to produce a range of salt concentrations in irrigation water for experimental plots

This paper describes three different systems developed recently in the Negev desert to enable the carrying out of both small- and large-scale field trials on irrigation with brackish and saline water. All three systems are fully automated. The first system, called the mixing junction, was designed to supply to the field relatively large quantities of water with a predetermined, constant salt concentration, when the salinity level of the water source at the field head may vary. The system has an electrical conductivity (EC) sensor inserted after the mixing junction and connected to an electronic logic circuit that operates hydraulic valves for brackish and fresh water in opposite directions to obtain the desired EC level. The second system, called the brine injection system, was developed to produce a range of salt solutions for field studies of salinity when the major water source is of a low and constant salinity level. The system is based on the injection of different amounts of brine simultaneously into several irrigation lines with a water-driven fertilizer pump, through a series of water flow regulators. The third system, called the mixing manifold, was developed to dilute an abundant source of water having a high and constant salinity level with fresh water, to obtain a range of salt concentrations in the irrigation water. The two water sources pass through parallel flow regulators and are mixed at the outlet of the regulators. Water flow through the regulators is controlled by an irrigation computer. All these systems have been operating successfully for periods of from 2 to 5 years.

Irrigation with brackish water under desert conditions. VIII. Further studies on onion (Allium cepa L.) production with brackish water

Abstract The interactions between the effects of salinity and temperature on germination of onion seeds, the effect of stage of salinization on onion yield, possible varietal differences in salt tolerance, and the effect of salinity on water and ion relationships of the plants were studied in laboratory and field experiments. Strong interaction was found between the effects of salinity and temperature on onion germination. At 12°C onion seeds germinated fully in vitro with water having an electrical conductivity ( ec ) of up to 30 dS/m. At 30°C germination was almost completely arrested by an ec of 20 dS/m. Lower temperature and higher salinity both reduced the overall rate of onion germination. In the field, continuous drip irrigation of onion with water having electrical conductivities of 1.2, 4.0, 6.0 and 8.0 dS/m resulted in severe die-off seedlings in the salinized plots during the first 90 days of growth and, consequently, in severely reduced yield of bulbs (50.08, 28.35, 4.12 and 0.44 kg/10 m2, respectively). Much of this effect could be averted by delaying salinization until the 2nd-leaf stage and even more by waiting until the 5th-leaf stage. Nine onion cultivars having broad genetic diversity were subjected to the same salinity treatments. No differences were found in the relative responses of the cultivars to salinity. Observations of plant physiological behavior under saline conditions were used to support explanations for the effects of brackish water irrigation on onion yield.