Rubber production of salt-stressed guayule at various plant populations

Summary The hypothesis that increasing the plant population of guayule (Parthenium argentatum) to compensate for the reduced plant canopy size caused by soil salinity coupled with an anticipated enchancement of rubber production under the moderate environmental stress imposed by salinity was tested in a field plot experiment in the Imperial Valley of California. Irrigation waters having electrical conductivities (EG _i ) of 1.2, 3.2, 6.5, and 9.4 dS/m were applied for 4 years to plots having plant populations of 28,000, 56,000, and 84,000 plants per hectare. The influence of salinity on rubber and resin production was independent of plant population. The salt tolerance threshold, maximum average salinity level of the root zone measured as the electrical conductivity of saturated soil extracts ( ) without yield reduction, was 7.5 dS/m; beyond this threshold, rubber production was reduced 6.1% per unit increase of soil salinity. The salinity values were averaged through the root zone from planting to harvest. The average rubber content — 7.9% — was altered little by treatment or harvest age for 2- to 4-year-old plants. Resin content averaged 8.4% but increased salinity and increased plant population increased the resin content slightly in some cases. Dry matter production of shoots for the nonsaline treatment was 259 kg/ha/month for pollarded (clipped) shoots after 31 months, 203 kg/ha/month for shoots harvested after 43 months, and 401 kg/ha/month for the 24-month period after pollarding. Combining the shoot mass after 31 and 55 months gave an average growth rate of 321 kg/ha, supporting the recommendation for pollarding. Monthly growth rates for the lowest salt treatment (3.2 dS/m) were about 10% less than for the nonsaline treatment (1.2 dS/m). The hypothesis tested was proven to be false because neither increased salinity nor increased plant population increased rubber production.     

Water quantity and quality requirements of guayule: Current assessment

Because of the stragetic and industrial importance of natural rubber, there is renewed interest in cultivating guayule (Parthenium argentatum) in the Southwestern U.S.A. and several other arid regions of the world. This review was made to assess the quantity and quality of water required to cultivate this crop under irrigation. Data from Arizona and West Texas show that under high transplant densities (44 000 to 54 000 plants per ha), shrub and rubber yields increase almost linearly with increasing irrigation up to 300 cm for the first 2 years. The amount of water required to produce a ton of dry shrub in 2 years ranges from 1200 to 1600 m₃ for a wide range of irrigation regimes and irrigation water salinity. Although rubber content in the shrubs increases with increasing water stress, the increase is generally insufficient to offset the reduction in shrub yield under high plant densities. Salinity stress may increase rubber content slightly, but reduces shrub and rubber yields when salinity of irrigation water exceeds 4 to 6 dS m^?1 in sandy soils. The amount of water required to produce 1 kg of rubber with existing cultivars (with rubber contents of 40 to 70 g kg^?1) ranges from 20 to 30 m³, and should decrease substantially with the development of cultivars with higher rubber contents. The resin content in the shrubs does not change greatly with irrigation or salinity levels, thus the resin yield increases proportionally with shrub yield or irrigation amount. If guayule is to be established through direct seeding, additional water of low salinity needs to be allocated. Nursery grown seedlings have been transplanted successfully in spring months with 10–25 cm of water having salinity less than about 4 dS m^?1. If high rubber yields are to be achieved in 2–3 years, water requirements for guayule would be comparable to those for alfalfa. However, guayule can be grown with less quantities of water because of its high drought tolerance, especially when rubber production is the sole purpose.     

A model of crop yield response to irrigation water salinity: theory,testing and application

A relationship between crop yield and irrigation water salinity is developed. The relationship can be used as a production function to quantify the economic ramifications of practices which increase irrigation water salinity, such as disposal of surface and sub-surface saline drainage waters into the irrigation water supply system. Guidelines for the acceptable level of irrigation water salinity in a region can then be established. The model can also be used to determine crop suitability for an irrigation region, if irrigation water salinity is high. Where experimental work is required to determine crop yield response to irrigation water salinity, the model can be used as a first estimate of the response function. The most appropriate experimental treatments can then be allocated. The model adequately predicted crop response to water salinity, when compared with experimental data.Abbreviations A Crop threshold rootzone salinity in Equation of Maas and Hoffman (dS/m) - B Fractional yield reduction per unit rootzone salinity increase (dS/m)^–1 - C_i Average salinity of applied water (dS/m) - C_r Average salinity of rainfall (dS/m) - C_s Linearly averaged soil solution salinity in the rootzone (dS/m) - C_se Linearly averaged soil saturation extract salinity in the rootzone (dS/m) - C_w Average salinity of irrigation supply water (dS/m) - C_z Soil solution salinity at the base of the crop rootzone (dS/m) - C Mean root water uptake weighted soil salinity in equation of Bernstein and François (1973) (dS/m) - E_p Depth of class A pan evaporation during the growing season (m) - ET_a Actual crop evapotranspiration during the growing season (m) - ET_m Maximum crop evapotranspiration during the growing season (m) - I The total depth of water applied during the growing season (including irrigation water and rainfall) (m) - K Empirical coefficient in leaching equation of Rhoades (1974) - K_c Crop coefficient for equation of Doorenbos and Pruit (1977) to estimate crop water use - K_y Yield response factor in equation of Doorenbos and Kassam (1974) - LF The leaching fraction - Ro Depth of rainfall runoff during the growing season (m) - R Depth of rainfall during the growing season (m) - W Depth of irrigation water applied during the growing season (m) - Y Relative crop yield - Y_a Actual crop yield (kg) - Y_m Maximum crop yield (kg) - /z Dimensionless depth for equation of Raats (1974), and empirical coefficient for the leaching equation of Hoffman and van Genutchen (1983)     

Water use,growth and rubber yields of four guayule selections as related to irrigation regimes

Summary There has been renewed interest in cultivating guayule (Parthenium argentatum G.) for rubber production. Water use, growth and rubber yields of four guayule selections (593, 11.591, 11 646 and 4265 XF) were evaluated for two years in nonweighing field lysimeters at El Paso, TX. Four irrigation treatments were evaluated; these involved irrigation when about 40, 60 or 90% of available water was depleted, and the fourth treatment was irrigated at 60% depletion using saline water containing 3,300 mg of dissolved salts per liter. Water use for the two year period for these treatments amounted to 219, 147, 96 and 132 cm, respectively, plus biennial rainfall of 32 cm. Shrub and resin yields increased linearly with increasing irrigation, while rubber contents generally decreased with irrigation. Resultant rubber yields were highest under the lowest stress treatment, yielding about 840 kg/ha. Rubber yields with other treatments averaged 560 kg/ha with no significant yield differences among the tested selections. The salt treatment increased rubber contents of the shrubs, but caused reductions in shrub and rubber yields. Guayule plants survived well under low soil moisture, but water requirement to produce unit quantities of biomass was high (about 15 cm to produce one ton of dry shrub per ha). Guayule should not be regarded as a low water consuming crop if high yields per land area are to be achieved.Contribution from Texas Agricultural Experiment Station. This project was supported in part by a fund from USDA Latex Commission and Binational Agricultural Research and Development Fund (BARD). The authors are Associate Professor, and Technicians, respectively     

Yield and foliar injury responses of mature plum trees to salinity

Summary The salt tolerance of mature Santa Rosa plum trees was assessed on 20-year-old trees grown in the San Joaquin Valley of California. The experimental design consisted of six levels of irrigation water salinity (electrical conductivities of 0.3 to 8 dS/m) replicated five times with each replication consisting of ten trees. Salinity treatments imposed in March 1984 did not influence tree yields harvested in June 1984. In 1985, the second year of treatments, yield from the highest salt treatment (electrical conductivity of irrigation water, EC _i , of 8 dS/m) was reduced by half; the number of fruit harvested was reduced 40%, and fruit size was reduced significantly. Foliar damage was so severe by the end of 1985 that nonsaline water was applied to the two highest salt treatments (EC _i = 6 and 8 dS/m) in an attempt to restore tree vigor. In 1986 salt effects had become progressively worse on the continuing saline treatments. A linear piece-wise salt tolerance curve is presented for soil salinity values, expressed as the electrical conductivity of saturated extracts (EC _e ) integrated to a soil depth of 1.2 m over a 2-year period. The salt tolerance threshold for relative yield (Y _r ) based on 3 years of data was 2.6 dS/m and yield reduction at salinity levels beyond the threshold was 31% per dS/m (Y _ir=100 – 31 [EC _e – 2.6]j). Significant foliar damage occurred when leaf chloride concentrations surpassed 200 mmol/kg of leaf dry weight (0.7%). Sodium concentrations in the leaves remained below 10 mmol/kg (0.02%) until foliar damage became severe. This suggests that chloride was the dominant ion causing foliar damage.     

Irrigated guayule — Plant growth and production

Guayule (Parthenium argentatum Gray) has the potential to alleviate future natural rubber shortages and to provide economic benefits to people in arid lands. A study was initiated to obtain information on guayule plant growth and rubber production as influenced by water management and water use. Annual guayule rubber yields from 2-year-old plants were as high as 500 kg/ha for a whole plant harvest and 300 kg/ha for clipped plants cut 100 mm above the ground using present cultivars under a wet irrigation regime in central Arizona. The clipped plants, when allowed to continue growing, will provide another harvest in 1 or 2 years with a cumulative yield that could be greater than a single harvest of 4-year-old plants. Rubber yield from the wet was twice that of the dry irrigation treatment. Plant height, volume and weight, leaf area, and resin yield were also higher on the wet treatment and decreased in a uniform manner from the wet to dry. Conversely, rubber concentration was higher in the drier than in the watter treatments. Rubber concentration was also higher in the branches than in the roots of the plant. Plant biomass was observed to be closely related to plant height, plant volume, or crown diameter in young plants so that biomass production can be predicted from these plant parameters. Seasonal growth and production patterns also indicated optimum whole plant harvest dates would be from February to March or October to November of each calender year.     

A model for conjunctive use of groundwater and surface waters for control of irrigation salinity

Changes in the hydrologic balance in many irrigation areas, including those in the Murray Basin, Australia, have resulted in high watertables and salinity problems. However, where suitable aquifers exist, groundwater pumping and subsequent irrigation application after mixing with surface waters (referred to as conjunctive water use) can control salinity and watertable depth and improve productivity of degraded land. In order to assess where conjunctive water use will successfully control salinity, it is necessary to estimate the effects of pumped groundwater salinity on rootzone salinity. A simple steady rate model is derived for this purpose from mass conservation of salt and water. The model enables an estimate to be made of rootzone salinity for any particular salinity level of the groundwater being used in conjunction with surface water; this enables calculation of the required crop salt tolerance to prevent yield reductions. The most important input parameters for the model are groundwater salinity, the annual depth of class A pan evaporation, the annual depth of rainfall, the salinity of irrigation water, and a leaching parameter. For model parameters nominated in this paper, where groundwater salinity reaches 5 dS/m a crop threshold salt tolerance greater than 1.6 dS/m is required to avoid yield reductions. Where groundwater salinity approaches 10 dS/m, a crop threshold tolerance of 3 dS/m is required. Whilst the model derived indicates that rootzone salinity is sensitive to groundwater salinity, rootzone salinity is insensitive to leaching for leaching fractions commonly encountered (0.1 to 0.4). The insensitivity to leaching means that it could be expected that similar yields could be attained on heavy or light textured soils. This insensitivity also implies that there is no yield penalty from increasing the mass of pumped salt by pumping to achieve maximum watertable control in addition to leaching. The model developed is also used to estimate yield reductions expected under conjunctive use, for any particular levels of groundwater salinity and crop salt tolerance.     

Irrigated guayule — Production and water use relationships

Interest in developing the guayule plant (Parthenium argentatum Gray) as a source of natural rubber has increased in the United States and other countries during the last decade. A comprehensive study was initiated to obtain information on the production and water-use relationships for guayule. Water-use efficiencies for three cultivars after 2 years ranged from 0.70 to 0.85 kg/m³ for dry matter, 0.045 to 0.055 kg/m³ for resin, and 0.03 to 0.04 kg/m³ for rubber production. The dry matter, resin, and rubber yield were shown to be linearly related to evapotranspiration. Large quantities of irrigation water were needed to get high yields in this short period of time. Relating yield and crop stress on a seasonal basis indicated that guayule grown in an arid environment was more sensitive to water stress in the latter than the first half of the year. Although the drought tolerance characteristics of the guayule crop permits flexibility in irrigation scheduling, the irrigation water requirement can be high in order to increase yields and shorten the harvest time to 3 years or less.     

Long term effects of saline irrigation on the yield and growth of mature Williams pear trees

Salt tolerance of mature Williams Bon Cretien pear trees was assessed in a field trial on a duplex, slowly permeable clay loam. The trees were irrigated with a range of salinities; electrical conductivity of irrigation water (EC_w) of 0.2 to 1.4 dS/m by flood for seven years or 0.2 to 2.1 dS/m by microjet sprinklers for nine years. Water-table levels were maintained below 3 m by a groundwater pump. Yield and leaf ion content were assessed during the treatment period. Aspects of growth and physiology were monitored in the 0.2 and 2.1 dS/m microjet treatments during the seventh irrigation season.Soil profile salinities varied between 3.0 and 4.3 dS/m for the most saline flood treatment and from 1.5 to 2.6 dS/m for the most saline microjet treatment. Soil sodicity (sodium absorption ratio) increased during the experiment, reaching a maximum of 9 in the most saline treatments. The salinity treatments caused reduced yields after seven years. In the most saline treatment (EC_w = 2.1 dS/m, microjet-irrigated), yield decreased to about 60 and 50% of the control in the eighth and ninth years, respectively, and 40% of trees were dead in the ninth year. Leaf ion concentrations (in January) of the most saline treatment were at excess levels (>0.1% Cl and >0.02% Na) from 1982 to 1990. There were significant (P<0.01) negative linear relationships between yield in 1990 and leaf Na and Cl, measured both in 1990 and in 1989. During the seventh season of saline irrigation, lateral shoot growth was reduced, leaves and fruit were smaller and leaf fall was earlier in the 2.1 dS/m treatment compared with the control. Dawn and midday water potential and osmotic potential were not significantly affected by saline irrigation. Midday CO₂-assimilation rates (A) and leaf conductance to water vapour diffusion (g) were similar for 2.1 dS/m irrigated and control trees, however there was a trend towards a reduction in A and g of these salt-treated trees late in the irrigation season when leaf Na and Cl had increased to 250 and 240 mM (tissue water basis) respectively.     

Seedling mortality of several crops induced by root,stem or leaf exposure to salts

Summary Seedling mortality caused by excessive salinity is common in establishing furrow-irrigated crops. This study was conducted to evaluate the processes involved and salinity levels leading to seedling mortality in guayule (Parthenium argentatum Gray cv. 593), carrot (Daucus carota L. cv. Imperator-58), chile pepper (Capsicum annuum L. cv. New Mex. 6–4), and tomato (Lycopersicon esculentum Mills cv. Rutgers). Salt accumulation patterns were also evaluated in soil columns subirrigated with waters of 0.8 and 3.9 dS m^–1. Seedlings were first grown for 10 to 16 days in greenhouse pots with water of 0.8 dS m^–1. Upon emergence of the first true leaf, seedling roots, leaves and stems were independently exposed to different levels of salinity (0.8 to 59 dS m^–1) under two diurnal temperature regimes (22–32°C and 24–40°C). When seedling roots were exposed to the saline solutions, mortality was sub stantially greater under the high temperature, and increased greatly at salinity levels of soil solutions exceeding about 5 dS m^–1 in guayule and carrot, and 15 dS m^–1 in tomato and pepper. Mortality caused by leaf exposures to saline spray was greater under the low temperature with higher relative air humidities, and increased greatly when salinity levels of spray solutions exceeded ap 5, 10, 15 and 20 dS m^–1 in guayule, carrot, tomato and pepper, respectively. Physical abrasion of seedling leaves prior to saline water spraying significantly increased mortality. Stem exposure to a thin layer of salted sand having the saturation extract salinity of up to 58 dS m^–1 caused no significant increase in mortality. Soluble salts were accumulated mostly in a soil depth of 0 to 0.5 cm at a rate of 35 dS m^–1 in 3 weeks when subirrigated with water of 3.9 dS m^–1. Under furrow-irrigated conditions, seedling mortality may be induced mainly through leaf and/or root, but not stem, exposure to the salts accumulated at soil surfaces. Leaf-induced mortality can be the most significant process when wind-damaged seedlings are exposed to saline splatters during light showers common to the semi-arid region.Contribution from Texas Agr. Expt. Station, Texas A & M University System. Supported in part by a grant from the Binational Agricultural Research and Development (BARD) fund and the Expanded Research Fund     

Mungbean response to irrigation with waters of different salinities

Summary Experiments were conducted in lysimeters (1985) and field plots (1986) to evaluate changes in soil moisture and salinity status following irrigations with different blends of a saline water, SW (EC_iw = 6.4 dS/m) and non-saline water, NSW (0.3 dS/m) and their effects on the growth and yield of Mungbean (Vigna radiata L. Wilczek). Normalised to the yield of the treatment receiving NSW (100%), relative seed yields (RY) declined to 73, 11 and 3%, respectively, for the treatments receiving SWNSW blends of 12 (2.5 dS/m), 21 (4.7 dS/m) and SW as such. RY increased to 64 and 74% when NSW was substituted for presowing irrigation and 21 SWNSW blend and SW, respectively were used for postsowing irrigations. Due to moderating effect of rainfall (9.8 cm) during the growing season of 1986, valus of RY obtained with 12 and 21 SWNSW blends were 81 and 42% and increased to 96 and 82% when these waters were applied after presowing irrigation with NSW. Irrigation at presowing with non-saline water leached the salts of shallow depths leading to better germination and initial growth. In addition, plants were able to extract greater amounts of water even from deeper soil layers. The RY of Mungbean was related to the weighted time averaged salinity of the 0–120 cm soil depth (EC_e) by RY = 100-20.7 (EC_e-1.8). The study indicated that applying NSW for presowing irrigation to Mungbean is more beneficial than using it after blending with saline water.     

Salt effects on transplant mortality,growth and rubber yields of guayule

Summary Because of the strategic and industrial importance of natural rubber, there has been renewed interest in cultivating guayule (Parthenium argentatum). This study was performed for assessing feasibility of guayule cultivation with waters high in dissolved salts. The test materials included six USDA selections (11591, 11605, 11619, 11646, 12229 and N576), one cultivar (593) and one hybrid (4265XF). Seedlings were grown for l0 weeks in a greenhouse and transplanted in the spring and in the summer into lysimeters (unit surface dimension of 6 x 7 m) containing loamy sand or silt loam. They were grown with simulated irrigation waters having four levels of salinity (0.8, 2.4, 4.6 and 7.2 dSm^–1 with SAR < 13) and an additional water containing 5 mmol L^–1 of Mg at 2.4 dSm^–1. In the spring planting, over 90% of the transplants survived when furrow irrigated weekly with waters of 4.6 dSm^–1 or less. However, transplant growth for the first several months was reduced by half at irrigation water salinity of 4.6 dSm^–1. In the summer planting, several fold increases in mortality and growth reduction occurred. Dry top Shrub yields after the two growing seasons following the spring planting averaged 10 Mg ha^–1 at 0.8 dSm^–1 and declined on the average 15 and 51 % when irrigated with waters of 4.6 and 7.2 dSm^–1 respectively. The amount of water used to produce one ton of dry shrub was 1,600 m³ with waters of 0.8 and 4.6 dSm^–1, and 1,900 m³ with water of 7.2 dSm^–1. The contents of rubber in the shrubs averaged 61 g kg^–1 at 0.8 dSm^–1 and increased to 70 g kg^–1 at 7.2 dSm^–1. whereas resin contents were not affected by the salt treatments. Resulting rubber yields were reduced on the average by 8.5 and 44% at 4.6 and 7.2 dSm^–1. respectively, because of the reduction in shrub yields. Selection N576 produced the largest rubber yields with the highest rubber content at all levels of salinity. Increasing Mg concentrations from 0.5 to 5 mmol L^–1 in the irrigation waters reduced neither yields nor transplant survival. Yield reductions observed here appeared to be related to Na, but not Mg.Contribution from Texas Agricultural Experiment Station. Supported in part by a grant from the Latex Commission, USDA and by the US-Israel Binational Agricultural Research and Development (BARD) fund     

The effect of saline irrigation water on “Shamouti” orange trees

Summary An irrigation experiment with water of different salinities (2.8, 7.6 and 12.7 mol Cl m^–3) was carried out from 1982 to 1988 in a mature Shamouti orange grove in the coastal plain of Israel. Seasonal accumulation of salts in the soil solution of the root zone (EC of more than 4.0 dS m^–1 at the end of the irrigation season) was almost totally leached during the winter. The average annual rainfall of 550 mm reduced EC values below 1.0 dS m^–1. Tree growth, as measured by the increase in cross sectional area of main branches, was retarded by saline irrigation water (123, 107 and 99 cm² growth per tree during six years for the 2.8, 7.6 and 12.7 mol Cl m^–3 treatments, respectively). Potassium fertilization (360 kg K₂O ha^–1) increased yield at all salinity levels during the last three years of the experiment, mainly by increasing fruit size. Saline irrigation water slightly increased sucrose and C1 concentrations in the fruit juice. Salinity decreased transpiration, increased soil water potential before irrigation and decreased leaf water potential. However, the changes in leaf water potential were small. Leaf Cl and Na concentrations increased gradually during the experimental period, but did not reach toxic levels up to the end of the experiment (4.4 g Cl kg^–1 dry matter in the high salt treatment vs. 1.7 in the control). Relatively more leaf shedding occurred in the salinized trees as compared to the control. The sour orange root-stock apparently provided an effective barrier to NaCl uptake; therefore, the main effect of salinity was probably osmotic in nature. No interactions were found between N or K fertilization and salinity. Additional N fertilization (160 kg N ha^–1 over and above the 200 kg in the control) did not reduce Cl absorption nor did it affect yield or fruit quality. Additional K had no effect on Na absorption but yield and fruit size were increased at all salinity levels. No significant differences were obtained between partial and complete soil surface wetting (30% and 90% of the total soil area resp.) with the same amounts of irrigation water. The effect of salinity on yield over the six years of the experiment was relatively small and occurred only after some years. But, in the last three years salinity significantly reduced average yields to 74.6, 67.1, and 64.2 Mg ha^–1 for the three levels of salinity, respectively.These results suggest that saline waters of up to 13 mol Cl m^–3 primarily influence the tree water uptake and growth response of Shamouti orange trees, whereas yield was only slightly reduced during six years.     

Long term use of saline water for irrigation

Use of saline drainage water in irrigated agriculture, as a means of its disposal, was evaluated on a 60 ha site on the west side of the San Joaquin Valley. In the drip irrigation treatments, 50 to 59% of the irrigation water applied during the six-year rotation was saline with an EC_w ranging from 7 to 8 dS/m, and containing 5 to 7 mg/L boron and 220 to 310 g/L total selenium. Low salinity water with an EC_w of 0.4 to 0.5 dS/m and B 0.4 mg/1 was used to irrigate the furrow plots from 1982 to 1985 after which a blend of good quality water and saline drainage water was used. A six-year rotation of cotton, cotton, cotton, wheat, sugar beet and cotton was used. While the cotton and sugar beet yields were not affected during the initial six years, the levels of boron (B) in the soil became quite high and were accumulated in plant tissue to near toxic levels. During the six year period, for treatments surface irrigated with saline drainage water or a blend of saline and low salinity water, the B concentration in the soil increased throughout the 1.5 m soil profile while the electrical conductivity (EC_e) increased primarily in the upper l m of the profile. Increaszs in soil EC_e during the entire rotation occurred on plots where minimal leaching was practiced. Potential problems with germination and seedling establishment associated with increased surface soil salinity were avoided by leaching with rainfall and low-salinity pre-plant irrigations of 150 mm or more. Accumulation of boron and selenium poses a major threat to the sustainability of agriculture if drainage volumes are to be reduced by using drainage water for irrigation. This is particularly true in areas where toxic materials (salt, boron, other toxic minor elements) cannot be removed from the irrigated area. Continual storage within the root zone of the cropped soil is not sustainable.     

Response of cotton water stress indicators to soil salinity

Summary A field study was conducted on cotton (Gossypium hirsutum L. c.v. Acala SJ-2) to investigate the effects of soil salinity on the responses of stress indices derived from canopy temperature, leaf diffusion resistance and leaf water potential. The four salinity treatments used in this study were obtained by mixtures of aqueduct and well water to provide mean soil water electrical conductivities of 17, 27, 32 and 38 dS/m in the upper 0.6 m of soil profile. The study was conducted on a sandy loam saline-alkali soil in the lower San Joaquin Valley of California on 30 July 1981, when the soil profile was adequately irrigated to remove any interference of soil matric potential on the stress measurements. Measurements of canopy temperature, leaf water potential and leaf diffusion resistance were made hourly throughout the day.Crop water stress index (CWSI) estimates derived from canopy temperature measurements in the least saline treatment had values similar to those found for cotton grown under minimum salinity profiles. Throughout the course of the day the treatments affected CWSI values with the maximum differences occurring in mid-afternoon. Salinity induced differences were also evident in the leaf diffusion resistance and leaf water potential measurements. Vapor pressure deficit was found to indicate the evaporative demand at which cotton could maintain potential water use for the various soil salinity levels studied. At vapor pressure deficits greater than 5 kPa, cotton would appear stressed at in situ soil water electrical conductivities exceeding 15 dS/m. The CWSI was as sensitive to osmotic stress as other, more traditional plant measures, provided a broader spatial resolution and appeared to be a practical tool for assessing osmotic stress occurring within irrigated cotton fields.     

Salinity sensitivity of sorghum at three growth stages

Summary The relative salt tolerance of two sorghum cultivars [Sorghum bicolor (L.) Moench., cvs. Northrup King 265 and Asgrow Double TX] at three different stages of growth was determined in a greenhouse experiment. Plants were grown in sand cultures irrigated four times daily with modified Hoagland's solution. A nonsaline solution and six solutions salinized with NaCl and CaCl₂ (2: 1 molar ratio) provided treatments with osmotic potentials (_s) ranging from –0.05 to –1.05 MPa. The saline treatments were imposed for 30 days beginning at either Stage 1, 4, or 7 as defined by Vanderlip and Reeves (Agron J. 64:13, 1972). The 30-day stages are referred to here as the vegetative, reproductive and maturation stages although the first stage may have included initial panicle differentiation. Both cultivars were most sensitive to salinity during the vegetative stage and least sensitive during maturation. Based on a nonlinear least-squares analysis, grain yield reductions of 50% were predicted at _s=–0.68, –1.02, and –1.14 MPa for NK265 and at –0.62, –1.00, and –1.10 MPa for Double TX when salinized during the vegetative, reproductive, and maturation stages, respectively. Although salinity had no significant effect on mean kernel weights, significant growth stage effects and interaction indicated that kernels were heaviest for plants salinized during the vegetative stage. Stover yields were significantly reduced by salination during the vegetative stage but were unaffected when plants were salinized during the maturation stage. Salination during the reproductive stage also decreased stover yield of Double TX but the effect was smaller than that during the first stage. Stover yield of NK265 was unaffected by salinity at this stage.Mineral analysis of the first leaf below the flag leaf at harvest indicated that both cultivars tended to exclude Na from the upper leaves. Ca and Cl concentrations increased with increased salinity in plants salinized during the maturation stage but salination in earlier stages decreased Ca concentration of this upper leaf at harvest and had no effect on the final Cl concentration. Phosphate and K concentrations decreased when plants were salinized during the third stage but increased when plants were salinized during the vegetative and reproductive stages. Mg was unaffected by salinization during the first and last stage but decreased when plants were salinized,during the reproductive stage. An extensive data base now exists which describes the salt tolerances of many different crops (Maas and Hoffman 1977; Maas 1986). These data express yield responses as a function of the average salt concentration in the rootzone. Generally, these data apply only if salinity is fairly uniform from the seedling stage to maturity. Except for germination, little information exists on the tolerances of crops at different stages of growth. Such information could be invaluable to optimize the use of limited water resources. Knowledge that crops are more tolerant during some stages of growth will improve new strategies for utilizing saline drainage waters (Rhoades 1984).Several studies indicate that tolerances do change as the crop develops and matures, but none of these studies completely separated the effects of duration of treatment from the stage of growth that the crop was treated (Ayers et al. 1952; Kaddah and Ghowail 1964; Kovalskaia 1958; Lunin et al. 1961 a, 1961 b; Maas et al. 1983; Ogo and Sasai 1955; Piruzyan 1959; Verma and Bains 1974). Comparisons of sensitivity during specific phenological stages are confounded when treatment periods are of unequal duration.This study was initiated to determine the sensitivity of grain sorghum [Sorghum bicolor (L.) Moench] to salinity during three 30-day periods of growth. Francois et al. (1984) recently reported that sorghum is a moderately salt-tolerant crop. In field plot tests, grain yields of two cultivars decreased 16% per unit increase in salinity (electrical conductivity of saturated soil extracts from the rootzone) above 6.8 dS/m. They further reported that both cultivars were significantly more tolerant at germination than at later stages of growth. Soil water salinities above 8.2 dS/m delayed germination but full germination occurred within 10 days at salinities up to 22 dS/m. Treatments in the present study were designed to assess plant growth and yield responses to 30-day exposures to salinity beginning at either the 2-leaf stage, at the beginning of rapid culm elongation, or after anthesis.     

Effects of drip irrigation with saline water on waxy maize (Zea mays L. var. ceratina Kulesh) in North China Plain

In order to study the effects of drip irrigation with saline water on waxy maize, three years of field experiments were carried out in 2007-2009 in North China Plain. Five treatments with average salinity of irrigation water, 1.7, 4.0, 6.3, 8.6, and 10.9 dS/m were designed. Results indicated that the irrigation water with salinity <10.9 dS/m did not affect the emergence of waxy maize. As salinity of irrigation water increased, seedling biomass decreased, and the plant height, fresh and dry weight of waxy maize in the thinning time decreased by 2% for every 1 dS/m increase in salinity of irrigated water. The decreasing rate of the fresh ear yield for every 1 dS/m increase in salinity of irrigation water was about 0.4-3.3%. Irrigation water use efficiency (IWUE) increased with the increase in salinity of irrigation water when salinity was <10.9 dS/m. Precipitation during the growing period significantly lightened the negative impacts of irrigation-water salinity on the growth and yield. Soil salinity in depth of 0-120 cm increased in the beginning of irrigation with saline water, while it was relatively stable in the subsequent year when salinity of irrigation water was not higher than 4.0 dS/m and the soil matric potential (SMP) at 0.2 m directly underneath the drip emitter was controlled above −20 kPa.     

Combined effects of KNO3 and salinity on yield and chemical composition of lettuce and Chinese cabbage

Summary The effect of N and K nutrition on the salt tolerance of lettuce (Lactuca saliva L. cv. Saunas) and Chinese cabbage (Brassica campestris L., Pekinensis cv. Kazumi) was evaluated in three greenhouse experiments under a controlled aero-hydroponic system of cultivation. Three levels of KNO₃ (1, 5 and 10 mM) were tested in all the experiments with rapidly circulated saline and nonsaline nutrient solutions. Two experiments, carried out between January and March 1989, with lettuce (Exp. I) and Chinese cabbage plants (Exp. III), consisted of two salinity levels, EC = 1.75 and 6.0 dS m^–1, the former representing a nonsaline nutrient solution. In the third experiment with lettuce (Exp. II., conducted between March and May 1989), three saline nutrient solutions having EC levels of 4.7, 7.75 and 10.75 dS m^–1 were compared to the nonsaline solution. The nutrient solutions were salinized with NaCl and CaCl₂, in a 4:1 molar ratio. The highest yields of fresh weight of both crops were obtained from the 5 mM KNO₃ under both saline and non-saline conditions. The 10 mM treatment caused yield reduction in Chinese cabbage, probably due to a severe tipburn disorder. The relatively high fresh weight yield obtained at the lowest (1 mM) KNO₃ level can be explained by the positive effect of circulation velocity on nutrient uptake. The threshold salinity damage value for the vegetative yield of lettuce plants fed by 5 or 10 mM KNO₃ was approximately 5 dSm^–1 and the yield decreased by 6.5% per unit dS m^–1 above the threshold. No yield improvement due to the addition of KNO₃ occurred under highly saline conditions (Exp. II). The fresh weight of Chinese cabbage obtained from the saline 1 and 5 mM KNO₃ treatments was approximately 15% lower than the non-saline-treatment (Exp. III). Salinity increased tipburn and the effect was not altered by the addition of KNO₃. No significant interaction between nutrition (KNO₃ level) and salinity was found. The application of salts increased the concentration of Na and Cl in plant tissue and reduced the levels of N and K; the opposite occurred in plants fed by the medium and high levels of KNO₃.Contribution from Institute of Soils and Water, ARO, Volcani Center, PO Box 6, Bet Dagan 50250, Israel. No. 3092-E 1990 series     

Effect of initial soil salinity and subirrigation water salinity on potato tuber yield and size

A field lysimeter study was conducted to investigate the effect of initial soil salinity and salinity level of brackish subirrigation water on tuber weight and tuber size of three potato (Solanum tuberosum L.) cultivars (Kennebec, Norland and Russet Burbank) under simulated arid conditions. Both saline and non-saline initial soil conditions were simulated in a total of 36 lysimeters. Eighteen lysimeters were flushed with fresh water (0.2 dS/m), while the remaining 18 lysimeters were flushed with brackish water (2 dS/m). For each soil condition, two subirrigation water concentrations, 1 and 9 dS/m, were used in nine lysimeters each. For each subirrigation water treatment, three potato cultivars were grown. In all lysimeters, water table was maintained at 0.4 m from the soil surface. Arid conditions were simulated by covering the lysimeter top with plastic mulch, allowing the potato shoots to grow through a cut in the mulch. The average root zone salinities (EC_w) were found to be 1.2 and 1.5 dS/m in non-saline lysimeters subirrigated with 1 and 9 dS/m waters, respectively. The corresponding salinities were 3.2 and 3.7 dS/m in the saline lysimeters. Across cultivars, there was no significant effect of either initial soil salinity or subirrigation water salinity on total tuber weight. However, the weight of Grade A tubers was higher in non-saline soil than in saline soil. Kennebec and Russet Burbank Grade A tuber weights were not affected by the initial soil salinity. On the contrary, a significant reduction in Grade A and total tuber weight under initially saline soil was evident for the Norland cultivar.     

Drip irrigation with saline water for oleic sunflower (Helianthus annuus L.)

The field experiments were carried out in 2007 and 2008 to study the effects and strategies of drip irrigation with saline water for oleic sunflower. Five treatments of irrigation water with average salinity levels of 1.6, 3.9, 6.3, 8.6, and 10.9 dS/m were designed. For each treatment, 7 mm water was applied when the soil matric potential (SMP) 0.2 m directly underneath the drip emitters was below −20 kPa, except during the seedling stage. To ensure the seedling survival, 28 mm water was applied after sowing during the seedling stage. Results indicate that amount of applied water decreases as salinity level of irrigation water increases. The emergence will be delayed when the salinity level of irrigation water is higher than 6.3 dS/m, but these differences will be alleviated if there is rainfall during emergence period. The final emergence percentage is not changed when salinity level of irrigation is less than 6.3 dS/m, and the percentage decreases by 2.0% for every 1 dS/m increase when the salinity level of irrigation water is above 6.3 dS/m, but the decreasing rate will be reduced if there is rainfall. The plant height and yield decrease with the increase of salinity of irrigation water. The height of plants decreases by 0.6-1.0% for every 1 dS/m increase in salinity level of irrigation water. The yield decreases by 1.8% for every 1 dS/m increase in salinity level of irrigation water, and irrigation water use efficiency (IWUE) increases with increase in salinity of irrigation water. The soil salinity increases as the salinity of irrigation water increasing after drip irrigation with saline water in the beginning, but the soil salinity in soil profile from 0 to 120 cm depths can be maintained in a stable level in subsequent year irrigation with saline water. From the view points of yield and soil salt balance, it can be recognized even as the salinity level of irrigation water is as high as 10.9 dS/m, saline water can be applied to irrigate oleic sunflower using drip irrigation when the soil matric potential 0.2 m directly under drip emitter is kept above −20 kPa and the beds are mulched in semi-humid area.