Salt sensitivity of cowpea at various growth stages

Summary The relative salt tolerance of cowpea (Vigna unguiculata (L.) Walp. cv. California Buckeye No. 5) at different stages of growth was determined in a greenhouse. Plants were grown in sand cultures that were irrigated four times daily with modified half-strength Hoagland's solution. Salination with NaCl and CaCl₂ (2:1 molar ratio) provided seven treatment solutions with osmotic potentials (_s) ranging from –0.05 to –1.05 MPa (electrical conductivities of 1.4 to 28 dS/m). Salt stress was imposed for 20 days beginning at either 7, 27, or 52 days after planting. The three 20-day stages are referred to here as vegetative, flowering, and pod filling stages. Pod and seed yields from plants stressed during either the vegetative, flowering, or pod-filling stages indicated that cowpea was the most sensitive to salinity during the vegetative stage and became less sensitive the later plants were stressed. Seed yield was reduced 50% at _s =–0.45, –0.76, and –0.88 MPa for plants salinized during the vegetative, flowering, and pod-filling stages, respectively. Salinity reduced seed yield by reducing seed number; it had little, if any, effect on the weight of individual seeds. Vegetative growth was significantly reduced by salt stress during all three stages but the effect was much less when stress was imposed during the last two stages than during the first stage.     

Salt sensitivity of wheat at various growth stages

Summary The relative salt tolerance of two wheat species (Triticum aestivum L., cv. Probred and Triticum turgidum L., Durum Group, cv. Aldura) at different stages of growth was determined in a greenhouse experiment. Plants were grown in sand cultures that were irrigated four times daily with modified Hoagland's solution. Salinization with NaCl and CaCl₂ (2:1 molar ratio) provided seven treatment solutions with osmotic potentials ( _s ) ranging from –0.05 to –1.25 MPa (electrical conductivities of 1.4 to 28 dS/m). Salt stress was imposed for 45 days beginning at either 10, 56, or 101 days after planting. The three 45-day stages are referred to here as the vegetative, reproductive, and maturation stages although the first stage included spikelet differentiation. In a separate experiment, seedling growth was measured after 21 days of salt stress ( _s = –0.05 to –0.85 MPa) initiated at 0, 7, 11, and 16 days after planting. Salt stress ( _s = –0.65 MPa) delayed germination by 4 days for both wheats but full emergence occurred. Relative growth response curves of the seedlings were alike regardless of whether salt stress was imposed at planting or at the 1st, 2nd, or 3rd-leaf stage of growth. Salt stress also retarded leaf development and tillering but hastened plant maturity. Grain yields from plants stressed during either the vegetative, reproductive, or maturation stages indicated that both species became less sensitive to salinity the later plants were stressed. Grain yield was reduced 50% at _s = –0.76, –1.53, and –1.58 MPa for Probred and –0.65, –1.08, and –1.34 MPa for Aldura when salinized during stages 1, 2, and 3, respectively. Salinity reduced grain yield by reducing seed number more than seed weight indicating that salt stress during stage 1 affected spikelet differentiation. Straw yield was significantly reduced by salt stress only during stage 1. Leaf mineral analyses revealed that Aldura readily accumulated Na whereas Probred did not. Both species accumulated Cl but the concentrations were much higher in Aldura. K uptake was severely inhibited by salt stress imposed during the first stage but not when imposed the second stage.     

Timing of salinity stress affects rice growth and yield components

Differential sensitivity during growth stages is one of the major issues in the management of saline water for irrigation. This study was designed to analyze the effects of salinity on plant growth and yield components of rice by composing 20-day periods of salinization at different growth stages. Plants were grown in sand tanks in a greenhouse and irrigated with nutrient solutions. Treatments were three levels of salinity with electrical conductivities at 1.8, 3.2 and 4.6 dS m⁻¹ and five timing treatments. Plants were salinized on the day of seeding, 1-leaf, 3-leaf, panicle initiation (PI), and booting stages, respectively, and stress was relieved after 20 days in each timing treatment. Salinity-induced reductions in shoot dry weights of plants harvested before PI were significant, but there were no significant differences among timing treatments. Reduction in shoot dry weight of plants harvested at seed maturity was significant only when plants were salinized for a 20-day duration before booting, but not after booting. Reduction in tiller number per plant was significant only when plants were salinized for a 20-day duration before PI. The reductions in spikelets per panicle and seed weight per panicle were most pronounced when plants were stressed between the 3-leaf and PI stages or between PI and booting stages and minor when stressed at the other stages. A 20-day period between 3-leaf and PI stages was most sensitive to salinity in terms of seed yield. These results indicate that the differential sensitivity at growth stages can be clearly shown when stages are well defined in the timing treatments and the stress is quantified at growth stages based on the same duration of salinization. The interaction between cultivar and timing treatment was not significant. Uniform management options can be developed for irrigation using saline water for the cultivars with similar genetic backgrounds.     

Salt tolerance of irrigated guayule

Summary The salt tolerance of guayule (Parthenium argentatum Gray cv. N565-II) was tested in small held plots (silty clay soil) in the Imperial Valley of California. Seedlings were transplanted in October 1981. Differential salination was begun in March 1982 and continued for 4 years by irrigating with waters salinized with NaCl and CaCl₂ (1:1 by wt.) to obtain electrical conductivities of 0.8, 1.4, 3, 6, 9, and 12 dS/m. Dry matter, rubber, and resin yields were determined from pollarded plants in February 1984 and uprooted plants in February 1985 and 1986. Rubber concentrations in the woody branches in 1984 and 1985 averaged 6.1 and 7.3%, respectively on a dry weight basis and were not significantly affected by soil salinity. Resin concentrations averaged 8.6% and 7.3% for the two years. In 1986, both rubber and resin concentrations decreased with increased salinity. Rubber and resin concentrations in the root crowns were approximately one percentage point less than those of the shoot. Dry matter and resin yields were not affected by salinity until the time- and depth-averaged electrical conductivity of the saturated-soil extracts ( ) taken from the rootzone (0–90 cm) exceeded 8.7 dS/m. Above 8.7 dS/m, both yields decreased 11.6% per dS/m increase in . Rubber yields decreased 10.8% per dS/m above a threshold of 7.8 dS/m. Plant mortality rather than growth reduction at high levels of salinity appears to be the limiting factor for rubber production from irrigated guayule.     

Reduction in growth and yield of Jerusalem artichoke caused by soil salinity

Summary The salt tolerance of irrigated Jerusalem artichokes (Helianthus tuberosus L.) was assessed in terms of biomass of both above ground parts and tubers in greenhouse and field trials. Salinity of irrigation water ranged from 0.7 to 12 dS m^–1 in the greenhouse trial and from 0.2 to 10 dS m^–1 in the field trial. Yield response of the dry matter of tubers of greenhouse-grown plants and of above ground parts of greenhouse-grown and fieldgrown plants, fell within the moderately tolerant category of Maas and Hoffman (1977). However, tuber yields in the field on a heavy clay loam fell within the moderately sensitive category, described by the equation, Y = 100 – 9.62 (ECe-0.4), where Y = yield (t ha^–1) as a % of that under non-saline conditions and EC_e = electrical conductivity of saturation extract in the rootzone (0–30 cm). The Cl concentration of leaves increased linearly with increasing external salinity and increased from tubers to stems to leaves. In contrast, leaf Na remained low except at the highest salinities, despite consistently higher stem Na; indicating some mechanism for restriction of leaf Na up to a certain external salinity.     

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.     

Leaf,stolon and root growth of white clover (Trifolium repens L.) in response to irrigation with saline water

The effect of irrigation with water at salinity concentrations of 2.6 and 5.2 dS m^–1 on the growth of pure swards of six cultivars of white clover (Trifolium repens L.) was examined over three irrigation seasons at Tatura, Victoria, Australia. After two irrigation seasons, soil EC _e levels increased to 6 dS m^–1 at 0–60 cm depth in the higher salinity treatment resulting in highly significant (p < 0.001) reductions in shoot dry matter production, flowering densities and petiole and stolon densities. These saline conditions also increased (p <0.001) concentrations of Cl and Na in the shoots and reduced (p < 0.001) leaf water potentials and canopy photosynthetic efficiency rates especially at high temperatures. In contrast, root growth increased at shallow depths (0–15 cm) under both saline irrigation treatments (p <0.001). Cultivars differed significantly in salt tolerance (p < 0.001), with cultivars Haifa and Irrigation exhibiting superior tolerance in terms of lower reductions in herbage yield (p <0.05) and petiole densities (p <0.001) during one irrigation season and lower concentrations of Na and Cl in the shoots (p <0.05) compared with the other four cultivars (Aran, Kopu, Pitau and Tamar). In addition, canopy photosynthetic efficiency rates (A ^*) in plots irrigated with water at 5.2 dS m^–1 were higher in cultivar Haifa compared with cultivar Tamar (p <0.05). The salt tolerance ranking obtained for the six cultivars was in broad agreement with earlier greenhouse studies. Consequently, it appears that, while white clover is an extremely salt-sensitive species, it is possible to grow cultivars which display greater salt tolerance than other cultivars and which provide some scope to increase, or at least to maintain, pasture yields in areas where the soil salinity is low to moderate or where pumped saline groundwater is re-used for Irrigation.     

The effect of water salinity on growth and physiological stages of eight Canola (Brassica napus) cultivars

Laboratory/greenhouse and field experiments were conducted to evaluate the effects of salinity levels ranging from 1 to 12 dS/m on germination rate, 8 leaf seedling dry matter, seed yield, and seed oil content of the 8 Canola (Brassica napus) cultivars: ACSN1, Falcon, Shirali, Ceres, Tower, Cobra, Global, and Oyerka. Statistical results revealed that the factors: salinity, cultivar, and their interaction had significant (P<0.01) effect on germination rate and 8 leaf seedling dry matter. Based on statistical analysis seed yield was significantly influenced by both salinity and cultivar at the 5% significance level; while the cultivar factor had a significant effect on seed oil content, salinity did not show any effect on seed oil content. Analytical results, using the well-known sigmoid or S-shape salinity response function gave reliable results for determining tolerant and sensitive cultivars to salinity. Applying an existing model on canola response to salinity levels in different growth stages, the values of C ₅₀ and P parameters were developed for local canola cultivars. Results showed that the response of cultivars to salinity levels vary in different growth stages. While a cultivar is tolerant in a growth stage, it may be sensitive to salinity in another growth stage. Based on observed data and ANOVA analysis, we concluded that ACSN1, Shiraly, and Falcon can be ranked as salt-tolerant, and Global and Oyerka as the salt-sensitive cultivars.     

Water tension thresholds for processing tomatoes under drip irrigation in Central Brazil

Drip irrigation has the potential to save water and mitigate foliar diseases for processing tomato production in Central Brazil. Four experiments were carried out at Embrapa Vegetables, Brasília, Brazil, to establish irrigation management strategies during vegetative, fruit development, and maturation growth stages of drip-irrigated processing tomato. Soil water tension (SWT) threshold values ranging from 5 to 120 kPa were evaluated. Plants growing under higher water deficit during the vegetative stage showed root systems up to 10 cm deeper than those irrigated more frequently. Maximum fruit yield was reached when irrigations were performed at SWT thresholds of 35, 12, and 15 kPa during vegetative, fruit development, and maturation growth stages, respectively. Total soluble solids content was not affected by irrigation treatments during vegetative and fruit development stages, but increased as SWT increased during fruit maturation growth stage.

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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     

Maize yield response to deficit irrigation during low-sensitive growth stages and nitrogen rate under semi-arid climatic conditions

Knowledge of crop production in suboptimal environmental conditions not only helps to sustain crop production but also aids in the design of low-input systems. The objective of this study was to evaluate the effects of water stress imposed at low-sensitive growth stages (vegetative, reproductive, and both vegetative and reproductive) and level of nitrogen (N) supply (100 and 200 kg ha⁻¹) on the physiological and agronomic characteristics of two hybrids of maize (Zea mays L.). A two-site field experiment was carried out using a randomized complete block design with three replications and a split-factorial arrangement. A water deficit (WD) was induced by withholding irrigation at different stages of crop development. The results showed that proline content increased and the relative water content, leaf greenness, 100-kernel weight and grain yield decreased under conditions of WD. The highest IWUE was obtained when maize endured WD at vegetative stage at two sites. The limited irrigation imposed on maize during reproductive stage resulted in more yield reduction than that during vegetative stage, compared with fully irrigated treatment. The 100-kernel weight was the most sensitive yield component to determine the yield variation in maize plant when the WD treatments were imposed in low-sensitive growth stages. The results of the statistical regression analysis showed liner relationships between RGR during a period bracketing the V₈ or R₃ stages and 100-kernel weight in all the WD treatments. The increase of N supply improved yield and IWUE when maize plant endured once irrigation shortage at vegetative stage. But, the performance of high N fertilizer reduced and eliminated when water deficit imposed once at reproductive stage and twice at vegetative and reproductive stages, respectively. Furthermore, the response of T.C647 hybrid to increase of N supply was stronger than S.C647 hybrid.     

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     

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)     

Growth of faba bean (Vicia faba L.) as influenced by irrigation water salinity and time of salinization

A greenhouse study was conducted to investigate the response of faba bean (Vicia faba L.) to water salinity applied at different times of salinization. Faba beans were grown on loamy sand in pots and irrigated daily with modified half-strength Hoagland's solution. Salinization of the nutrient solution with NaCI and CaCl₂ (2:1 molar ratio) provided four treatment solutions with electrical conductivities of 2, 6, 10 and 14 dS m⁻¹ and was imposed on the tenth day from planting, and continued until day 30 (T1), from day 30 until day 50 (T2) and from day 50 to day 70 (T3) using a randomized block factorial design with five replications. The results indicated that faba bean was more sensitive to salinity during the vegetative stage and less sensitive at later stages. Water salinity significantly reduced the grain yield and grain number but did not affect grain weight. Vegetative growth decreased significantly by salinity stress during the three salinization periods but was more serious at the first stage.     

Leaching rates under a perennial pasture irrigated with saline water

Summary Dilution of saline groundwater (2.5 dS m^–1) for irrigation is a common practice in the Shepparton Region of Northern Victoria. There is little information describing the leaching rates and hence longterm soil salinity levels that will result from such practices. There is also little information to suggest the effect of irrigating with saline water on groundwater recharge.Leaching rates under perennial pastures grown on a Paleustalf were estimated using three methods based on the mass conservation of chloride. Five treatments were irrigated with water ranging from 0.22 dS m^–1 to 4.84 dS m^–1. Leaching rates were greater the higher the salinity of the irrigation water (Table 3). Increased leaching resulted from both increased electrolyte levels in the water and decreased water uptake by plants.A model based on non-steady state solute movement usefully predicted the approach of steady-state conditions in the root zone several years earlier than simple observation of the solute data allowed (Table 5).     

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.     

微咸水-淡水交替灌溉对玉米生长指标及产量的影响

以隆平206玉米品种为载体进行了温室避雨盆栽试验,试验设计"咸-淡-淡"、"淡-咸-淡"和"淡-淡-咸"3种交替灌溉模式,即分别在壮苗期、拔节期、抽雄—乳熟期3个阶段灌溉微咸水,微咸水矿化度设计为1、3和5 g/L,监测生长生理和产量指标。结果表明,任一时期灌溉矿化度1 g/L微咸水对玉米株高、叶面积、SPAD和产量影响不明显;随微咸水矿化度的增加,玉米受抑制作用增强;微咸水灌溉后壮苗期玉米株高、叶面积、SPAD受影响显著,由于玉米前期补偿生长能力强,随生长推进,壮苗期微咸水灌溉处理与CK间差异逐渐减小,玉米株高、叶面积、SPAD受抑制最显著的为拔节期微咸水灌溉处理,其次是壮苗期,抽雄—乳熟期最小;对玉米产量影响最大的是抽雄—乳熟期微咸水灌溉处理,其次是拔节期,壮苗期影响最小,故生殖生长阶段不宜采用微咸水灌溉;滨海农区可根据淡水、微咸水资源的时空分布特征设计交替灌溉制度,利用淡水灌溉的补偿效应确保玉米产量。     

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.     

The effect of saline irrigation on lucerne production: shoot and root growth, ion relations and flowering incidence in six cultivars grown in northern Victoria, Australia

The effect of irrigation with saline (0.1-7.6 dS m^-1) water on the growth of six cultivars of lucerne was assessed over four irrigation seasons at Tatura, Victoria, Australia. Measurements made in the study included shoot dry matter production, shoot ion concentrations, flowering incidence, root distribution and soil salinity and sodicity levels. After four seasons, soil EC_e levels had risen to 4.2 dS m^-1 at the beginning of the irrigation season and this increased to around 6 dS m^-1 at the end of the season for the highest salinity irrigation treatment (7.6 dS m^-1). The soils in the two most saline irrigation treatments also became sodic (SAR_1:5>3) by the third and fourth seasons. By the second season, cultivars differed significantly in salt tolerance as defined by the rate of decline in dry matter production. The cultivars CUF 101 and Validor were consistently the most salt-tolerant cultivars, although cv. Southern Special produced the greatest amount of dry matter over all salinity treatments. Root densities at depths from 0 to 60 cm were greater under saline (2.5 and 7.6 dS m^-1) than under non-saline conditions (0.1 dS m^-1). Flower production was increased by salinity. It was concluded that, despite the presence of intraspecific variation for salt tolerance, it is detrimental to irrigate lucerne with water at electrical conductivities greater than 2.5 dS m^-1 on a red-brown earth in southern Australia.     

Irrigation of lucerne with saline groundwater on a slowly permeable,duplex soil

Summary Lucerne was irrigated for three years on a slowly permeable, duplex soil, with saline water up to 2.4 dS m^–1 without significant yield decline. Irrigation water of 4.5 dS m^–1 significantly reduced yield. Lucerne yield was most closely related to the soil ECe of the 0–15 cm depth, rather than the total rootzone, and was described by; Relative yield=100–6.5 (ECe-2.1). While lucerne roots reached depths of at least 150 cm, approximately 80% of total root length was located in the 0–60 cm depth.Increasing salinity increased the plant concentrations of sodium and chloride, however, these changes were not closely related to changes in yield.Soil salinity increased with increasing salinity of the applied water. However, during the irrigation season water penetration and the accumulation of salt within the profile was predominantly restricted to the 0–60 cm depth. No portion of the applied irrigation water was available as a leaching fraction. Any leaching of salts to the watertable, particularly below 120 cm, was due to winter rainfall rather than the application of summer irrigation water.Ripping the soil to a depth of 75 cm increased water infiltration and resulted in increased crop yields, but did not significantly affect the crop relative yield-soil ECe relationship.From the results it is proposed that on the slowly permeable duplex soils, when watertable depth is controlled, management strategies for lucerne irrigated with saline water should be based on controlling the salinity of the shallow soil depths, to 60 cm.