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.     

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.     

Effect of saline irrigation on germination and growth parameters of barley (Hordeum vulgare L.) in a pot experiment

The effect of saline irrigation was investigated on germination and growth parameters of six barley (Hordeum vulgare L.) cultivars in a pot experiment. The crop germination decreased between 24–35% with irrigation water having EC of 9.26 dS m⁻¹, 28–47% with water EC of 13.4 dS m⁻¹ and 30–53% with water EC of 16.28 dS m⁻¹ among various cultivars. The sequence of reduction in germination was Hassawi > Gusto > Madini > M. Khariji > Qassimi. Plant height and total number of plant tillers decreased significantly with increasing irrigation-water salinity. Plant height ranged between 39.43 cm (Qassimi cultivar) with water EC of 3.00 dS m⁻¹ to 1.97 cm (Gusto) with water EC of 16.28 dS m⁻¹ whereas the range for total number of plant tillers per pot was 77.00 (Qassimi) with irrigation EC of 3.00 dS m⁻¹ to 9.67 (Gusto) with irrigation EC of 16.28 dS m⁻¹. The trend of reduction in plant height for different cultivars was Gusto > Qassimi > Hassawi > Madini > M. Khariji whereas for plant tillers, the sequence was Gusto < Hassawi < M. Khariji < Qassimi < Madini. Greenmatter and drymatter yield decreased significantly with increasing irrigation water salinity. The greenmatter yield ranged between 138.67 g per pot (Madini) with water EC of 3.00 dS m⁻¹ to 11.40 g per pot (Gusto) with water EC of 16.28 dS m⁻¹. A similar trend was found for drymatter yield. The trend of reduction in yield among various cultivars (both greenmatter and drymatter) was Gusto > Hassawi > M. Khariji > Qassimi > Madini. Overall sequence of salt tolerance for different barley cultivars was Madini > Qassimi > M. Khariji > Hassawi > Gusto. A comparison of cultivars indicated that irrigation waters with EC 13.40 dS m⁻¹ and above reduced crop germination and greenmatter production to a significant level. In conclusion, there exists a lot of potential for a reasonable production of barley as forage crop with irrigation water having salinity up to 9.26 dS m⁻¹ provided 15% extra water above crop-water requirement is applied as leaching requirements to control soil salinity.     

Response of tall fescue to irrigation water salinity,leaching fraction,and irrigation frequency

A long-term study in the rhizotron at the U.S. Salinity Laboratory established the yield and evapotranspiration of tall fescue as a function of irrigation water salinity, leaching fraction, and irrigation frequency. As the salt concentration of the irrigation water increased or leaching fraction decreased, dry matter production was reduced significantly. Differences in production because of irrigation frequency, however, were insignificant. With low stress (high leaching, L = 0.27, and low salinity water, S = 1 dS/m) annual dry matter yields were 2.0 kg/m², compared to annual yields of 1.4 kg/m² with high stress (low leaching, L = 0.09, and high salinity water, S = 4 dS/m).Annual evapotranspiration dropped from 1860 mm for low stress treatments to 1170 mm for high stress. Soil evaporation was negligible for the mature grass stand. In concurrence with several models, relative dry matter production was proportional to relative water use.The salt tolerance of treatments dominated by osmotic potential was in agreement with that published for tall fescue. As matric potential decreased among treatments yields fell significantly below that predicted by the salt tolerance model.     

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)     

Nitrogen fixation in a white clover-grass pasture irrigated with saline groundwater

Nitrogen (N₂) fixation in an irrigated white clover-grass sward was estimated using the ¹⁵N isotope dilution technique following the addition of K¹⁵NO₃ at 0.5 gN m^–2 and 80 atom % ¹⁵N in a field study during the 1990–91 season. Two water salinity treatments (channel water; EC_w = 0.07 and groundwater; 2.4 dS m^–1) and four irrigation frequencies were included in a factorial design with four replicates. The channel water treatments were irrigated when pan evaporation minus rainfall equalled 50 mm, whereas the groundwater treatments were irrigated at deficits of 40, 50, 65 or 80 mm. Cumulative dry matter of the clover was significantly less in treatments irrigated with saline groundwater compared to channel water at day 164, and soil salinities (EC_e) increased on average from 2.3 to 5.07 dS m^–1. In contrast, salinity of the irrigation water had no effect on the cumulative yield of grass. Cumulative dry matter of the grass and clover were not affected by groundwater irrigation frequency. Total N accumulation by the grass did not differ significantly between treatments. However, total N accumulation in white clover was significantly less (P < 0.05) in all treatments irrigated with groundwater compared to channel water. Neither the N concentrations of the grass nor the clover differed significantly between the salinity treatments. Salinity and irrigation frequency had no effect on the proportion of clover N (P_atm) derived from N₂ fixation. The values of P_atm were high throughout, and increased progressively from 0.78 at day 39 to 0.91 at day 164 (P < 0.01). However, the yield of fixed N was lower in clover when watered with groundwater compared to channel water (P < 0.01). Thus low to moderate soil salinity did not affect the symbiotic dependence of clover, but the yield of biologically-fixed N was depressed through a reduction in the dry matter yield of the legume.     

Uptake of shallow groundwater by cotton: growth stage,groundwater salinity effects in column lysimeters

A 3-year column lysimeter experiment was conducted with cotton (Gossypium hirsutum L.) to determine the influence of shallow groundwater salinity on groundwater uptake. Nonsaline (0.3 dS m⁻¹) irrigation water was applied at 7-day intervals throughout the growing season, with the cotton allowed to use stored soil water and groundwater as root water uptake permitted. Groundwater salinities ranging from 0.3 dS m⁻¹ electrical conductivity (EC_w) to 30.8 dS m⁻¹ were evaluated. Water for leaching was applied following harvest each year in amounts adequate to produce a nonsaline soil profile at the beginning of each year. Equations were developed to describe relationships between day of year, growth stage or growing degree days and shallow groundwater uptake. Groundwater contributed about 30 to 42% of seasonal total evapotranspiration (ET) in treatments with groundwater salinity ≤ 20 dS m⁻¹ but declined to 12 to 19% of total ET at higher salinity levels.     

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

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/m²).     

Water-use efficiency of irrigated winter maize under cool weather conditions of India

Field experiments were conducted during 1993/94 and 1994/95 in the sub-humid tropic environment of northern India to identify suitable irrigation schedule(s) for winter maize (December to May). Based on plant growth stages, viz. knee-high, tasselling, flowering, silking, grain-filling and dough, which occurred, respectively, at 55, 75, 95, 105, 125 and 145 days after planting, the crop was subjected to six irrigation treatments, which were: no irrigation (I₀); irrigation given at all the growth stages (I₁); irrigation missed at knee-high (I₂); at knee-high and dough (I₃); at knee-high, flowering and grain-filling (I₄); and at knee-high, flowering, silking and dough stages (I₅). The change in profile soil water content, (W (depletion) of the entire crop-growing season was found to be in the order I₀ >I₅ >I₄ >I₃ >I₂ >I₁. Of the total net water use (NWU), about 87% was evapotranspiration and 13% deep percolation losses. The NWU was highest (472 and 431 mm) under I₁ and lowest (223 and 240 mm) under the I₀ treatment during the two cropping seasons. Compared to I₁, NWU in I₃ decreased by 23% and 12.3% and in I₄ by 33.8% and 24.2% in the two cropping seasons. However, there was no statistically significant difference (at LSD, P=0.05) between yields of the I₁ to I₄ treatments during either year. The NWU was found to be in the order I₁ >I₂ >I₃ >I₄ >I₅ >I₀, whereas the water-use efficiency (WUE) based on NWU was found to be in the reverse order: I₅ >I₄ >I₃ >I₀ >I₂ >I₁. Maximum yield (5.14 t ha^-1) with WUE of 1.39 kg m^-3 was obtained under the I₃ treatment. However, optimum yield (4.91 t ha^-1) with high WUE of 1.54 kg m^-3 was under I₄. Accordingly, irrigation applications greater than 240 mm did not provide additional yield of winter maize. Frequent irrigations (I₁) proved detrimental to grain yield of winter maize in the northern Indian plains, especially under cool weather conditions, where minimum temperature (6°C) can be accompanied by occasional frost.     

Trickle irrigation of cotton: Effect on soil chemical properties

The management of soil salinity and sodicity in the root zone (0–150 cm) of Panoche clay loam soil was studied during three consecutive growing seasons in a field experiment designed to determine the water requirement of Acala SJ-2 cotton (Gossypium hirsutum L.) under trickle irrigation in the western San Joaquin Valley of California. The trickle irrigation treatments (20, 40, 60, 80 and 100% of the previous day's pan evaporation, PE) were imposed on each of three preplant furrow irrigation depths of 0, 190 and 380 mm. The electrical conductivity, EC, of the irrigation water ranged from 0.4 to 0.5 dS m⁻¹ unless groundwater had to be mixed with the surface supply; this practice raised the EC to 0.6–0.9 dS m⁻¹ for short time periods. The unadjusted sodium adsorption ratio, SAR, of the irrigation water averaged < 4.Soil salinity, as measured by EC_e, was < 5 dS m⁻¹ and sodicity, as measured by SAR_e, was < 15 in the root zone. Changes in these soil chemical properties were more related to the amount of preplant irrigation at the lower (< 40% PE) trickle-irrigation levels than at the higher levels. Results suggest that soil salinity and sodicity can be maintained at acceptably low levels by appropriate preplant irrigation with consideration to amount of winter rainfall; even when during the season only sufficient trickle irrigation is given to meet crop water requirements without regards to leaching needs. The lint cotton yields over the 3-year period ranged from 357 to 1542 kg ha⁻¹; the corresponding applied water ranged from 175 to 744 mm.     

Soil salinity reduction and prediction of salt dynamics in the coastal ricelands of Bangladesh

Field experiments were conducted in moderately saline and saline soils during the 1996 dry and wet seasons and the 1997 dry season to document salt dynamics and establish their relationship with local hydrology. Topsoil (0–15 cm) salinity in the dry season varied from 4.0 to 9.0 dS m⁻¹ in moderately saline soils at Mirzapur and from 5.0 to 12.0 dS m⁻¹ in saline soils at Barodanga. In wet season, the corresponding figures were from 1.5 to 2.5 dS m⁻¹ and from 2.0 to 3.0 dS m⁻¹, respectively. Dry season cropping significantly reduced topsoil salinity at both the research sites. Overall peak salinity in non-plowed cropped lands was 25–38% lower than that of fallow lands, and in plowed cropped lands it was about 30–40% less than the non-plowed cropped lands.Multiple linear and non-linear regression models were developed to predict topsoil salinity of the fallow land for both moderately saline and saline soils by using daily rainfall and evaporation as independent variables. The prediction level was not significantly improved when a non-linear model was employed in place of linear model. Therefore, a linear model may be used to predict topsoil salinity of the coastal ricelands of Bangladesh.     

Response of alfalfa (<Emphasis Type="Italic">Medicago sativa</Emphasis> L.) to diurnal and nocturnal saline sprinkler irrigations. I: total dry matter and hay quality

Little information is available on the quantitative effects on crops of saline sprinkler irrigations and the presumable beneficial effects of nocturnal versus diurnal irrigations. We measured crude protein content, carbon isotope discrimination and total dry matter (TDM) of alfalfa (Medicago sativa L.) subject to diurnal and nocturnal saline sprinkler irrigations. The work was carried out in Zaragoza (Spain) during the 2004–2006 growing seasons with a triple line source sprinkler system using synthetic saline waters dominated by NaCl with an irrigation water EC ranging from 0.5 to 5.6 dS m⁻¹. The quality of alfalfa hay assessed through its crude protein concentration was not significantly affected by salinity. Carbon isotope discrimination, an indicator of the effect of osmotic stress on plant water status, tended to decrease with increases in salinity. Based on a piecewise linear response model, alfalfa grown under saline sprinkler irrigation was shown to be more tolerant (threshold soil salinity, EC_e = 3.5 dS m⁻¹) than in previous experiments under surface irrigation (threshold EC_e = 2.0 dS m⁻¹) at relatively low salinity values, but became more sensitive at higher salinity values as shown by the higher absolute slope (13.4%) for sprinkler as compared to surface irrigation (7.3%). No significant differences in TDM were found between diurnal and nocturnal saline sprinkler irrigations. The recommended practice of irrigating at night for sprinkler irrigation using saline water is therefore not supported by our results in alfalfa grown under semiarid conditions.     

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.     

Distribution and dynamics of soil water and salt under different drip irrigation regimes in northwest China

A 2-year experiment was carried out to investigate the effects of different drip irrigation regimes on distribution and dynamics of soil water and salt in north Xinjiang, China. Five treatments—F7 (0.24 dS m^?1 + Once every 7 days), B7 (4.68 dS m^?1 + Once every 7 days), S7 (7.42 dS m^?1 + Once every 7 days), F10 (0.24 dS m^?1 + Once every 10 days) and F3 (0.24 dS m^?1 + Once every 3 days)—were designed. For all treatments, additional 150-mm fresh water was applied on 10th November in 2009 (winter irrigation) to leach the accumulated salt. The results revealed that irrigation frequency and water quality had significant effects on the spatial distribution and change of soil water content, soil salt and the crop water consumption rate, but had a limited impact on the seasonal accumulative water consumption, and the cotton yield decreased with the decrease in irrigation frequency and water quality on the whole. During the cotton growing season, results showed that the salt mainly accumulated in the 0- to 60-cm soil layer, while the soil salt in 60- to 100-cm layer changed slightly, indicating that the drip irrigation could not leach the soil salt out of the root zone under the irrigation regimes. Therefore, salt leaching was necessary to maintain the soil water–salt balance and to prevent excessive salt accumulation in the root zone. After the 150-mm winter irrigation and subsequent thawing, soil salts were leached into the deeper layers (below 60 cm), and the soil salt content (SSC) (EC_1:5) in root zone in the next year was about 0.2 dS m^?1. Moreover, compared to 2009 season, the SSC within the root zone did not increase even the EC of the irrigation water was up to 7.42 dS m^?1. Additionally, it is important to note that the results were concluded based on the data of the 2-year experiment; further studies are need to optimize winter irrigation amount and assess the sustainability of saline water irrigation since long-term utilization of saline water may lead to soil degradation.     

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.     

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.     

Shoot growth and fruit development of muskmelon under saline and non-saline soil water deficit

In irrigated agriculture, the production of biomass and marketable yield depend largely on the quantity and salinity of the irrigation water. The sensitivity of field-grown muskmelon (Cucumis melo L. cv. Galia) to water deficit was compared, using non-saline (EC_i= 1.2 dS m^–1) and saline (EC_i=6.3 dS m^–1) water. Drip irrigation was applied at 2-day intervals at seven different water application rates for each water quality, including a late water-stress treatment. Neutron scattering measurements showed that the soil layers below the root zone remained dry throughout the experiment, indicating negligible deep percolation. Thus, the sum of the seasonal amount of applied water and the change in soil moisture approximated the cumulative evapotranspiration (ET). Gradual buildup of water and salt stresses resulted in small treatment effects on the size of the vegetative cover and large effects on leaf deterioration and fruit production. Crop responses to salinity may result from an osmotic component of the soil water potential or from other salt effects on the crop physiology. Relating plant data to cumulative ET allowed a distinction to be made between the effect on water availability and specific salinity effects. The relation between fruit fresh weight and ET was not sensitive to EC_i. The slopes for fruit dry weights were also insensitive to EC_i but the intercept was larger for saline treatments. At any given ET saline water increased fruit number, increased fruit dry matter content and decreased fruit netting, in comparison with non-saline water. The combination of salinity and soil-water deficit was detrimental to fruit quality. Saline soil-water deficit decreased the percentage of marketable (netted) fruit and caused an early end to the period of marketable fruit production. Non-saline soil-water deficit increased the percentage of marketable fruit and had no effect on the duration of the production period. Late non-saline water stress caused a pronounced increase in the percentage of marketable fruit.     

Effect of irrigation methods,management and salinity of irrigation water on tomato yield,soil moisture and salinity distribution

The increasing demand for irrigation water to secure food for growing populations with limited water supply suggests re-thinking the use of non-conventional water resources. The latter includes saline drainage water, brackish groundwater and treated waste water. The effects of using saline drainage water (electrical conductivity of 4.2–4.8 dS m⁻¹) to irrigate field-grown tomato (Lycopersicon esculentum Mill cv Floradade) using drip and furrow irrigation systems were evaluated, together with the distribution of soil moisture and salt. The saline water was either diluted to different salinity levels using fresh water (blended) or used cyclically with fresh water. The results of two seasons of study (2001 and 2002) showed that increasing salinity resulted in decreased leaf area index, plant dry weight, fruit total yield and individual fruit weight. In all cases, the growth parameters and yield as well as the water use efficiency were greater for drip irrigated tomato plants than furrow-irrigated plants. However, furrow irrigation produced higher individual fruit weight. The electrical conductivity of the soil solution (extracted 48 h after irrigation) showed greater fluctuations when cyclic water management was used compared to those plots irrigated with blended water. In both drip and furrow irrigation, measurements of soil moisture one day after irrigation, showed that soil moisture was higher at the top 20 cm layer and at the location of the irrigation water source; soil moisture was at a minimum in the root zone (20–40 cm layer), but showed a gradual increase at 40–60 and 60–90 cm and was stable at 90–120 cm depth. Soil water content decreased gradually as the distance from the irrigation water source increased. In addition, a few days after irrigation, the soil moisture content decreased, but the deficit was most pronounced in the surface layer. Soil salinity at the irrigation source was lower at a depth of 15 cm (surface layer) than that at 30 and 60 cm, and was minimal in deeper layers (i.e. 90 cm). Salinity increased as the distance from the irrigation source increased particularly in the surface layer. The results indicated that the salinity followed the water front. We concluded that the careful and efficient management of irrigation with saline water can leave the groundwater salinity levels unaffected and recommended the use of drip irrigation as the fruit yield per unit of water used was on average one-third higher than when using furrow irrigation.     

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).     

Response of alfalfa (<Emphasis Type="Italic">Medicago sativa</Emphasis> L.) to diurnal and nocturnal saline sprinkler irrigations. II: shoot ion content and yield relationships

When using saline waters, sprinkling irrigation at night is a recommended practice to reduce evaporation, salt absorption by the wetted leaves and its negative effects on crops. We measured shoot ion concentrations (Cl⁻, Na⁺ and K⁺) and total dry matter (TDM) in alfalfa subject to diurnal and nocturnal saline sprinkler irrigations and established potential relationships among them. The work was carried out along the 2004–2006 growing seasons using EC waters from 0.5 to 5.6 dS m⁻¹. Saline sprinkling irrigations linearly increased shoot Cl⁻ and Na⁺ and decreased shoot K⁺. Even though daytime evaporation was much higher than nigh-time, shoot ion accumulation and TDM were similar in the diurnal and nocturnal irrigations. The salinity tolerance of alfalfa decreased in year 2006 due to increases in shoot Cl⁻ and, particularly, shoot Na⁺. The lower threshold for shoot Na⁺ (276 meq kg⁻¹) than for shoot Cl⁻ (726 meq kg⁻¹) shows that alfalfa is more sensitive to Na⁺ than to Cl⁻, and that Na⁺ accumulation is the preponderant cause of alfalfa yield decline after 3 years of sprinkling with saline waters.