A model for assessing crop response to salinity

CropSyst, a management-oriented crop growth model, was modified to assess crop response to salinity. The effect of salinity was included in the existing water uptake module by adding an osmotic component to the soil water potential and developing a function to account for salinity effects on root permeability. The effect of salinity on water uptake is the link to simulate crop growth reduction. A qualitative analysis showed that the model simulated expected trends of crop response to salinity as affected by cultivar tolerance, atmospheric vapor pressure deficit, and soil water availability. Comparisons with data from sprinkler line experiments were performed for barley grown at Zaragoza (Spain) in 1986 and 1989, and corn at Davis, Calif. and Fort Collins, Colo. in 1975. These experiments included different salinity and irrigation levels. At Davis, the model simulated well the effect of salinity/irrigation treatments on water use, biomass, and crop yield, with values for the Willmot index of agreement (d) generally better than 0.94 (a value of 1.0 implying perfect agreement). At Fort Collins, simulation of grain yield was less satisfactory (d fluctuated between 0.83 and 0.90), but the agreement was good for crop water use and biomass (d generally better than 0.96). The lower performance for grain yield was attributed to large and erratic variations in the observed harvest index. The agreement between simulated and observed values tended to be lower at Zaragoza, with d values fluctuating between 0.84 and 0.91 for biomass and yield in the 2 years included in this evaluation. Unusually high measured yields in 1989 and erratic variation in 1986 were attributed to small sample size. The small size (increased measurement error) of samples typically obtained in sprinkler line source experiments tends to limit their use for evaluation of simulation models.     

DRAINMOD-S: Water management model for irrigated arid lands,crop yield and applications

The primary objective of an agriculture water management system is to provide crop needs to sustain high yields. Another objective of equal or greater importance in some regions is to reduce agriculture impacts on surface and groundwater quality. Kandil et al. (1992) modified the water management model DRAINMOD to predict soil salinity as affected by irrigation water quality and drainage system design. The objectives of this study are to incorporate an algorithm to quantify the effects of stresses due to soil salinity on crop yields and to demonstrate the applications of the model. DRAINMOD-S, is capable of predicting the long-term effects of different irrigation and drainage practices on crop yields. The overall crop function in the model includes the effects of stresses caused by excessive soil water conditions (waterlogging), soil water-deficits, salinity, and planting delays. Three irrigation strategies and six drain spacings were considered for all crops. In the first irrigation strategy, the irrigation amounts were equal to evapotranspiration requirements by the crops, with the addition of a 10 cm depth of water for leaching applied during each growing season. In the second strategy, the leaching depth (10 cm) was applied before the growing season. In the third strategy, a leaching depth of 15 cm was applied before the growing season for each crop. Another strategy (4th) with more leaching was considered for bean which is the crop most sensitive to salinity. In the fourth strategy, 14 days intervals were used instead of 7 and leaching irrigations were applied: 15 cm before the growing season and 10 cm at the middle of the growing season for bean. The objective function for these simulations was crop yield. Soil water conditions and soil salinity were continuously simulated for a crop rotation of bean, cotton, maize, soybean, and wheat over a 19 years period. Yields of individual crops were predicted for each growing season. Results showed that the third irrigation strategy resulted in the highest yields for cotton, maize, soybean and wheat. Highest yields for bean were obtained by the fourth irrigation strategy. Results are also presented on the effects of drain depth and spacing on yields. DRAINMOD-S is written in Fortran and requires a PC with math-coprocessor. It was concluded that DRAINMOD-S is a useful tool for design and evaluation of irrigation and drainage systems in irrigated arid lands.     

Influence of different water quantities and qualities on lemon trees and soil salt distribution at the Jordan Valley

The influences of water quantity and quality on young lemon trees (Eureka) were studied at the University of Jordan Research Station at the Jordan Valley for 5 years (1996–2000). Five water levels and three water qualities were imposed via trickle irrigation system on clay loam soil. The primary effect of excess salinity is that it renders less water available to plants although some is still present in the root zone. Lemon trees water requirements should be modified year by year since planting according to the percentage shaded area, and this will lead into substantial water saving. Both evaporation from class A pan and the percentage shaded area can be used to give a satisfactory estimate of the lemon trees water requirement at the different growth stages. The highest lemon fruit yield was at irrigation water depth equal to evaporation depth from class A pan when corrected for tree canopy percentage area. Increasing irrigation water salinity 3.7 times increased average crop root zone salinity by about 3.8–4.1 times.The high salt concentration at the soil surface is due to high evaporation rate from wetted areas and the nature of soil water distribution associated with drip irrigation system. Then, the salt concentration decreased until the second depth, thereafter, salt concentration followed the bulb shape of the wetted soil volume under trickle irrigation. Irrigation water salinity is very important factor that should be managed with limited (deficit) irrigation. But increasing amount of applied saline water could result in a negative effect on crop yield and environment such as increasing average crop root zone salinity, nutrient leaching, water logging, increasing the drainage water load of salinity which might pollute ground water and other water sources.     

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)     

Deficit irrigation under water stress and salinity conditions: The MOPECO-Salt Model

In both arid and semi-arid areas the use of saline water for irrigation is a common practice, even though it may cause a drop in crop yield and progressive soil salinization. In order to determine the most suitable irrigation strategy for higher yield, profitability, and soil salinity management of certain crops, the MOPECO-Salt Model has been developed. This model was first validated in the Eastern Mancha Agricultural System in Albacete (Spain) through a test carried out on onion crop in April-September 2009, where the simulated yield was 2% lower than the observed one. The model was then tested at Tal Amara Research Station in the Central Bekaa Valley Agricultural System (Lebanon) using data from a 5-year experiment on the effects of deficit irrigation on two cultivars of potato (Spunta: July-October 2001, and June-September 2002; and Agria: March-August 2004, 2005, and 2007). Furthermore, these results were compared with those obtained through AquaCrop, which does not currently assess crop response to salinity. Differences between observed and simulated yields were lower than 3% for MOPECO-Salt and up to 12% for AquaCrop. According to findings from simulations, the irrigation strategies without leaching fraction employed in both areas are remediable since the off-season rainfall is sufficient to wash out soluble salts supplied with irrigation water. Results showed that as much as 14.4% water could be saved when this strategy was adopted for onion crops.     

Drip Irrigation of Tomato and Cotton Under Shallow Saline Ground Water Conditions

Artificial subsurface drainage is not an option for addressing the saline, shallow ground water conditions along the west side of the San Joaquin Valley because of the lack of drainage water disposal facilities. Thus, the salinity/drainage problem of the valley must be addressed through improved irrigation practices. One option is to use drip irrigation in the salt affected soil.A study evaluated the response of processing tomato and cotton to drip irrigation under shallow, saline ground water at depths less than 1 m. A randomized block experiment with four irrigation treatments of different water applications was used for both crops. Measurements included crop yield and quality, soil salinity, soil water content, soil water potential, and canopy coverage. Results showed drip irrigation of processing tomato to be highly profitable under these conditions due to the yield obtained for the highest water application. Water applications for drip-irrigated tomato should be about equal to seasonal crop evapotranspiration because yield decreased as applied water decreased. No yield response of cotton to applied water occurred indicating that as applied water decreased, cotton uptake of the shallow ground water increased. While a water balance showed no field-wide leaching, salinity data clearly showed salt leaching around the drip lines.     

Cyclic and blending strategies for using nonsaline and saline waters for irrigation

Summary Large quantities of saline water frequently exist in irrigated areas of the world. Various strategies have been proposed to use these saline waters. Blending involves mixing saline water with good quality water to an acceptable salinity and then using this water to irrigate crops. The cyclic strategy uses waters of various salinities separately either during one season or in a crop rotation as a function of the crop's salt tolerance. A multi-seasonal transient state model, known as the modified van Genuchten-Hanks model, was used to investigate the effects of cyclic or blending application of irrigation waters of two salinity levels on alfalfa (Medicago sativa L.), and on a corn (Zea mays L.) and cotton (Gossypium hirsutum L.) crop rotation. Simulated alfalfa yields were similar for the cyclic and blending strategies that applied the same amount of salt and water. The cyclic strategy produced higher simulated yields of salt-sensitive corn than the blending strategy, whereas the simulated salt-tolerant cotton yield was not affected by the two strategies. The beneficial effects of the cyclic strategy on corn production decreased under deficit irrigation.     

Assessment and management of poor quality waters for crop production: A simulation model (SWAM)

A simulation model has been prepared for assessing water quality to judge its suitability for irrigation. When water is classified as poor quality water (saline/sodic/saline-sodic) utilizing standard norms for Indian agro-climatic conditions, the model determines the potential of the water for direct application. Further, it also evaluates management strategies based on conjunctive use of fresh and saline waters. For this purpose, the model requires water quality data, crop data, soil data and rules established in the expert system rule-base. Data are compiled in data files which can be updated. For conjunctive use of saline and fresh waters, an irrigation scheduling sub-model has been modified to include a soil salinization-desalinization module based on layer-wise equilibrium theory. The module was independently tested using field data. The model SWAM has been successfully tested using data from a number of field experiments. Sodic waters of 16.2 meq l⁻¹ residual sodium carbonate would require 2.73 t ha⁻¹ of gypsum for each 20 cm of water applied to the soil. Field observations usually attest to this requirement. Likewise, saline water of 16 dS m⁻¹, when applied to a wheat crop in conjunction with fresh water of 0.5 dS m⁻¹, would yield optimally in case two saline water irrigations are followed by one fresh water irrigation in a normal rainfall year with an initial soil salinity of 2.98 dS m⁻¹. Some more useful data sets are analyzed and compared with results from field experiments. In our opinion, the model which is based upon recent guidelines can be applied to the classification of waters and their management. The minor changes necessary to apply the model to other conditions can be easily carried out.     

Crop coefficients for irrigating cotton in the presence of groundwater

A cotton crop coefficient was modified to account for the contribution of shallow groundwater to crop water use. The data used in the modification were developed using weighing column lysimeters. The percentage groundwater contribution to crop water use, expressed as a function of growing degree days for several salinities and two water table depths, was used in the regression analysis. Use of the modified coefficient was demonstrated by scheduling a subsurface drip irrigation system installed in an area with shallow saline groundwater. Use of the modified crop coefficient resulted in 25% of the cotton water requirement being extracted from shallow groundwater with a salinity of 5 dS m^-1 without any adverse effects on vegetative plant growth and yield. Groundwater depth dropped from 1.2 to 2.2 m during the growing season.     

Effect of irrigation water salinity on transpiration and on leaching requirements: A case study for bell peppers

Maximization of crop yields when the salinity of irrigation water is high depends on providing plant transpiration needs and evaporative losses, as well as on maintaining minimum soil solution salinity through leaching. The effect of the amount of applied irrigation water was studied regarding transpiration, yields, and leaching fractions as a function of irrigation water salinity. Bell pepper (Capsicum annum L. vars. Celica and 7187) in protected growing environments in the Arava Valley of Israel was used as a case study crop to analyze water quantity–salinity interactions in a series of lysimeter, field and model simulation experiments. Leaching fraction was found to be highly influenced by plant feedback, as transpiration depended on root zone salinity. Increased application of saline irrigation water led to increased transpiration and yields. The higher the salinity level, the greater the relative benefit from increased leaching. The extent of leaching needed to maximize yields when irrigating with saline water may make such practice highly unsustainable.     

Simulation of the dry matter production and seed yield of common beans under varying soil water and salinity conditions

We present a model that simulates the effects of water and salinity stress on the growth of beans. The model derives a combined soil water/salinity stress factor from the total water potential (combination of the matric and the osmotic potentials) and uses this stress factor as a growth limiter in a growth model. The model was tested on data obtained from two greenhouse trials of beans (Phaseolus vulgaris) grown under a range of soil water and salinity conditions. The simulated dry weight of the bean generally followed those observed. In the first trial, the comparison between simulated and observed total dry weight and seed yield gave R² values of 0.97 and 0.92, respectively. Comparison of the simulated to the observed dry weight for the second trial gave R² values of 0.85 and 0.89, respectively. These indicate a good performance of the model in general. The principle of deriving a combined water/salinity stress from the matric and osmotic potentials is simple and can be included as a simple routine in many existing crop models without much difficulty.     

Effect of sustained saline irrigation on soil salinity and crop yields

Summary Field studies were conducted for a period of ten years (1974 to 1984) on Typic Ustochrept to determine the sustained effects of saline irrigation water electrical conductivity (EC _iw ) 3.2 dS/m, sodium adsorption ratio (SAR) 21 (mmol/1)^1/2 and residual sodium carbonate (RSC) 4me/1, on the build up of salinity in the soil profile and yield of crops grown under fixed rice-wheat and maize/millet-wheat rotations. Saline waters were continuously used with and without the addition of gypsum (at the rate needed to reduce RSC to zero) applied at each irrigation. In maize/millet-wheat rotation, two additional treatments viz. (i) irrigation with 50% extra water over and above the normal 6 cm irrigation, and (ii) irrigation with good water and saline water alternately, were also kept. The results showed that salinity increased rapidly in the profile during the initial years but after five years (1979–1984) the average soluble salt concentration in 0–90 cm soil profile did not appreciably vary and the mean EC _e values under saline water treatment remained almost similar to EC _iw , under both the crop rotations.Saline water irrigation increased pH and Na saturation of the soil, reduced water infiltration rate and decreased yields of maize, rice and wheat. The differences in the build up of salinity and ESP of the soil under the two cropping sequences seemed to be related with the differences in leaching that occurred under rice-wheat and maize/millet-wheat rotations. Application of gypsum increased the removal of Na from the profile, appreciably decreased the pH and Na saturation and improved water infiltration rate and raised crop yields. Application of non-saline and saline waters alternately was found to be a useful practice but irrigation with 50% extra water to meet the leaching requirement did not control salinity and hence lowered crop yields.     

Effect of saline water irrigation and manure application on the available water content, soil salinity, and growth of wheat

Good water management combined with appropriate soil management is necessary for sustainable crop production in drylands. A pot culture experiment was conducted using sand dune soil under greenhouse conditions to evaluate the response of wheat (Triticum aestivum L.) to the application of farmyard manure (FYM) or poultry manure (PM), and irrigation with water at two salinity levels (0.11 and 2.0 dS m⁻¹) and two irrigation intervals (daily and every second day). The manure was applied at a rate of 20 Mg ha⁻¹. The soil water content, measured 1 h before every irrigation, showed that soil treated with PM retained more water than that treated with FYM, while the control (no manure) contained the least water. FYM treatment resulted in 78 and 21% higher dry matter yield compared to the control and PM treatments, respectively, under daily irrigation using good-quality water. The increase was 29 and 55%, respectively, when saline water was used for daily irrigation. A similar trend was observed with the alternate day irrigation treatment; FYM gave the highest dry matter yield. The number of tillers and plant height showed that FYM was better than PM, which in turn was better than the control under irrigation with good-quality water regardless of the irrigation interval. When water of the highest salinity was used for irrigation, FYM was still always the best, but the control was now better than the PM treatment. The electrical conductivity of the soil measured at the end of the experiment was slightly higher with PM, as compared to the FYM and control treatments. A significant interaction between irrigation water quality and manure application was observed, affecting plant growth. PM aggravated the adverse affect of saline water on plant growth by increasing soil salinity.     

Irrigation management methods for reducing water use of cowpea (Vigna unguiculata [L.] Walp.) and lima bean (Phaseolus lunatus L.) while maintaining seed yield at maximum levels

Summary In a previous study conducted at the University of California at Riverside, it was shown that water use of cowpea could be reduced while maintaining seed yields by withholding irrigation during the vegetative stage in a rain-free environment, and then irrigating when estimates based on potential evapotranspiration, indicated 40% depletion of available moisture in 90-cm depth of soil. The general applicability of this efficient irrigation management method was tested by experiments conducted at the West Side Field Station in the San Joaquin Valley of California with six irrigation treatments, three different row spacings (single rows on 76- and 102-cm beds, and double rows on a 102-cm bed), a semi-erect cultivar of cowpea (Vigna unguiculata [L.] Walp.), and a prostrate cultivar of lima bean (Phaseolus lunatus L.).Withholding irrigation during the vegetative stage following pre-irrigation substantially reduced dry matter at anthesis (–17% to –38%) and water use (–101 mm) of cowpea, but did not influence seed yield or shoot dry matter at harvest for either cowpea or lima bean. Increasing the irrigation interval until 75% nominal depletion of available water in 90-cm depth of soil reduced water use (–139 cm), but did not affect seed yield of cowpea. Lima bean, however, showed a significant decrease in shoot dry matter production (–17%) and in seed production (–18%) at the longest irrigation interval involving 75% nominal depletion. The different row spacings used in this experiment did not affect shoot dry matter or seed production of the semi-erect cowpea. However, shoot dry matter and seed yield were significantly greater for the prostrate lima bean grown with double rows on a 102-cm bed. Seed yield was 46% and 18% greater than with single rows on 76-cm and 102-cm beds, respectively. Generally, variations in seed yields of lima bean were positively correlated with variations in shoot dry matter production.Nominal depletion of available soil water provided a practical method for scheduling irrigations, but the results with cowpea indicated that the critical level, which resulted in the greatest reductions in water use while maintaining maximum seed yield varied from 40% (at Riverside) to 75% (at West Side Field Station). Additional methods are needed to fine-tune irrigation which is based mainly on nominal depletion of available water. Generally, pressure chamber estimates of leaf water potential exhibited too little variation among plants subjected to different irrigation treatments for it to be useful for fine-tuning irrigation schedules for either cowpea or lima bean. However, differences in temperature between canopy and air, when expressed as a function of either vapor pressure deficit or canopy temperature, and related to percent reduction in yield, appeared to have sufficient resolution to provide a practical method for fine-tuning irrigation schedules for cowpea during flowering and pod-filling, but not lima bean. Normalizing temperature differences with vapor pressure deficit was more effective, but normalizing with canopy temperatures is more convenient because it does not require a measurement of air humidity.     

内蒙古河套灌区咸水灌溉的环境效应分析

研究了咸水灌溉对土壤水盐动态、地下水位、地下水质、作物生长及产量的影响。灌溉水源为黄河水和高矿化度地下水混合。咸水灌溉期间,土壤盐分有所增加,通过控制咸水灌溉定额,以及进行合理的黄河水秋浇灌溉,可以达到年度内土壤盐分动态平衡。咸水灌溉条件下,作物长势及产量基本不受影响。适宜合理的咸水灌溉不会造成环境恶化,而且对缓解河套灌区水资源紧张的矛盾有着重要意义。     

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.     

Water use efficiency of narrow row cotton

Summary A field experiment was conducted on the west side of the San Joaquin Valley in California to determine water use, crop growth, yield and water use efficiency of Acala (SJ-2) cotton (Gossypium hirsutum L.) grown in 0.5 m spaced rows on a Panoche clay loam soil (Typic Torriorthents). Evapotranspiration was determined by water balance techniques utilizing neutron soil moisture measurements. All neutron measurements were made within a 3 m soil profile in 0.20 m increments. The measured evapotranspiration was compared to climatic estimates of potential evapotranspiration, and to calculations using a one-dimensional soil water balance model that separately computed soil water evaporation and plant transpiration. Crop growth was determined by weekly destructive plant sampling. Leaf area was determined along with dry matter components of leaves, stems, fruiting parts (flowers and squares) and bolls. Final yield was determined by machine harvesting (brush stripper) 720 m² from each plot. Lint yields and fiber quality were determined by sample ginning and fiber analysis at the U.S. Cotton Research Station at Shafter, California. Three irrigation regimes were established that resulted in an evapotranspiration range from a high deficit condition to full irrigation at the calculated atmospheric demand.The measured evapotranspiration of narrow row cotton under a full irrigation regime was 778 mm, 594 mm under a limited irrigation regime and 441 mm under a regime with no post-plant irrigation. The evapotranspiration from these irrigation treatments was accurately simulated by a water balance model. that used inputs of potential evapotranspiration, leaf area index, soil water holding capacity and root development.The average lint yield from narrow row cotton with a full irrigation regime was 1583 kg/ha, the average lint yield from a limited irrigation regime was 1423 kg/ha and the average lint yield from a treatment with no postplant irrigation (fully recharged soil profile at planting) was 601 kg/ha. The full irrigation regime resulted in a dry matter production of approximately 16 t/ha while the limited irrigated regime produce 11 t/ha and the no-postplant irrigation regime produced 7 t/ha of dry matter. The fiber quality results indicated significant (0.05 level) differences only in 50% span length and micronaire, with the 2.5% span length, uniformity index, elongation and strength indicating no difference.Cotton lint yield was found to be directly related to total evapotranspiration although the relationship was slightly non-linear while dry matter yield was found to be linearly related to evapotranspiration. Both lint and dry matter yield were found to have a linear relationship to estimated transpiration from the water balance model calculations.Contribution from the Unived States Department of Agriculture, Agricultural Research Service, Western Region and the University of California     

Assessing impacts of surge-flow irrigation on water saving and productivity of cotton

To improve water saving and conservation in irrigated agriculture, a range of field evaluation experiments was carried out with various furrow irrigation treatments in cotton fields to estimate the possibilities of improving furrow irrigation performances under conditions of Central Fergana Valley, Uzbekistan. The research consisted in comparing surge and continuous-flow in long furrows and adopting alternate-furrow irrigation. The best results were achieved with surge-flow irrigation applied to alternate furrows. Field data allowed the calibration of a surface irrigation model that was used to identify alternative management issues. Results identified the need to better adjust inflow rates to soil infiltration conditions, cut-off times to the soil water deficits and improving irrigation scheduling. The best irrigation water productivity (0.61 kg m⁻³) was achieved with surge-flow on alternate furrows, which reduced irrigation water use by 44% (390 mm) and led to high application efficiency, near 85%. Results demonstrated the possibility for applying deficit irrigation in this region.     

On-farm water management in saline groundwater area under scarce canal water supply condition in the Northwest India

The study investigates the possibility of enhancing crop water productivity in the parts of Northwest India where groundwater quality is marginal and canal water supply is severely scarce. Soil, Water, Atmosphere and Plant (SWAP) model was calibrated and validated in three farmers’ fields with varying canal water availability and groundwater quality in the Kaithal Irrigation Circle of the Bhakra Canal system, Haryana. On the basis of predicted and observed soil water content, pressure heads, salt concentration at 2 week intervals and crop yields, the model was found suitable for use in the region. A few nomographs were prepared to provide a graphical method to predict the effect of different combinations of water quality and depth of water application on crop yield and soil salinity and to help develop some guidelines to the farming community. Water management alternatives at the field level were suggested to increase the yield and to maintain soil salinity below threshold level. The application of frequent irrigation in precisely leveled field would help in achieving 10% higher yield even when saline groundwater of 11 dS/m is used for irrigation.     

西北内陆旱区洋葱耗水规律试验研究

以白皮洋葱为试材,利用称量式蒸渗仪灌水试验,研究了不同灌水量及土壤含盐量对洋葱的耗水规律、产量和水分利用效率的影响。供试土壤分别为低盐土和高盐土,低盐土在鳞茎膨大期设置3种灌水处理,其对应的灌水下限分别为0~30 cm土层土壤含水率达到田持的80%、70%和60%,其他生长期和高盐土的全生育期灌水下限均为田持的80%。研究结果表明,鳞茎膨大期是洋葱的关键需水期;洋葱作物系数立苗期为0.50,发叶期为1.00,鳞茎膨大期为1.50,成熟期为1.25。低盐土的中水处理洋葱可获得最大产量、水分利用效率和较大的灌溉水利用效率;水分和盐分胁迫对洋葱的产量和耗水具有明显的影响。在石羊河流域洋葱鳞茎膨大期,0~30 cm土层土壤灌水下限为田持的70%左右是较适宜的灌水方案。