Plant and Soil Water Dynamics of Alternate Furrow and Regulated Deficit Irrigation for Two Legume Crops

Water scarcity and severe environmental degradation are causing water managers in Central Asia to reevaluate irrigation water use. In this area, the goal of any intervention must include water conservation without reducing crop productivity. The objective of this study was to evaluate the impact of two irrigation technologies, regulated deficit irrigation and alternate furrow irrigation, on components of the plant-soil water system for common bean and green gram. The use of both deficit irrigation and alternate furrow irrigation resulted in water savings and reduced crop evaporative consumption. The reduction was greater in green gram than common bean when both technologies were used. The pattern of water extraction from the soil profile, when under stress, was different between the crops. Severely stressed common bean extracted more water at 60 cm than non-stressed plants, whereas severely stressed green gram used less water at all depths. Transpiration rates were generally lower in green gram than common bean and decreased in both crops as soil water deficit increased. However, when the soil water was returned to field capacity by irrigation, common bean's water use was higher than the non-stressed condition while green gram's transpiration rate only increased slightly from the before-irrigation value. Collectively, these results indicate distinct crop-dependent responses to soil drying. Use of the FAO water stress coefficient in predicting evapotranspiration under water-limiting conditions appears to overpredict water use for green gram and could lead to over-irrigation; considerable water savings are available for this crop