Improvement of saline water use under drip irrigation system

The use of saline water in a surface drip irrigation system has several advantages over other irrigation methods. Variables affecting soil water content (θw) and soil salinity (ECw), including irrigation regimes and crop growth stages, were investigated at different radial distances from the emitter at a depth of 10 cm. Three irrigation regimes were applied: the first irrigation regime (ETc) was based on daily crop–water requirement while the two others were based on ETc + 20% and + 40% (1.2ETc and 1.4ETc, respectively). The simultaneous distribution of θw and ECw under drip irrigation was measured by time domain reflectometry (TDR). The results indicated that ECw increased in the order ETc > 1.2ETc > 1.4ETc and also with crop growth stages. For all the irrigation regimes and all crop growth stages, the maximum θw and minimum ECw occurred simultaneously at a radial distance of 10 cm (r10) from the emitter. The simultaneous occurrence of maximum θw and minimum ECw at the 20 cm radial distance from emitter (r20) was noted only for 1.4ETc. It is suggested that irrigation should commence at different times before noon, depending on the crop growth stage, so that maximum θw (minimum ECw) will coincide with maximum evapotranspiration (ETo). The influence of θw on ECw was restricted to a small radius of about 0–20 cm from the emitter. Beyond this range, increases in θw did not significantly affect ECw. The first irrigation regime (ETc) was found unsuitable for irrigation with saline water. Emitter spacing of 25 and 30 cm were suggested for 1.2ETc and 1.4ETc to minimize ECw levels along the lateral pipe. Based on the crop–water production function the yield reduction due to saline water use was minimum under 1.4ETc, which cannot be improved by increasing the amount of irrigation water.