Soil salinity, leaching, and cotton growth as affected by saline water drip irrigation and N fertigation

Saline water (SW) irrigation is necessary in parts of the world where supplies of good quality water are limited. The aim of this study was to learn more about the use of saline irrigation water in drip-irrigated cotton. Therefore, a 5-year field experiment consisted of a 3 × 2 factorial complete randomized block design with three levels of irrigation water salinity (0.35, 4.61, and 8.04 dS m−1) and two N application rates (240 and 360 kg N ha−1) was carried out in arid regions of northwestern China. The results indicated that drip irrigation with SW (4.61 or 8.04 dS m−1) increased average soil water content and average soil salinity in the 0–100 cm depth. SW irrigation increased leachate –N concentrations. Nitrogen rate significantly affected leachate volume and salt concentration in some years; however, the trends were inconsistent. The treatment with 8.04 dS m−1 irrigation water significantly reduced cotton growth, yield, and N uptake in all the five cropping seasons. In contrast, the treatment with 4.61 dS m−1 water increased cotton growth, yield, and N uptake in the first year, but in the third, fourth, and fifth years, cotton growth, yield, and N uptake were significantly lower in the treatment with 4.61 dS m−1 water than in the treatment with 0.35 dS m−1 water. Cotton growth and yield increased as N application rate increased; however interactive effects between water salinity and N rate on cotton growth and yield were generally not significant. We conclude that drip irrigation with SW (EC>4.6 Ds m−1) reduces cotton yield and increases the risk of salt and –N leaching to groundwater. Additional N fertilizer input may overcome some of the negative effects of salinity on cotton growth, but also increases the potential risks for nitrate leaching.