Effects of water salinity and nitrogen rate on yield, WUE and NUE of cotton under drip irrigation with saline water conditions

In arid and semiarid regions, fresh water scarcity and salinity are the serious and chronic problem for agricultural production. The purposes of optimal water and nutrient management are to maximize water and fertilizer use efficiencies and crop production, and to minimize salt accumulation in root zone and groundwater pollution in these regions. In this study, field experiments were conducted to investigate effects of irrigation water salinity and N application rate on yield, water use efficiency (WUE) and nitrogen use efficiency (NUE) of cotton under drip irrigation conditions. The experimental design was a 3 4 factorial with three water salinity levels (EC 0.35, 4.61, and 8.04 dS/m; denoted as SF, SM and SH, respectively) and four N application rates (0, 240, 360, and 480 kg/ha; denoted as N0, N1, N2, and N3, respectively). Results show that the biomass, N uptake, and NUE of cotton are significantly affected by irrigation water salinity, N rate and their interactions and are decreased significantly by the saline water irrigation with the high salinity level (8.04 mS/cm). There are no significant differences for cotton N uptakes and NUEs between SM and SF treatments, while the biomass and yield of the SF treatment are higher than those of the SM treatment. The growth of cotton is promoted by the N fertilization and the biomass, N uptake, and yield are increased, while those effects are decreased with irrigation water salinity level increasing. Water drainage is increased and evapotranspiration is reduced significantly with the increase of irrigation water salinity level, while water drainage is decreased and evapotranspiration is increased significantly with the increase of nitrogen rate. The treatment of SM has the highest WUE, and the treatment of SH has the lowest WUE. WUEs of three water salinity treatments are increased with nitrogen application rate increasing. Therefore, saline water with EC value more than 8 dS/m is not suitable for drip irrigation, but short period saline water irrigation with EC value less than 5 dS/m does not have a severe adverse effect on yield, NUE and WUE of cotton under drip irrigation conditions. Moreover, optional N application can promote cotton growth and increase yield and WUE of cotton.