Cotton growth and the fate of N fertilizer as affected by saline water irrigation and N fertigation in a drip-irrigated field

Abstract

ABSTRACTThe objective of this two-year field experiment was to study the effects of irrigation amount, N rate, and irrigation water salinity on cotton growth and the fate of N fertilizer. The movement of N through the plant-soil system was traced using 15N-labeled urea. The study consisted of twelve treatments, including two irrigation amounts (405 and 540 mm, I405 and I540, respectively); two N application rates (240 and 360 kg N/ha, N240 and N360, respectively); and three irrigation water salinity levels [0.35, 4.61 and 8.04 dS/m, representing fresh water (FW), brackish water (BW), and saline water (SW), respectively]. A randomized complete block design was used with three replications. The results showed that cotton biomass, N uptake, and yield increased as irrigation amount and N amount increased; however, all three variables were significantly less in SW than in FW and BW. Plant 15N recovery rates were greater (i) in the I540 treatments than in the I405 treatments and (ii) in the N360 treatments than in the N240 treatments. Plant 15N recovery rates in BW were 7.98% and 30.01% greater than those in FW and SW, respectively. Residual soil 15N increased as N fertilizer amount increased but declined as irrigation amount increased. Residual soil 15N in BW and SW was 6.02% and 21.44% greater, respectively, than in FW. Total 15N recovery was significant greater in BW than in FW and SW. The 15N leaching losses increased significantly with increases in irrigation amount, irrigation water salinity, and N rate. Our study suggests that if appropriate amounts of irrigation water and N fertilizer are used, then brackish irrigation water (4.61 dS/m) will not affect cotton growth, yield and N recovery. In contrast, saline irrigation water (EC > 8 dS/m) reduces cotton growth, yield, and N use efficiency.