Optimization of water and nitrogen management to improve seed cotton yield, water productivity and economic benefit of mulched drip-irrigated cotton in southern Xinjiang, China

Water shortage has seriously hampered the agricultural development in Xinjiang of China. Meanwhile, unreasonable drip fertigation strategy exacerbates the water shortage and pollutes the environment in this region. A two-year experiment of drip-irrigated cotton was conducted in 2018 and 2019 to research the responses of cotton growth, seed cotton yield, water and nitrogen use efficiency and economic benefit to various drip fertigation strategies in southern Xinjiang of China. The main-plots comprised of four irrigation amounts, i.e., 60%ETc-W0.6 (ETc was the crop evapotranspiration.), 80%ETc-W0.8, 100%ETc-W1.0 and 120%ETc-W1.2, and the sub-plots comprised of four nitrogen rates, i.e., 250 kg N ha−1-N250, 300 kg N ha−1- N300, 350 kg N ha−1- N350, and 400 kg N ha−1- N400. In this study, we found that increasing irrigation amount improved the growth and production of cotton, but the difference in seed cotton yield under W1.0 and W1.2 treatments was insignificant. Increasing nitrogen application had a promoting impact on cotton production, especially under water stress conditions. Increasing irrigation amount reduced water productivity (WP) and irrigation water productivity (IWP) but improved nitrogen partial factor productivity (PFPN), which had a negative correlation with increasing nitrogen rate. A quadratic relation between economic benefit and irrigation and nitrogen supplies was found, and the highest economic benefit was achieved under W1.0N350. The multiple regression and spatial analysis were used to search the best combination of water and nitrogen regimes, i.e., irrigation amount of 275 mm ∼ 304 mm with nitrogen rate of 290 kg ha−1 ∼ 440 kg ha−1, in which over 90% of the highest seed cotton yield, WP and economic benefit can be achieved simultaneously. Meanwhile, the results of Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) showed that the optimal treatment was W1.0N350, which was consistent with the results of multiple regression and spatial analysis.