Optimal irrigation amount and nitrogen rate improved seed cotton yield while maintaining fiber quality of drip-fertigated cotton in northwest China

Abstract

Improving the quality of cotton fiber is an important way to increase the competitiveness of cotton in the international market. However, how to improve fiber quality as much as possible without significantly reducing seed cotton yield is still a challenge to the cotton industry. A two-year field experiment was conducted in 2018 and 2019 to investigate the effects of irrigation amount and nitrogen rate on seed cotton yield and fiber quality traits of drip-fertigated cotton in northwest China. A comprehensive evaluation model was also developed to determine the optimal supply range of water and nitrogen to simultaneously improve seed cotton yield and fiber quality. There were four irrigation amounts (W0.6-60 % ETc, W0.8-80 % ETc, W1.0-100 % ETc and W1.2-120 % ETc, ETc was the crop evapotranspiration) and four nitrogen rates (N250-250 kg N ha−1, N300-300 kg N ha−1, N350-350 kg N ha−1 and N400-400 kg N ha−1). Increasing irrigation amount and nitrogen rate had positive effects on seed cotton yield. However, there was no significant difference in seed cotton yield between W1.0 and W1.2 and between N350 and N400. The optimal seed cotton yield was obtained under W1.0N350 in both 2018 (6655.58 kg ha−1) and 2019 (6309.3 kg ha−1). Water use efficiency (WUE) increased with the increase of nitrogen rate, and decreased with the increasing irrigation amount. Nitrogen partial factor productivity (PFPN) increased with the increase of irrigation amount, and decreased with the increasing nitrogen rate. There was a positive correlation between irrigation amount and fiber length, fiber strength, fiber quality index (FQI) and textile parameter, but a negative correlation with micronaire and short-fiber index. Fiber length, fiber strength, FQI and textile parameter first increased and then decreased with the increasing nitrogen rate. Irrigation amount and nitrogen rate had no significant effect on maturity index. There were strong correlations between the results of various evaluation methods, but the ranking differed among the methods. Based on the comprehensive evaluation model, the optimal combination of irrigation amount and nitrogen rate was W1.0N350. Through the combination of multiple regression and spatial analysis, the optimal supply range of irrigation amount of 334∼450 mm and nitrogen rate of 320∼400 kg ha−1was able to obtain over 90 % of the optimal seed cotton yield and 80 % of the optimal fiber quality.