Effects of irrigation and nitrogen levels on yield and water-nitrogen-radiation use efficiency of drip-fertigated cotton in south Xinjiang of China

Xinjiang is the greatest cotton production region in China, which often suffers from limited water resources and over-application of water and nitrogen in cotton production. Improving the utilization efficiency of water, nitrogen and light resources is crucial to sustain cotton production in this region. A two-season (2020 and 2021) field experiment was performed in south Xinjiang of China to investigate the impact of irrigation and nitrogen levels on seed cotton yield, water use efficiency (WUE), nitrogen remobilization efficiency, nitrogen use efficiency, and radiation use efficiency (RUE). The experiment included three irrigation levels (W1: 60% ETc, W2: 80% ETc, W3: 100% ETc; ETc was crop evapotranspiration) and four nitrogen levels (N0: 0 kg ha−1, N200: 200 kg ha−1, N300: 300 kg ha−1, N400: 400 kg ha−1). The results indicated that both irrigation and nitrogen levels significantly influenced seed cotton yield, WUE, irrigation water use efficiency (IWUE), nitrogen remobilization, agronomic nitrogen use efficiency (aNUE), nitrogen recovery efficiency (NRE), physiological nitrogen use efficiency (pNUE), light interception fraction (fPAR) and RUE. Increasing irrigation level enhanced both dry matter accumulation and seed cotton yield, which increased and then declined with increasing nitrogen level. The N300 improved WUE and IWUE by 31.81% and 39.88% compared to N0, respectively. Greater irrigation and N levels enhanced post-bolling plant nitrogen uptake and pre-bolling nutrient nitrogen remobilization. The W3 improved aNUE by 53.22%, NRE by 33.77%, and pNUE by 9.13% compared to W1. With the increasing irrigation level, fPAR and RUE increased, whereas they increased and then declined with increasing nitrogen level. In comparison to W1N0, W3N300 increased IPAR and RUE by 26.25% and 76.24%, respectively. The entropy-TOPSIS analysis showed that W3N300 obtained the highest comprehensive evaluation index. Compared with the local irrigation amount of 560 mm and nitrogen level of 400 kg ha−1, W3N300 increased seed cotton yield by 21.41%, IWUE increased by 71.76%, and saved irrigation water and nitrogen by 29.10% and 24.05%, respectively. An irrigation level of 100% ETc combined with a nitrogen level of 300 kg ha−1 was recommended to enhance seed cotton yield and improve water-nitrogen-radiation use efficiency in south Xinjiang of China. This study can provide important information for improving seed cotton yield and resources use efficiency in south Xinjiang of China and maybe other regions with similar climates.