Combination with moderate irrigation water temperature and nitrogen application rate enhances nitrogen utilization and seed cotton yield

To promote the efficient utilization of groundwater and improve nitrogen fertilizer effectiveness, a reasonable range of nitrogen application rates and irrigation water temperature was investigated. A field experiment was conducted in Xinjiang, China, in 2022 and 2023, involving four irrigation water temperature levels (T0: 15 °C, T1: 20 °C, T2: 25 °C, and T3: 30 °C) and three nitrogen application rates (F1: 250 kg ha⁻¹, F2: 300 kg ha⁻¹, and F3: 350 kg ha⁻¹). The results indicated that soil nitrogen content, cotton dry matter weight, cotton nitrogen content, seed cotton yield, and nitrogen partial factor productivity (NPFP) increased with higher nitrogen application rates. However, as irrigation water temperature increased, soil nitrogen content decreased, whereas cotton dry matter weight, cotton nitrogen content, seed cotton yield, and NPFP initially increased before declining. Notably, the maximum yield and NPFP among all treatments were observed in T2F2 (25 °C, 300 kg ha⁻¹), yielding 6652 kg ha^–1 and 6941 kg ha^–1, and in T2F1 (25 °C, 250 kg ha^–1), with 24.20 kg kg^–1 and 25.20 kg kg^–1 in 2022 and 2023, respectively. Furthermore, the optimal range of irrigation water temperature of 23.82–27.41 °C and nitrogen application rate of 276.43–289.23 kg ha^–1 were identified to achieve over 80 % of the highest seed cotton yield and NPFP using multiple regression and spatial analysis methods. This study offers valuable guidance for optimizing irrigation and fertilization strategies to enhance resource efficiency and promote sustainable cotton production in arid regions.