Optimization of Water and Nitrogen Regime Based on AquaCrop Model for Drip Irrigation Cotton Under Nitrogen Reduction Conditions in Northern Xinjiang

Abstract

[Objective] This study was aimed to test the applicability of the AquaCrop model for simulating the growth and production of drip-irrigated cotton under nitrogen-reducing conditions in the northern border, and to investigate the optimal nitrogen-reducing and irrigation regimes during the reproductive period of cotton. [Methods] Through the field trials in 2022 and 2023, we clarified the effects of four nitrogen application levels (conventional nitrogen application, nitrogen reduction of 10%, nitrogen reduction of 20%, and nitrogen reduction of 30%), and three irrigation schedules (488, 444, and 400 mm) on cotton yield, water and nitrogen use efficiency, and soil nutrient content; we used measured data from the treatments to determine and validate the parameters of the model, and then simulated the model with the calibrated model. Cotton yield and water and nitrogen use efficiencies were simulated with the calibrated model under six combinations of nitrogen application levels (conventional nitrogen application, nitrogen reduction of 6%, nitrogen reduction of 12%, nitrogen reduction of 18%, nitrogen reduction of 24%, and nitrogen reduction of 30%), and six combinations of irrigation levels (300, 360, 420, 480, 540, and 600 mm), and the optimal water and nitrogen combinations were screened out by the comprehensive evaluation method. [Results] Nitrogen reduction and irrigation quota together had a significant effect on cotton yield, water and nitrogen use efficiency and soil nutrients. Nitrogen fertilizer reduction can be achieved by appropriately increasing the irrigation quota to stabilize cotton yield; Under the same nitrogen application, appropriately reducing the irrigation quota improved water use efficiency; Under the same irrigation quota, appropriately reducing the nitrogen application improved nitrogen fertilizer bias productivity; A 10% increase in the conventional irrigation quota (W1N1) when applying conventional nitrogen effectively improved the nutrient content of the tillage layer of the soil. The simulation and measurement results showed that each evaluation index of canopy cover and above-ground biomass of the 2-years experimental treatments satisfied the coefficient of determination (R2)≥ 0.936, the root mean square error (NRMSE) ≤ 40.58%, and the Nash coefficient (ENS)≥ 0.72; And each evaluation index of yield and water-use efficiency satisfied the coefficient of determination R2≥0.87, NRMSE ≤ 4.29%, and ENS≥0.81; The model achieved a better simulation effect. [Conclusion] Based on the scenario simulation under 36 combinations of nitrogen reduction and irrigation, and considering the yield, water and nitrogen utilization efficiency and the actual production cost, the nitrogen reduction irrigation system with 12% nitrogen reduction and 360 mm irrigation quota is recommended to be adopted in the northern border region. The study can provide experience for the application of the AquaCrop model under different fertilizer and irrigation regimes in the future and provide a theoretical basis and scientific guidance for the improvement of water and nitrogen fertilizer use efficiency during cotton cultivation in arid regions.

Keywords

• nitrogen fertilizer reduction
• aquacrop
• cotton
• water use efficiency
• nitrogen bias productivity
• water nitrogen regime