Modelling nitrogen leaching and ammonia volatilization from wither wheat fields in the Yellow River Basin using the WHCNS model

【Objective】 Nitrogen leaching and ammonia volatilization are major pathways for nitrogen loss in agricultural systems, influenced by various factors. This study investigates the effect of water and nitrogen management practices on these nitrogen loss pathways in winter wheat fields in the Yellow River Basin. 【Method】 The WHCNS model was used in our study. Field-measured data were used to calibrate the model, which was then used to simulate nitrogen leaching and ammonia volatilization during the greening and ripening stages of the winter wheat. The simulation results were analysed to optimize water and nitrogen management practices using the CRITIC-TOPSIS method. 【Result】 The consistency indices and coefficients of determination between the simulated and measured soil water content, nitrate nitrogen and ammoniacal nitrogen in the 0-100 cm soil layer varied from 0.842 to 0.973 and 0.666 7 to 0.988 4, respectively. Following nitrogen fertilization, the cumulative nitrate nitrogen loss via leaching from the soil increased first and then decreased with the increase in the number of irrigations in the first seven days after the fertilization. In the first seven days after the fertilization, ammonia volatilization accounted for 93.0% to 98.2% of the total ammonia volatilization. Our simulated results showed that the optimal water and nitrogen management for winter wheat in the region was to apply 220 kg/hm2 of nitrogen fertilizer and keep soil water content in the root zone above 70% of the field capacity, achieving a grain yield of 8 185.30 kg/hm2. The associated nitrate nitrogen loss was 12.011 kg/hm2 and ammonia volatilization was 1.969 kg/hm2. 【Conclusion】 For winter wheat in the Yellow River Basin, the optimal irrigation and nitrogen fertilization is to apply 220 kg/hm2 of nitrogen fertilizer and maintain soil moisture at no less than 70% of the field capacity.