Abstract:In order to clarify the optimal film mulching type and nitrogen application system in arid areas, a two-year film mulching farmland fertilization experiment was conducted at Muleitan Water-saving Experimental Station in the Hetao Irrigation District, Inner Mongolia. Three mulching treatments were set at high nitrogen level (conventional nitrogen application 336 kg/hm2), including plastic film (PFM3), biodegradable film (BFM3) and no film mulching (NFM3); at the same time, three nitrogen levels were set up under biodegradable film mulching, including medium nitrogen (BFM2:276 kg/hm2), low nitrogen (BFM1:216 kg/hm2) and no nitrogen (BFM0:0 kg/hm2), making up to a total of six treatments. The DNDC model was calibrated and verified by the observed values of two-year yield, nitrogen uptake and leaching, and the film type and fertilization system were optimized based on the improved TOPSIS method. The results showed that the DNDC model was sensitive to crop growth and nitrogen migration under different film mulching and nitrogen regulations. The simulated EF and R2 of yield, nitrogen uptake and leaching were greater than 0.83, NRMSE were less than 20%, which could predict and evaluate crop productivity and resource utilization. With the increase of nitrogen application amount, the nitrogen leaching of each mulching treatment increased linearly. When nitrogen application amount increased to 106 kg/hm2, nitrogen use efficiency reached the peak; when the nitrogen application amount increased to 256 kg/hm2, the yield of mulching treatments did not change significantly. At the same time, the net income of BFM reached the maximum, but the cost of biodegradable film was high, which resulted in a net income of 6.84% lower than PFM and 3.17% higher than NFM. There was no significant difference in nitrogen leaching, use efficiency and yield between biodegradable film mulching and plastic film mulching, which were significantly higher than no film mulching, and the average increase from 8.22% to 26.69%. The improved TOPSIS method was used to comprehensively evaluate the yield, nitrogen leaching, use efficiency, residual film amount, and net income. The results showed that the application of 231 to 256 kg/hm2 nitrogen fertilizer was the most reasonable fertilization system under biodegradable film mulching in arid areas.