Comprehensive assessment of nitrogen fertilizer management for maize in Northeast rainfed region

Objectives We adopted a comprehensive evaluation method to evaluate the current nitrogen fertilizer management for maize considering yield, economic benefit, N fertilizer efficiency and the environment.

Methods Field experiments were carried out in the rainfed region of Northeast China in 2018 and 2019 with five N application rates: N0, N75, N150, N225 and N300 (kg/hm²). Maize yield, nitrogen efficiency and soil N content in 0–100 cm depth were measured at the harvesting stage. The relationship of N application rate with maize yield, marginal benefit, N recovery rate, N agronomy efficiency, partial factor productivity of N fertilizer, N physiological use efficiency, soil N apparent balance and inorganic N accumulation was determined. The highest yield and profit but the least farmland environment risk was set as the top target layer, under it were the four criterion layers, including yield, profit, N fertilizer efficiency and environmental risk. Each criterion layer was further divided into element layers. The weight coefficient of each criterion layer and element layer was determined according to experimental data, and all of the element data were normalized for calculate the comprehensive evaluation scores of each treatment.

Results The four criterion layers and their weight coefficients were: yield 0.39, profit 0.29, N efficiency 0.10 and environmental risk 0.22, respectively. And there was a total of eight element layers and their weight coefficients were yield 0.39, marginal benefit 0.29, N recovery 0.025, N agronomic efficiency 0.025, N partial productivity 0.025, N physiological utilization efficiency 0.025, soil nitrogen apparent balance 0.07, and soil inorganic nitrogen accumulation 0.15, respectively. According to the weight coefficient, the comprehensive scores of nitrogen application rate N225 were 0.81 and 0.92 in 2018 and 2019; for N150 were 0.67 and 0.78; for N75 was 0.67 in both years; for N300 were 0.55 and 0.53; and for N0 was 0.15 in both years. The N application rate with score higher than 0.8 was deemed optimal for recommendation, which was 225 kg/hm² in 2018 and 186–225 kg/hm² in 2019.

Conclusions Through layering the top target into criterion layer and further into element layers, the effect of each layer of the target was fully considered by its weight coefficient. The optimal N application rate was evaluated comprehensively, hence could meet the requirement for maize yield and profit, and the fertilizer efficiency and environmental safety.