Suitable fertilizer application depth can increase nitrogen use efficiency and maize yield by reducing gaseous nitrogen losses

Abstract During spring maize production, nitrogen is lost in the form of gaseous N because of shallow fertilizer application, which leads to a low nitrogen use efficiency (NUE). However, the specific effects of the fertilization depth on the losses of gaseous nitrogen (NH3 and N2O) from the soil are unclear. During 2019 and 2020, we established a field experiment with spring maize (Zea mays L.) to test the effects of different fertilizer placement depths of 5 cm (D5), 15 cm (D15), 25 cm (D25), and 35 cm (D35) on the NUE and gaseous nitrogen loss intensity (GNLI). The losses of N in the forms of NH3 and N2O were measured throughout the maize growth period. The trends in terms of NH3 volatilization, N2O emissions, and nutrient uptake were similar for different fertilizer depths during 2019 and 2020. NH3 was the main form of gaseous nitrogen lost compared with N2O. The ratio of gaseous nitrogen loss relative to nitrogen application (GNLR) was 13.11%, and the GNLI was 3.43 g N kg−1 grain under D5. Compared with D5, the GNLR values were 34.77%, 54.67%, and 70.23% lower under D15, D25, and D35, respectively, and the GNLI values decreased significantly by 31.27%, 49.91%, and 54.12%. The nitrogen uptake amounts by maize were 8.07% and 17.41% higher under D15 and D25 during the two years, respectively, while the NUE values were 17.79% and 38.37% higher, and the maize yields were 5.68% and 13.83% greater compared with D5. Structural equation modeling showed that 79% of the NUE could be explained by the differences in the fertilization depth. Therefore, deep-band placement fertilizer at a depth of 25 cm can reduce GNLI by decreasing the NH4+-N concentration in the surface layer to ultimately increase the nitrogen uptake, NUE, and maize yield. Deep-band placement fertilizer is a suitable method for supporting the development of agricultural ecosystems.