Input threshold of one-time application of nitrogen fertilizer to coordinate maize yield and environmental effects in thin layer black soil region of Northeast China

In order to explore the input threshold of one-time application of N fertilizer that takes into account maize yield and environmental effects in the black soil region of Northeast China, this study sets up an eight-year located field experiment in black thin-layer soil region of Jilin Province (Liufangzi village, Gongzhuling City) from 2016 to 2023. This study revealed the responses of maize yield, N uptake and utilization, soil NO₃^--N content and soil N apparent balance to different nitrogen (N) fertilizer rates under the condition of one-time application of N fertilizer (common urea plus controlled-release N fertilizer in N ratio of 4:6). Six N fertilizer application treatments were designed, including 0 kg∙hm⁻², 70 kg∙hm⁻², 140 kg∙hm⁻², 210 kg∙hm⁻², 280 kg∙hm⁻² and 350 kg∙hm⁻² (recorded as N0, N70, N140, N210, N280 and N350, respectively). The results showed that the eight-year average yield was increased by 63.8%~188.8% under N fertilizer application treatments than no N fertilizer, and there was significant difference (P<0.05). The yield advantage under N fertilizer application treatments was mainly attributed to increased grains per ear and 100-kernel weight of maize. The maize yield was an upward trend with the increase of N application rates, which it reached the yield platform under 210 kg∙hm⁻² of N fertilizer rates. Under this N fertilizer rate, the average yield was 11668 kg∙hm⁻² across eight years. The apparent N recovery efficiency (REN), N agronomic efficiency (AEN), and N partial factor productivity (PFPN) all declined with the increase of N application rates. NO₃^--N contents in 0-100 cm soil layer increased with increase of N application years and N fertilizer rates. Among them, the NO₃^--N content in N210 treatment was similar to the initial value of the experiment. In the eight-year experiment, N balance results showed that the N residuals and N apparent loss increased with the increase of N fertilizer rates. Among them, the N residuals in N210 treatment was similar to the initial value of the experiment. When it reached the yield platform under 208.8 kg∙hm⁻² of N fertilizer rate, maize yield, N recovery efficiency, soil N residuals and N apparent loss were 11835 kg∙hm⁻², 48.2%, 172.3 kg∙hm⁻² and 53.9 kg∙hm⁻² respectively, by simulating between maize yield, N recovery efficiency, soil N residuals, N apparent loss and N application rates, respectively. The calculated theoretical results of the maize yield, N recovery efficiency and N apparent loss matched well with the observed values under the maximum yield of N210 treatment. At the same time, the N residual was similar to the initial value of the experiment. Within the 95% confidence interval of N application rate under the theoretical maximum yield, the optimum N application rate was calculated at the range of 198−219 kg∙hm⁻². In conclusion, the N application range of 198−219 kg∙hm⁻² not only obtained higher maize yield and N use efficiency, but also maintained the basic stability of soil N pools before and after maize harvest, and also reduced N apparent loss to a lower level. Therefore, it can be used as input threshold of one-time application of N fertilizer that takes into account maize yield and environmental effects. This research results can provide a theoretical basis for one-time application of N fertilizer of maize in black thin-layer soil region of Northeast China.