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

To explore the input threshold of a one-time application of N fertilizer that considers maize yield and environmental effects in the black soil region of Northeast China, this study established an eight-year field experiment in the 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 a one-time application of N fertilizer (common urea plus controlled-release N fertilizer at a N ratio of 4∶6). Six N fertilizer application treatments were established: 0, 70, 140, 210, 280, and 350 kg∙hm⁻², labeled as N0, N70, N140, N210, N280 and N350, respectively. The results showed that the eight-year average yield increased by 63.8%–188.8% under N fertilizer application treatments compared with no N fertilizer, and a significant difference was observed (P<0.05). The yield advantage under N fertilizer application treatments was mainly attributed to the increased grains per ear and 100-kernel weight of maize. The maize yield was an upward trend with increased N application rates, reaching the yield platform under 210 kg∙hm⁻² of N fertilizer rates. With this N fertilizer rate, the average yield over eight years was 11 668 kg∙hm⁻². The apparent N recovery efficiency (REN), N agronomic efficiency (AEN), and N partial factor productivity (PFPN) all declined with increasing N application rates. The NO₃⁻-N contents in the 0–100 cm soil layer increased with increasing N application years and N fertilizer rates. The NO₃⁻-N content in the N210 treatment was similar to the initial value of the experiment. In the eight-year experiment, the N balance results showed that N residuals and apparent N loss increased with increasing N fertilizer rates. The residual N in the N210 treatment was similar to the initial values in the experiment. When it reached the yield platform at 208.8 kg∙hm⁻² of N fertilizer rate, maize yield, N recovery efficiency, soil N residuals, and N apparent loss were 11 835 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 for maize yield, N recovery efficiency, and N apparent loss matched well with the observed values under the maximum yield of the N210 treatment. Simultaneously, the residual N was similar to the initial value of the experiment. Within the 95% confidence interval of the N application rate under the theoretical maximum yield, the optimum N application rate was calculated at 198−219 kg∙hm⁻². In conclusion, the N application range of 198−219 kg∙hm⁻² obtained higher maize yield and N use efficiency, as well as 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 an input threshold for the one-time application of N fertilizer that considers maize yield and environmental effects. These results provide a theoretical basis for the one-time application of N fertilizer to maize in the black, thin-layered soil region of Northeast China.