Abstract: A field experiment on manual loessial soil was conducted to study the dynamic changes of NO₃^--N in soil profile, utilization rate of fertilizer N, and relationships between N application rate and soil residual N accumulation during the growth period of summer maize under different N application rates (0, 45, 90, 135, and 180 kg·hm^-2). The results showed that in the whole growth period of summer maize, the NO₃^--N concentration in the soil profile was the highest in 0-20 cm layer, and increased with increasing N application rate. The NO₃^--N concentration in 0-60 cm soil layer changed significantly, but no significant change was observed in 60-100 cm soil layer. In the growth season of summer maize, soil NO₃^--N accumulation presented a fluctuated decreasing trend due to the N uptake by crop and the precipitation. The N utilization rate (NUR) increased with increasing N application rate when the application rate was less than 135 kg·hm^-2, but tended to decrease when the application rate exceeded 135 kg·hm^-2. With the increase of N application rate, the N agronomy efficiency (NAE) decreased but the N physiology efficiency (NPE) increased. There was a significant positive correlation between soil residual N accumulation and N application rate (R²=0.957^**,n=5). The grain yield under N application was significantly higher than that without N application (P<0.05), and there existed a significant positive correlation between grain yield and N application rate (R²=0.934^**,n=5). In our experiment, the optimal 〖LM〗application rate of fertilizer N was 135 kg·hm^-2, which could harmonize the relationship between economic benefits and environment.

Key words: Pinus massoniana, C:N:P stoichiometry, red soil erosion degradation