Characteristics and Influencing Factors of Soil Nitrogen in Cropland Soil Across the Sichuan Basin

Objective The aims were to investigate the spatial distribution characteristics of soil nitrogen and its relationship with various influencing factors in regional cultivated land, in order to guide precision fertilization and to protect the ecological environment.

Methods Based on 4,409 topsoil (0 ~ 20 cm) samples from cultivated land, this study employed general statistical methods, ANOVA, and correlation analysis to examine the spatial distribution patterns of soil nitrogen and its influencing factors in the Sichuan Basin. A random forest model was further applied to evaluate the relative importance of different factors.

Results The mean contents of total nitrogen and alkali-hydrolyzable nitrogen in the topsoil were 1.43 g kg⁻¹ and 113.85 mg kg⁻¹, both at a moderate level (Grade III). The coefficients of variation were 34.27% and 38.38%, indicating moderate spatial variability. The spatial distribution of total nitrogen and alkali-hydrolyzable nitrogen showed consistent patterns, generally characterized by lower values in the central basin and higher values in the surrounding mountainous areas. The random forest model revealed that climate and soil texture were the most critical factors influencing the spatial distribution of soil nitrogen, whereas anthropogenic factors had a relatively minor impact compared to natural factors.

Conclusion To enhance the effectiveness and precision of straw returning and fertilization, soil texture and climatic conditions should be comprehensively considered. In regions with higher soil nitrogen content (e.g., the Minjiang River Basin), nitrogen fertilizer application should be controlled to minimize environmental risks.