Changes in organic carbon content of purple soil topsoil and its response to climate warming

Based on data from the Second National Soil Survey in the 1980s, which includes 1, 087 samples, and soil sampling data from the 2010s, which includes 1, 154 samples, this study utilizes geostatistics, analysis of variance (ANOVA), and regression analysis to investigate the changes in topsoil organic carbon (SOC) content in purple soil cropland in the Sichuan Basin over the past 40 years, the influencing factors, and its response to climate warming. The results indicate that the SOC content in the study area increased from 6.97 g·kg^-1 to 9.65 g·kg^-1, with an increase of 2.68 g·kg^-1. The growth rates of organic carbon content varied among different geomorphic zones and secondary river basins. The spatial variability of SOC caused by parent material decreased; SOC increment showed a positive parabolic relationship with temperature, and a negative parabolic relationship with precipitation, altitude, and slope. Under relatively dry conditions (precipitation<1 050 mm), the SOC increment was 1.64 times that under humid conditions (>1 050 mm). The SOC increment initially decreased and then increased with the average annual fertilization rate and crop yield and their growth rates. Additionally, the SOC increment showed similar parabolic trends under different moisture conditions, but SOC under dry conditions was more sensitive to temperature changes, indicating that the response of SOC in purple soil to warming is strongly influenced by moisture conditions and soil characteristics.