Objectives Understanding the spatial variation of soil total nitrogen, organic carbon and ratio of carbon to nitrogen and their influencing factors is the premise and foundation of soil carbon and nitrogen regulation.

Methods This study took a case of Fengcheng City, where 139 surface soil data were obtained in 2018 through field sampling. We used Geostatistics, Ordinary Kriging interpolation and other methods systematically to analyze the spatial variation characteristics and influencing factors of total nitrogen, organic carbon and ratio of carbon to nitrogen of cultivated land in typical hilly areas in south China.

Results Soil total nitrogen (TN) in the study area ranged from 0.74 g/kg to 3.80 g/kg, soil organic carbon (SOC) ranged from 8.14 g/kg to 36.67 g/kg, and soil carbon to nitrogen ratio (C/N) ranged from 6.31 to 15.15, with mean values of 2.24 g/kg, 22.52 g/kg and 10.15, respectively. The coefficients of variation of TN, SOC and C/N were 25.45%, 26.24% and 14.38% respectively, showing moderate spatial variation. The results of semi-variance analysis showed that the Nugget effect of TN, SOC and C/N was 44.44%, 56.97% and 19.57%, respectively, indicating that the spatial distribution of TN, SOC and C/N was affected by both structural factors and random factors. The results of Ordinary Kriging interpolation showed that soil TN and SOC in spatial distribution were similar in the study area, and generally showed a trend of decreasing from the middle to the north and south. The spatial distribution of soil C/N was different from that of TN and SOC, with the general trend of higher in the west and lower in the east. Stepwise regression analysis showed that soil parent material, soil type, soil pH, nitrogen fertilizer application amount and soil texture had significant effects on soil TN, soil parent material, soil type and soil pH had significant effects on SOC, and soil type had significant effects on soil C/N (P<0.01).

Conclusions The independent interpretation of soil TN and SOC by parent materials is the highest which are 28.1% and 23.2%, respectively. The independent interpretation ability of soil type to soil C/N in the study area could reach 13.2%. Therefore, the soil parent material is the main factor causing the spatial variation of total nitrogen and organic carbon in the study area, while the soil type is the main factor causing the spatial variation of ratio of carbon to nitrogen in the soil of this study area.