Spatial variability of soil carbon to nitrogen ratio and its driving factors in Ili River valley, Xinjiang, Northwest China

Soil carbon to nitrogen (C/N) ratio is one of the most important variables reflecting soil quality and ecological function, and an indicator for assessing carbon and nitrogen nutrition balance of soils. Its variation reflects the carbon and nitrogen cycling of soils. In order to explore the spatial variability of soil C/N ratio and its controlling factors of the Ili River valley in Xinjiang Uygur Autonomous Region, Northwest China, the traditional statistical methods, including correlation analysis, geostatistic alanalys and multiple regression analysis were used. The statistical results showed that the soil C/N ratio varied from 7.00 to 23.11, with a mean value of 10.92, and the coefficient of variation was 31.3%. Correlation analysis showed that longitude, altitude, precipitation, soil water, organic carbon, and total nitrogen were positively correlated with the soil C/N ratio (P < 0.01), whereas negative correlations were found between the soil C/N ratio and latitude, temperature, soil bulk density and soil pH. Ordinary Cokriging interpolation showed that r and ME were 0.73 and 0.57, respectively, indicating that the prediction accuracy was high. The spatial autocorrelation of the soil C/N ratio was 6.4 km, and the nugget effect of the soil C/N ratio was 10% with a patchy distribution, in which the area with high value (12.00–20.41) accounted for 22.6% of the total area. Land uses changed the soil C/N ratio with the order of cultivated land > grass land > forest land > garden. Multiple regression analysis showed that geographical and climatic factors, and soil physical and chemical properties could independently explain 26.8%and 55.4% of the spatial features of soil C/N ratio, while human activities could independently explain 5.4% of the spatial features only. The spatial distribution of soil C/N ratio in the study has important reference value for managing soil carbon and nitrogen, and for improving ecological function to similar regions.