Spatial Heterogeneity of Soil C:N Ratio in a Mollisol Watershed of Northeast China

Abstract

Abstract The spatial variability of the soil C:N ratio (C:N) influences C and N leaching and basic fertility in the field. This paper aims to identify the spatial heterogeneity of C:N in a Mollisol watershed of Northeast China and determine the main mechanisms that drive these differences. A random sampling method was used, with both geostatistical and traditional analysis being used to describe the spatial distribution of the C:N at various depths. C:N was also compared between slope position, previous vegetation and tillage methods in the watershed. The horizontal distribution of the C:N was mainly influenced by structural factors (88·4–99·9%) and often gradually deceased along the hydrographic flow direction, becoming lowest at the watershed outlet. The C:N increased as soil depth increased at all slope positions, and was higher on the back slope than on summit slope, followed by bottom slope in all soil depths. C:N was negatively (significant at p < 0·01) correlated to TN, and positively (significant at p < 0·05) correlated to elevation at all soil depths. Compared to the reforested area, C:N was typically greater in the agricultural area in the 20–60 cm depth. The planting of soybean ( Glycine max L) can significantly increase the C:N at the 40–50 cm depth. C:N was higher in cross‐slope tillage than in down‐slope tillage, especially at soil depths of 40–50 cm. Generally, topographical factors, land use, crop planting and tillage methods can effectively influence the spatial heterogeneity of C:N in this watershed. Copyright © 2015 John Wiley & Sons, Ltd.