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

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 (884-999%) 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<001) correlated to TN, and positively (significant at p<005) correlated to elevation at all soil depths. Compared to the reforested area, C:N was typically greater in the agricultural area in the 20-60cm depth. The planting of soybean (Glycine max L) can significantly increase the C:N at the 40-50cm depth. C:N was higher in cross-slope tillage than in down-slope tillage, especially at soil depths of 40-50cm. Generally, topographical factors, land use, crop planting and tillage methods can effectively influence the spatial heterogeneity of C:N in this watershed. Copyright (c) 2015 John Wiley & Sons, Ltd.