Profile stock of soil organic carbon and distribution in croplands of Northeast China

Soil organic carbon (SOC) stock is one of the most important carbon (C) reservoirs on the Earth and plays a vital role in the global climate change. However, SOC stock at a regional scale is still uncertain due to the lack of soil bulk density data, differences in sample depth, geography, and soil properties. Based on data from 78 soil profiles, we estimated SOC density (SOCD) and its distribution at 0-100 cm depth of croplands in three typical Counties (Lindian, Hailun and Baoqing Counties) in Northeast China. Soil organic carbon content and variations significantly decreased with increased soil depth. The SOCD in 100-cm depth ranged from 52.3 to 323.1 Mg ha(-1), with an average of 163.6 Mg ha(-1). The SOCD in the top 20 cm accounted for 32.8% of that in 100 cm soil profile. A good mathematical equation between SOCD of 0-20 cm and 0-100 cm would be a useful tool to estimate SOCD in soil profiles. In addition, soil depth, bulk density, soil pH, and elevation were significantly correlated with SOC content. Regression of SOC in the data set to individual factors (soil depth, BD, soil pH, clay content, and elevation) is relevant to understand how C changes over time and depth.