VARIATIONS OF SOIL ORGANIC CARBON FOLLOWING LAND USE CHANGE ON DEEP-LOESS HILLSOPES IN CHINA

Land use change is a key factor driving changes in soil organic carbon (SOC) around the world. However, the changes in SOC following land use changes have not been fully elucidated, especially for deep soils (>100 cm). Thus, we investigated the variations of SOC under different land uses (cropland, jujube orchard, 7-year-old grassland and 30-year-old grassland) on hillslopes in the Yuanzegou watershed of the Loess Plateau in China based on soil datasets related to soils within the 0-100cm. Furthermore, we quantified the contribution of deep-layer SOC (200-1,800 cm) to that of whole soil profiles based on soil datasets within the 0-1,800 cm. The results showed that in shallow profiles (0-100 cm), land uses significantly (p < 0.05) influenced the distribution of SOC contents and stocks in surface layer (0-20 cm) but not subsurface layers (20-100 cm). Pearson correlation analysis indicated that soil texture fractions and total N were significantly (p < 0.05 or 0.01) correlated with SOC content, which may have masked effects of land use change on SOC. In deep profiles (0-1,800 cm), SOC stock generally decreased with soil depth. But deep soils showed high SOC sequestration capacity. The SOC accumulated in the 100-1,800 m equalled 90.6%, 91.6%, 87.5% and 88.6% of amounts in the top 100 cm under cropland, 7-year-old grassland, 30-year-old grassland and jujube orchard, respectively. The results provide insights into SOC dynamics following land use changes and stressed the importance of deep-layer SOC in estimating SOC inventory in deep loess soils. Copyright (C) 2017 John Wiley & Sons, Ltd.