Distribution of Soil Organic Carbon Fractions as Related to Land Use and Management in the Loess Plateau, Northern China

Organic C in the soil is not a uniform material but rather a complex mixture of plant, animal and microbial residues at different stages of decomposition (Post and Kwon 2000). So the dynamics of soil organic carbon (SOC) is usually described by dividing total SOC into different fractions (Six et al. 2002). Of all the different fractions, density defined fractions (light- and heavy fractions) may relate better to specific functions or processes (O’Hara et al. 2006), and the changes in SOC due to land use and management may be partly explained by the way C is allocated in these different SOC fractions (Tan et al. 2007). Previous research in the Loess Plateau of northern China indicate that, compared with the grassland restored from cropping, continuous tillage and proper management in cropland increased SOC storage in the lower soil horizons (Li et al. 2008). This study was conducted to investigate the distribution of light- and heavy fractions of SOC under cropland and grassland, aiming to better understand how the density fractions of SOC were affected by the land use conversion