Soil organic carbon losses due to land use change in a semiarid grassland

Background and Aims Knowledge about the effect of land use change on soil organic carbon (OC) in semiarid grassland is essential for understanding C cycles and for forecasting ecosystem C sequestration. Our objectives were (1) to study the effect of land use change on aggregate size distribution, aggregate-associated OC concentrations, and aggregate-associated stocks in a semiarid grassland area and (2) to relate changes in the aggregate fractions to changes in total soil OC. Methods Cropland and shrubland plots were established in a semiarid grassland area in 1982. We collected soil samples from adjacent grassland, cropland, and shrubland plots 27 years later and measured OC concentrations in the macroaggregate (>0.25 mm), microaggregate (0.25–0.053 mm) and silt+clay (