Effect of land use on soil degradation in alpine grassland soil, China

Grassland soils in Northern China are being seriously degraded under cultivation and grazing. This study investigated the impacts of land use on soil erosion and soil fertility in alpine grassland of China. Land uses included three levels of pasture degradation, lightly (LDP), moderately, (MDP), and heavily degraded pasture (HDP) classified based on vegetation cover, and cultivated fields ranging from I to 50 yr of cultivation. Soil samples were collected from 18 sites at seven locations in Chernozemic soils between elevations of 2600 to 3000 m. Soil erosion was estimated by Cs-137 radioactivity. When pasture was heavily degraded, Cs-137 activity was significantly reduced, and organic C (OC), total N, and cation-exchange capacity declined by 33, 28, and 18% respectively. Cultivation of grassland worsened soil erosion, and after 8-, 16-, and 41-yr cultivation soil OC decreased by 25, 39, and 55%, respectively. Regionally, 59% of OC was lost within 30 to 50 yr of cultivation. There were concomitant losses of total N and exchange capacity. On cultivated soils, soil erosion and mineralization were equally responsible for organic C losses. Pasture degradation and cultivation also caused changes in soil P. Mineralization of organic P, incorporation of subsoil by tillage following erosion, and fertilization increased levels of Ca-P in cultivated fields. This study indicated that grassland degradation and cultivation caused not only, severe soil erosion, but also fertility decline and chemical changes of P dynamics.