[Effects of different land use types on soil nutrients in karst region of Northwest Guangxi].

Selecting the main land use types (shrub land, secondary forest land, orchard, pasture land, and upland) at the peak-cluster depression in karst region of Northwest Guangxi as test objects, this paper studied the effects of different land use types on soil nutrients. The results showed that, the contents of soil organic matter (SOM), total N, and available N were 86%-155%, 62% -119%, and 66%-215% higher in shrub land and secondary forest land than in orchard, pasture land, and upland, respectively, i. e., increased with the decrease of land use intensity. The contents of soil total P and K were mainly controlled by their origins, but less affected by land use type. Soil available P content was mainly affected by fertilization, while soil available K content was controlled by vegetation cover and water- and soil loss. Land use type was the dominant factor affecting the contents of soil SOM, total N, and available N, P and K. Extensive cultivation could decrease soil nutrient contents and lead to the degradation of cropland soil, while ecological restoration could improve soil fertility. Therefore, in karst region, the measures as changing extensive cultivation into intensive farming, applying organic fertilizers, balance fertilization, and "Grain for Green Project" for > or = 25 degrees slope should be taken to recover and rebuild the eco-environment, and keep the sustainable utilization of land resources.