桂西北喀斯特移民区土地利用方式对土壤养分的影响

利用典型喀斯特峰丛洼地主要土地利用方式（灌草地、次生林地、果园、牧草地、旱地）的土壤养分测定数据，研究土地利用变化对土壤养分的影响.结果表明：土壤有机碳、全氮、有效氮含量随土地利用强度的增加而降低，灌草地和次生林地比果园、牧草地和旱地土壤有机质含量高86%～155%、全氮含量高62%～119%、有效氮含量高66%～215%（P<0.05）；全磷和全钾含量主要受养分来源的影响，受土地利用方式影响较小；速效磷含量主要受施肥的影响，有效钾含量则主要受植被覆盖和水土流失状况的影响.土地利用方式是影响土壤有机碳、全氮、有效氮、有效磷、有效钾等养分含量变化的重要因素.粗放的农业耕作降低了土壤养分并引起土壤退化，而植被恢复等措施可以培肥土壤.因此，喀斯特区域应改变粗放的农业耕作方式，加强施用有机肥和平衡施肥，对坡度≥25°的坡耕地采取“退耕还林还草”措施，以恢复和重建喀斯特地区生态环境，实现土地资源的可持续利用.

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.