The impact of land use type changes on soil nutrinet in suburban area:the case of Daxing District in Beijing
城乡交错带土地利用变化对土壤养分的影响——以北京市大兴区为例

Land use changes can not only change land cover, but also influence a variety of natural phenomena and ecological processes, including soil conditions, water runoff, soil erosion and biodiversity. The rational land use can improve soil structure, strengthen resistance to the environmental change, and the irrational land use can lead to land degradation, such as water and soil loss, land desertification. Daxing District located to the south of Beijing, was taken as a case study for illustrating the effects of land use change on soil fertility. The 1:50,000 soil map produced in the Second National Soil Survey (SNSS) in 1982 was digitized with GIS supporting. Top soil samples were collected from the same soil sampling sites of the 1:50,000 soil map with GPS reference locations, from May to June 2000. Three samples collected around each sampling point were mixed and a quarter of each sample was kept for laboratory analysis. At the same time, farmers were interviewed for fertilizer input, irrigation, yield, land management, etc. The soil samples were air-dried and ground to pass 0. 15 to 1 mm sieves in the laboratory. Chemical properties of soils were analyzed using standard methods. The content of organic matter, total N, available N and available P increased by 31. 02%,50%, 37.89% and 177% respectively, but that of available K decreased at the same time. The order of content changes of organic matter, total N and, available P is different between different land use types in 1982 and 2000, which is horticulture land> water land>irrigable land>vegetable land>dryland>forest land. Due to the transition of water land into irrigable land, vegetable land and horticulture land, the order of changes of organic matter, total N and available N is dryland> horticulture land> irrigable land> vegetable land, the order of the available P is horticulture land>irrigable land> vegetable land >dryland, the available P increased in horticulture land and dryland, but decreased in vegetable land and irrigable land to some extent. The order of organic matter and the available P is horticulture land> irrigable land> dryland, that of total N is dryland> horticulture land>irrigable land, and the available N is irrigable land > horticulture land > dryland, with the dryland transiting into irrigable land and horticulture land. The extent of the available K decreased, but the other nutrients of soil increased at the same time when sandy wasteland were transited into such land types as irrigable land, horticulture land, dryland, forest land and vegetable land.