关键词: 土地利用, 土地覆被, 变化, 土壤养分, 坝上地区

Abstract: Bashang region is a typical agriculture-pasture-interlacing zone,whose eco-environment is fairly vulnerable and hence it is very sensitive to environmental changes.Located only about 200 km away from Beijing and Tianjin,the region is a water-source and an ecological protection barrier for Beijing and Tianjin.Thus,study on the area is of great significance.Since 1950s,land use and land cover have undergone several changes.Before 1980s,large areas of grassland were turned into upland fields and some into woodland.And in early 1990s,the farmland was gradually changed back into grassland and some into woodland or paddy fields.The alteration of land use and land cover caused changes in soil nutrients,such as organic matter,total N,total P,total K,alkali-hydrolyzable N,and readily available K,readily available B,Mn,Zn,Cu,and Fe,though regularly.When grassland was turned into woodland or upland fields into woodland or paddy fields,total soil nutrients increased.This was only a general trend.Exceptions did exist,especially with alkali-hydrolyzable N,readily available P,readily available K,and micro-elements,which sometimes altered inconsistently with the above-said patterns. 

Key words: land use, land cover, change, soil nutrients, Bashang region