坝上地区土地利用与覆被变化对土壤养分的影响

Effect of Land Use and Land Cover on Soil Nutrients.

坝上地区是典型的农牧交错带 ,生态环境十分脆弱。研究表明 ,解放后 ,该区土地利用与土地覆被状况经历了多次反复的变动。 2 0世纪 80年代以前 ,草地大规模改变为旱地 ,部分改为林地 ;90年代初 ,旱地又逐步被改为草地、林地和水田使用。土地利用与土地覆被的变化引起土壤中有机质、全N、全P、全K、碱解N以及有效态P、K、B、Mo、Mn、Zn、Cu和Fe等养分呈有规律的改变。当土地由草地变为林地、旱地变为林地、旱地变为水田时 ,总体养分增多。但也有例外 ,尤其是碱解N、速效P和速效K以及微量元素 ,有时出现与上述规律不一致的情况。

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.