Soil Nutrients of Degraded Wetland and Farmland in Sanjiang Plain

Reclamation of the Sanjiang Plain for development of agriculture has led to decline of the surface water table and soil moisture,thus triggering degradation of primary marshes into swampy meadow,or typical meadow,or even directly into paddy field and dry farmland.A study was carried out to compare degraded wetlands with farmland in nutrient content in the surface soil 0-30 cm deep.Four types of degraded wetland showed a sequence of paddy field>swampy meadow>dry farmland>meadow in terms of organic matter and total N;and paddy field>dry farmland>swampy meadow>meadow in terms of readily available P.It is clearly indicated that soil nutrients dropped significantly with primary marsh degrading into meadow,and that variation of the moisture regime was the most important factor leading to decline of soil nutrients.Soil nutrients of farmlands remained quite high,because of cultivation and fertilizer application. Therefore,change in moisture regime and human disturbances are the two important factors responsible for difference between degraded wetlands and farmlands in soil nutrient content.