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Nitrogen Balance, Pollution and Management in a Typical Agro- Forest Ecosystem

PENG Kui1, OUYANG Hua1, ZHU Bo2, Erle C. Ellis3( 1. Institute of Geographical Sciences and Natural Resources Research, CAS, Beijing 100101, China; 2. Institute of Mountain Hazards and Environment, CAS, Chengdu 610041, China; 3. Department of Geography & Environmental Systems, University of Maryland, Baltimore, Maryland, USA)  
Field experiments; inspections and participatory rural appraisal were adapted to study on nitrogen balance and non- point source pollution in a typical agro- forestry ecosystem. The results showed that there was a little nitrogen surplus in croplands and in farming system; but a little deficit in paddies and in the catchments nowadays. In addition, the forest system showed more deficits. However, the recorder in 1960s showed a great N deficit mainly because of heavy erosion. The nitrogen balances of croplands and paddies were relatively reasonable by a mathematical appraisal model. Unfortunately, a great increase of N chemical fertilizer applications had already led to more non- point pollution risks of gas N emissions and - N concentration in water surface and groundwater. It has been clear that the forest was playing a great role in reducing erosion and improving the nitrogen distribution among different ecosystems. Logical fertilizer applications, forest protection, no- tillage farming and nutrient management policy were the important ways in reducing non- point resource pollutions of agricultural N.
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