Studies on soil nutrient redistribution under contour hedgerow system

Contour hedgerow system has been regarded as the most favorable agroforestry systems for water and soil conservation．However，it is more concerned whether hedgerows in the system compete with crops for belowground resources．especially nutrient beyond their crown areas．The nutrients in soil profiles in the system were analyzed for determining nutrients competition between hedgerows and crops in the system and nutrients redistribution pattern in the system．Organic matter and total nitrogen contents of topsoil(0～40cm)at different positions in hedgerow system are increased 1．2～ 2．3 times and 0．5～ 1．7 times over those of control respectively，and available P and exchangeable K have also increa sed remarkably after five years of hedgerow establishment，suggesting that contour hedgerow system is very effective for topsoil nutrient improvement．In hedgerow system．soil nutrients of 0～ 20 cm benea th hedgerow are higher than those beneath alley，therefore competition for nutrient doesn’t occur between hedgerow and crops．The results also show that nutrients status in alley varies with positions，namely，nutrients in downside alley are better than those in the middle and upper alley，and upper alley is the poorest position in alley．Available P and exchangeable K below 40cm beneath hedgerow was lower than those beneath alley，suggesting that root system of hedgerow is functioned as“nutrient pump” to uptake K and P from deep soil beyond crop root system and return them to topsoil by pruning of hedgerow．