Research in soil nutrient content of sloping field of typical watershed in three gorges reservoir area

A small watershed in Zhongxian, Chongqing, was chosen to study the soil phosphorus content distribution in sloping field of different planting modes and assess the loss risk The results were as follows: (1) In 2009, the average content of total soil phosphorus, available phosphorus and water soluble phosphate were 0.54±0.18 g/kg , 32.14±32.63 mg/kg and 2.46±2.21 mg/kg. The total phosphorus content which was in different land in order from high to low as follows: fruitland, dryland, riparian land, grass land and paddy field; whereas the order of available phosphorus and water soluble phosphate content from high to low were as follows: fruitland, dryland, paddy field, grass land and riparian land. (2) The content of total soil phosphorus was positively correlated with the content of available phosphorus and soluble phosphate. The risk of desorption phosphorus flowing into water bodies increased with the addition of the content of total soil phosphorus. (3) The critical loss content of available phosphorus was 60.79 mg/kg. Up to 50% of the soil samples of fruitland exceeded critical loss value, having the highest loss risk; 6.7% of the soil samples of dryland exceeded critical loss value, having relative lower loss risk; the soil samples of riparian land, grass land and paddy field were lower than critical loss value, achieving the lowest loss risk.