Soil phosphorus balance in citrus orchards of three gorges area in Chongqing

Based on the data collection through farmer interviewing and agricultural statistics database, the characteristics of P fertlizaion and surplus were studied in Three Gorges area in Chongqing city. The result shows that the average application rate was P 228.8 kg/ha, with a main source of compound fertilizers and Calcium superphosphate; . The input rate through manure application was P 32.7 kg/ha，with a main source of animal waste and manures. Surplus in the orchards of the Orange, Jinchen were relatively higher than other orchards. The average P surplus is 107.6 kg/ha. Positive correlation was found between P surplus and applied P rate in orchards. Excessive P fertilizer input led to the increase of P surplus. Further, with the increase of phosphorus surplus, soil available phosphorus of orchard soil tends to increase, High P input in the orchards of some regions led to very high rate of P load to soil environment. Soil envrironmental P load in these orchards of the Orange and Jinchen were higher than the other orchards of three gorges area in Chongqing. Very high rate of P load in orchards will probably led to very hight soil and water environmental risk in three goges area.