The Risk Evalution Of Soil Phosphorus Loss In Yujia River Catchment Of Northern Qinling Mountains

Agriculture had become an important source of non-point source pollution, andphosphorus was the key factor of agricultural non-point source pollution. Phosphorus lossunder two kinds of land use, kiwi-fruit orchard and arable land, and river phosphorus changein the Yujia river catchment of northern Qiling Mountains were studied. The samples includedsurface layer(0~20cm)samples of43kiwi orchard and28arable land and three profile(0~100cm)samples of two types of land use. Characteristic of soil adsorb phosphorus and losspotential were Compared under two kinds of land use, analyzed fertility and leaching risk ofsoil phosphorus. Collected river sampling on eight points followed river flowed every monthafter rainfall, five forms water phosphorus were assayed. Here were some conclusions.1Soil maximum absorption of phosphorus and phosphorus sorption index weredecreasing under the condition of fertilizer applying, the maximum buffer capacity could notgreatly changed, with little difference between two kinds of land use. Applying manure couldsignificantly improve degree of phosphorus saturation (DPS) in kiwi orchard, increased therisk of phosphorus leaching. The results of prediction for eutrophication risk index was62.79%of kiwi orchard had higher risk for eutrophication, and96.43%of arable land was inlow risk.2The fertility was better in kiwi orchard than in arable land. The average of TP wascloseded to No.1class in kiwi orchard,60.46%was above No.2level, the average of Olsen-Pwas sufficient, with42.63%contain sufficient Olsen-P. The average of TP was in No.3classin arable land, its fertility mainly belonged to No.3or4class. The average of Olsen-P was inNo.4class, and96.43%being P deficient. Both the content of total P and Olsen-P showed thatthe surface layer was higher than bottom soil under two kinds of land use.3The change-point of phosphorus leaching by CaCl2-P and Olsen-P was40.11mg/kg forOlsen-P,62.79%of the orchard had possibility of phosphorus leaching. There was notobvious change-point for arable land, implying weak phosphorus leaching under decades ofcultivation. Here was a contradiction between high yield and phosphorus loss.The correlationbetween DPS and Olsen-P was obvious. The change-point for DPS was4.51%,58.14%ofkiwi orchard DPS was greater than4.51%with phosphorus loss. Soil DPS maximum was2.31%, the risk of P loss was low. Three predicting results was near. 4It showed seasonal law for the content of TP, TDP, PP, DRP in Yujia river. Differentfour forms of phosphorus content was higher from March to September than from Septemberto November, it was the lowest in November. The average was more than the critical value TP0.02mg/L from March to September, PP was the main form of phosphorus in river, withsimilar tendency of TP and accounts for around50%of TP. Content of DRP was low, andcontent of DOP mainly depended on the quality of the water itself.