Study On The Influence Factors And Environmental Risk Of Soil Phosphorus Loss In The Suburbs Of Wuhan

Suburb lies between inner city and typical agricultural region,and it is the transition zone with dual characteristics of city and countryside.With advancement of rural urbanization,suburb has already become the growing and supplying area of vegetables,fruits,flowers,etc.In surburb area,the condition of soil phosphorus accumulation and loss is becoming more and more serious with the intensity of plant and the degree of intensification being increased considerably.There are so many lakes in Wuhan and eutrophication in the some lakes is rather serious.The controlling of phosphorus that has been one of the key factors leading to the eutrophication of water is certainly worthy of more attention.The soils in the suburbs of Wuhan were studied by field sample analysis and laboratory simulation experiment to investigate the soil phosphorus characteristics from different land utilization,discuss the influencing factor of the soil phosphorus releasing and analyze the loss risk.Main results were summarized as follows:(1)The content extent of total phosphorus(TP),available phosphorus(Olsen-P) and bioavailable phosphorus(NaOH-P) in soil was rather huge.The content of TP was 255.4～1763.1mg/kg,and the average value was 975.4mg/kg.The content of Olsen-P was 1.3-164.2mg/kg,and the average value was 56.4mg/kg.And the content of NaOH-P was 33.4-910.7mg/kg,and the average value was 204.1mg/kg.(2)There was significantly correlation between the content of soil phosphorus and land use types.As to various lands use type,the order of different soil phosphorus content is as following in turn:vegetable soil＞paddy field＞the other dry lands＞nursery.The content of phosphorus in vegetable soil was higher than others and the its loss risk was higher than others obiviously.(3)Phosphorus sorption maximum(Qm) of vegetable soil was 138.9～476.2 mg/kg,and the average value was 336.5mg/kg.The degree of phosphorus sorption saturation(DPS) was 9.5%～109.3%,and the average value was 37.8%.The equilibrium phosphorus concentration at zero sorption(EPC₀) was 0.90～3.84mg/L, and the average value wasl.88mg/L.Qm of vegetable soil in Jiangxia was less than other areas.But its DPS was larger than others.So soil phosphorus adsorption capacity in Jiangxia was greatest and phosphorus fixing was lowest in all soil samples.(4)The different condition affected soil phosphorus to release,such as the initial phosphorus level,depth and time of overlying water.The higher initial level of soil phosphorus,the higher phosphorus released.In the initial stage of overlying water, solution concentration of phosphorus increased with the increase of overlying water depth.And from the initial day to the third day,the quantity of the soil phosphorus released was 90%～95%of the total released quantity.Soil moisture has insignificant influence on Olsen-P varation.(5)According to the Olsen-P grade separation levels,namely,low(＜10mg/kg), middle(10～20mg/kg),higher(20～40mg/kg) and highest(＞40mg/kg),there were 51.2%soil samples belonging to high risk level.Moreover,the content of Olsen-P was 56.0mg/kg was critical value and the content of Olsen-P from 34.9%soil samples exceeded 56.0mg/kg.Besides,the 15%level was the critical value of DPS to be used to evaluate the loss,and there were 44.4%exceeding 15%based on nine soil samples that had been analyzed.