Impacts Of N And P Accumulation In Soil Of Farmland On N And P Leaching Losses In Riverine Plain Area Of Taihu Lake

Non-point pollution from crop production was very serious in Taihu area,which led to lakes eutrophication,soil quality decline,rivers deteriorism and threaten the whole environment quality and resident health.There were many reasons that caused agricultural non-point pollution.Nitrogen and phosphorus leached losses from farmland soil were important reason.Jiaxing was situated in riverine plain area of Taihu Lake.Hypsography plainness,river net interveining,rainfall high frequency,paddy field and dry land rotate, mass nitrogen and phosphorus plough into farmland.The unique hydrography characteristic was the advantage on the nitrogen and phosphorus leaching losses.There was representative signification for study on nitrogen and phosphorus leaching losses in riverine plain area.In order to obtain the relationship between N,P accumulation in soil and the N,P concentration in leaching water in farms with different crops in Taihu Lake Watershed. From Jul.2006 through Sept.2007,a series of field trials were carried out by fixing pumping water equipments in farms in Jiaxing,Zhejiang Province.10 plots of 3 types were selected,water and soil samples were collected and analyzed.The results showed that:Nitrogen and phosphorus leaching losses from farmland was one of the important sources of Taihu Lake eutrophication,In order to control nitrogen and phosphorus leaching losses effectively,how nitrogen and phosphorus leaching lose from farmland should be studied firstly.Processes and characteristics of nitrogen and phosphorus leaching losses vary with not only precipitation but also site-specific characteristics,namely different factors of site-specific location,including crop types,cultivation systems,groundwater table,terrain,irrigation and drainage conditions,soil N,P concentrations and fertilization etc.And the differences of all these site-specific characteristics can result in significantly different nitrogen and phosphorus leaching losses way and characteristics.Nitrogen leaching loss characteristics in farms with different crops:The average content of pure nitrogen fertilizer was 1568.4Kg/(hm²Â·a) and 1634.6Kg/(hm²Â·a) in vegetable fields and orchards respectively,about 4 times as much as that of paddy plots.The most of nitrogen in the soils was accumulated in the profile of 0-5cm layer and the content of NO₃^--N was decreased gradually with the depth of soils.The content of NO₃^-N in 0-5cm soil layer was 201.7mg/kg in vegetable fields and 230.7mg/kg in orchards,which was more than 20 times as much as that of paddy plots.N accumulation in the soil was the main reason that caused N leaching in the farms.There was a significant positive relationship between NO₃^-N accumulation in soil layer and N concentration in leaching water,which indicated that the NO₃^--N leaching capacity increased gradually with the N accumulated in soil of farmland and it must increase N leaching loss risk.Phosphorus leaching loss characteristics in farms with different crops:The average content of pure nitrogen fertilizer was 946.8Kg/(hm²Â·a) and 832.6Kg/(hm²Â·a) in vegetable fields and orchards respectively,about 10 times as much as that of paddy plots.The most of phosphorus in the soils was accumulated in the profile of 0-5cm layer and the content of Olsen-P was decreased gradually with the depth of soils. The content of Olsen-P in 0-5cm soil layer was 161.8mg/kg in vegetable fields and 143.9mg/kg in orchards,which differ with significantly that of paddy plots.Ratio of Dissolvable Reactive Phosphorus(DRP) to Total Phosphorus(TP) was 37.6%-78.2%,most of that was higher than 50%.The content of P in leaching water in vegetable fields was much higher than that in orchards and paddy plots.P content in the soil was the main reason which caused P leaching in the farms.There was a significant exponential relationship between Olsen-P accumulation in soil layer and P concentration in leaching water, indicating that P concentration in leaching water increased steeply,when Olsen-P content exceeded some level.