Technologies For Controlling Agricultural Non-point Source Pollution Of Chinese Chive Field In The North Bank Of Dianchi Lake

Pollution from agricultural non-point sources in Dianchi Lake valley is one of important reasons causing eutrophication of Dianchi Lake.It is significative to study and control the pollution in order to control eutrophication of Dianchi Lake.N and P losses from vegetable fields are major non-point source pollution because of high multi-cropping index of vegetable and high rates of fertilizer application.Field trils,cultural experiments combined with field investigation were conducted to study the agricultural non-pointed sources from the yellow Chinese chive production system on north bank of Dianchi Lake from August 2006 to April 2008.The technologies for controlling the pollution were developed on the basis of the current study.The main results are as follows:1.Losses of nitrogen and phosphorus due to excessive application of chemical fertilizer are one of major sources resulting in non-point sources pollution of agriculture.The treatment of decrease of N by 20%reduced amount of cumulative NH₃ volatilization by 34.2%～36.9% in one fertilizing period;decrease of the total nitrogen content of leaching,lateral leaching and runoff by 37.0%,22.2%and 28.9%were observed。The soils in the study area are alkaline. The pH of soils reduced obviously three months after application of sulfur,which resulted in obvious decrease of ammonia volatilization.The cumulative NH₃ volatilization due to sulphur application reduced by 59.6%～65.5%compared to without sulfur treatment,and the yields of yellow Chinese chive increased by 12%～15%due to sulfur fertilization.The application of DCD significantly inhabited nitrification of soil NH₄⁺,obviously increased content of soil NH₄⁺,and significantly decreased content of total nitrogen in leaching and lateral leaching. The application of DCD also increased yields of Yellow Chinese Chive by 8.7%～12.4%,but reduced content of nitrate in Yellow Chinese Chive by 24.8%.Therefore,the measures of decreasing nitrogenous fertilizer combined application of sulfur and DCD could reduce N losses from field,and increase yields of Yellow Chinese Chive and reduce its nitrate content.2.The Chinese Chive discarded in the process of growing Yellow Chinese Chive were usually thrown away into water body of ditch,then these were decomposed in situ.The method mentioned above is one popular method managing the agricultural organic waste material.Decomposing of the waste material is also another mainly resource of agricultural non-point sources pollution.Total 60 water samples of ditch were collected and N and P etc were also analyzed.The content of TN in the water with situ decomposed Chinese Chive was as 15.5 times as that in the water without Chinese Chive,the corresponding values for NO₃^--N,NH₄⁺-N,TP,COD was 4.4,24.1,5.5,8.3 respectively.The above-mentioned results implied that the decomposed Chinese Chive seriously polluted the water of ditch.The result of cultivation experiment indicated that the content of TN,NO₃^--N,NH₄⁺-N,TP,H₂PO₄^2--P,COD_Crincreased as the time of Chinese Chive's decomposing went on.The contents of TN,NO₃^--N,NH₄⁺-N reached the peak on the 12th day of decomposing, subsequently decreased slowly.The content of P(TP,H₂PO₄^2--P)reached the peak on the 6th day,and COD_Cron the 15th day.The decomposed Chinese chive in water resulted in a obviously decrease of water pH.All the Azolla imbricate died on the 12th day of decomposing,and Lemna minor were discovered traces of poison at the same time.60%of Lemna minor also died on the 15th day.High content of NH₄⁺-N was the major mechanism causing Lemna minor and Azolla imbricate's poisoning.Therefore,the discarded Chinese Chive's decomposing in situ not only contaminated the water,but also affected the growth of hydrophytes,and then affected the capacity of water's self-purification.Developing the technologies of Chinese chive resource utilization should have a practical significance on control the non-point source pollution resulting from Chinese Chive production.3.Lemna minor and Azolla imbricate can be used to effectively purify non-point source polluted water.These plants can grow well on water containing TN 6.91～50.87 mg·L^-1or TP 0.63～6.11 mg·L^-1,and have a high ability of resorting N and P.The results of field trial indicated Lemna minor reduced TN by 28.0%～46.8%and TP by 48.7%～83.6%;Azolla imbricate reduced TN by 37.5%～57.7%and TP by 60.8%～89.4%compared to water without plants.Plants could be returned to farm as green manure,which can enforce recycling utilization of nutrients.To sum up,a suit of technologies were put forward to control agriculturial non-point source pollution in the study area.Firstly,it is necessary to reduce waste material discarded into ditch and reduce the rates of nitrogenous fertilizer in order to control the pollution from headstream.Secondly,sulfur and DCD could be applied to vegetable fields to reduce ammonia volatilization and nitrogen loss from leaching and lateral leaching.Thirdly,Lemna minor or Azolla imbricate could be used to purify the polluted water in dich,subsequently these could be returned to farmland as green manure.The suitability,easy operation and low cost of these techniques developed in the present study are prone to be extensively applied in the study area.