Characteristics Of Nitrogen And Phosphorus Runoff Losses From Different Farmlands In Dianchi Watershed

Nitrogen and phosphorus runoff losses from farmland is the main source of Dianchi Lake eutrophication, to understand the characteristics and processes of nitrogen and phosphorus runoff losses from farmland is the precondition of estimating load of nitrogen and phosphorus and controlling nitrogen and phosphorus runoff loss from farmland accurately. Processes and characteristics of nitrogen and phosphorus losses vary is affected not only precipitation but also crop types,cultivation systems,soil nitrogen and phosphorus concentrations and fertilization ect. In order to understand the characteristics of nitrogen and phosphorus losses from different farmlands in Dianchi watershed,15representative farmlands were selected as monitoring site-specific locations in Dianchi watershed.These farmlands represent5main types:opening field vegetables, facility vegetable, facility flower, fruit trees, facilities combined opening field.By combination the method of continuous site-specific sampling and monitoring and artificial rainfall simulation, we have monitored different farmlands of nitrogen and phosphorus runoff loss in the rainy season(June-October2012), we have also studied the effect of fertilization and rainfall intensity on the processes and characteristics of nitrogen and phosphorus runoff losses from two typical farmland(opening field and facilities greenhouse) under simulated rainfall.The main conclusions are as follows:(1) The characteristics of runoff loss from farmland under simulated rainfall were:The two typical farmland of opening field and facilities greenhouse initial runoff-yielding time was exponentially decreasing with the rain intensity increasing. After the start of producing runoff the two typical farmland runoff yield at first increased and then tended to be stable. Under the rainfall intensity of40,80,120mm/h, rainfall runoff duration in60minutes, the opening field initial runoff-yielding time respectively was25.21,19.54,12.58minutes, the average effluent rate were0.44.0.70,1.23L/min; the facilities greenhouse initial runoff-yielding time was17.00,9.68,6.85minutes, the average effluent rate were0.76,1.42,1.67L/min. There were significant differences in initial runoff-yielding time and effluent rate when two types of farmland in the same rain intensity. The runoff of facilities greenhouse approximately were1.7,2.0,1.4times more than opening field.(2) The characteristics of nitrogen runoff loss from farmland under nutral rainfall were:Higher degree of variation during the monitoring period of each form of nitrogen loss, the coefficient of variation was59.87-178.57%. In addition to fruit trees farmland, the dissolved nitrogen was the main loss forms of the remaining4types of farmlands, the average occupies60.08%of the total loss consistence, while the particulate nitrogen was the main loss forms of fruit trees farmland, the average occupies73.42%of the total loss consistence. The size of load loss of nitrogen in different types of farmland basically was:facilities combined open field vegetables> opening field vegetables> facility vegetable> facility flower> fruit trees.(3) The characteristics of phosphorus runoff loss from farmland under nutral rainfall were:The degree of variation of each form of phosphorus loss was lower than nitrogen during the monitoring period, the coefficient of variation was47.83-118.13%. Particulate phosphorus was the main loss forms, the average occupies95.82%of the total loss consistence. The size of load loss of phosphorus in different types of farmland basically was:facility vegetables> facilities combined open field vegetables> opening field vegetables> fruit trees> facility flower.(4) Rainfall intensity, fertilization and soil nitrogen and phosphorus concentrations affects nitrogen and phosphorus runoff loss directly. With the increasing of rainfall intensity, the two typical farmland nitrogen and phosphorus runoff loss and loss load were increased with the increase of concentration. In the low rainfall intensity, risk loss of phosphorus of opening field was higher than facilities greenhouse. In the high rainfall intensity, risk loss of phosphorus of facilities greenhouse was higher than opening field. With the increasing of fertilization, various forms of nitrogen and phosphorus loss and loss load were increased with the increase of concentration. Interaction of rainfall and the amount of fertilizer has a significant impact on the total nitrogen, dissolved nitrogen, particulate phosphorus loss load. There were significant positive correlation between the average content of total phosphorus in surface soil0-20cm and runoff total phosphorus, dissolved phosphorus, particulate phosphorus.