Study On Nitrogen And Phosphorus Leaching Features On Soil Of Farmland In Small Basin

Soil is a nutrient storeroom where energy changes and material flows with a lot of physical, chemical and biological reaction. Soil nitrogen and phosphorus have many behaviors such as leaching to the water environment, which causes a strong effect on it. Leaching losses of nitrogen and phosphorus is not only the contribution to pollution of underground water and to eutrophication of water, but also the key composition of Non-point pollution. Because many factors, such as rain, fertilizer and so on, affect the behaviors of Leaching losses of nitrogen and phosphorus, its mechanism is pretty complicated. It is to choose the soil in the small basin of.Qiao Xiali country around Poyang Lake as the study object, study on the Leaching Features and put forward a useful controlling measures, whose aim is not only to bring forward some scientific date for manage underwater in the small basin and non-point pollution of Poyang lake, but also to protect the similar water environment, fertilization management and so on for their healthy development.Viaing controlling two arrangements of rain and fertilization intensions, it was to carry out four times experiments, and the results were as follows:(1)The water seepage in soil reflected the ability of moving. If soil moisture moved easily, the pollutants in soil affected the underground water more strongly. When the rain intension were 0.15,0.33,0.66mm/min, the amount of water seepage, respectively, got bigger, the ratio of water seepage got smaller, and kept at 10-30%, and the average was about 17.12%. As the soil in the experiment was terrene, the water seepage was small.(2)The rain had a distinct influence on leaching of nitrogen and phosphors in soil. Firstly, as the amount of rain got bigger, the ability of adsorption for NH4+-N was got stronger, but weaker for NO3-N. As the rain intension got stronger, the concentration of TN and NO3--N leaching leakage got more, but smaller for NH4+-N. Secondly, phosphors element mobility in the soil was poor, less affected by water. Vertical migration of phosphorus in the soil was not simply migrate from top to bottom, but with more complex forms of reaction such as adsorption, desorption and transformation, which leading to sustained periods of rainfall in this experiment, not enough to show the leaching features of TP. Thirdly, the rainfall intensity was constant, with the rainfall time increased, the concentrations of TN, NO3--N, NH4+-N and TP in leaching leakage decreased. Extension of time of rainfall, these indicators would maintain a relatively stable concentration and the emergence of smearing. For the nonfertilization of the soil, the rainfall intensity was at 0.66mm/min, the concentrations of TN, NO3--N, NH4+-N and TP became stable, at 70.0,25.0,1.0,0.14 mg/L, respectively.(3)There were certain correlations between leaching leakage (y,10-3 mg) and cumulative rainfall (x, mm) could be used to describe as natural logarithm. The following regressions were:TN y=59657.0Ln (x)-261132.0; NO3--N y= 4259.1Ln (x)-16887.0; TP y= 100.1Ln (x)-405.6, and all correlations were more than 0.98.(4)The fertilization also had a distinct influence on leaching of nitrogen and phosphors in soil. Soil fertilization was a source of nutrient leaching, and higher fertilization could induce much more intensity of nutrient leaching. The concentrations of TN, NO3--N, NH4+-N and TP in leaching leakage were in order of fertilization intensity N3 (460 kg/hm2)> fertilization intensity N2 (345 kg/hm2)> fertilization intensity N1 (230 kg/hm2). As the soil surface of the high nitrogen content (greater than 1.2g/kg), it resulted in: Cumulative fertilizer for 2 times(N1= 230 kg/hm2 and N2= 345 kg/hm2) also leaching for 3 times, the degree of soil TN leaching was the same to degree of leaching of fertilizer for the first time; cumulative fertilizer for 1 time (N1= 230 kg/hm2) also leaching for 2 times, soil NH4+-N leaching was weaker than the one without fertilization for the first leaching.(5)For the 4 fertilization intensity, the concentration relations of TN, NO3--N, NH4+-N and TP in leaching, were TP< NH4+-N< NO3--N<TN. For the blank soil leaching, the leaching leakage was mainly NO3--N and its ratio to TN was 68-80%. After urea fertilization, the main leaching leakage was not NH4+-N or NO3-N, respectively, about 30% to TN. Studies suggested that: nitrogen element in the form of leaching leakage was mainly NO3--N. This difference occurred, nitrogen element may be in the mainly form of amide nitrogen in leaching leakage. Because the transformation of urea in soil was slow, and rainfall duration was not long (about 10 hours), most of the urea hydrolysis was not able to hydro lyzed, and infiltration flowed too late, resulting in leakage of fluid may be mainly dominated by amide nitrogen.(6) There was strong linear regression relationships between intensity of fertilization and leaching. When the rainfall intensity was maximum, regressions between leaching intensity (y, kg/hm2) and fertilizer intensity (x, kg/hm2) for TN, N03--N and NH4+-N were ideal, and the correlation coefficients were above 0.99:TN y=0.1747x-26.1250; N03--N y=0.0142x+0.0530; NH4+-N y= 0.0051x-0.8583.(7)In order to realize the abatement of leaching of nitrogen and phosphorus in the small basin, and to cut down the risk to groundwater pollution and point source pollution, there were some useful measures about rainfall and fertilizer, as follows: reduce fertilization intensity, select the appropriate fertilization time, optimize the fertilizer mixture ratio and optimize the field drainage network.