Study On The Loss Characters Of Nitrogen And Phosphorus From Sloping Farmland And Their Affecting Factors Under Corn-wheat Cropping System In Danjiangkou Reservoir Area

Agricultural non-point source (NPS) pollution refers to the transport and diffusion of agricultural chemicals, feces from livestock breeding and sewage, etc. from agricultural field ecosystem to water body by ways of runoff, drainage and leakage. Agricultural NPS pollution is mainly resulted by agricultural production and has been one of the important causes of water quality deterioration of receiving water body (including rivers, lakes, reservoirs and bays). The characteristics of Agricultural NPS pollution are wide range, low concentration and dispersed pollutant. In a worldwide scale, Agricultural NPS pollution is or has been the important cause of soil and water pollution. Danjiangkou reservoir, as the water source, plays an important role for ensuring the quality of water that transported by Middle Route of South to North Water Transfer project. Recently, the water quality of Danjiangkou reservoir tended to decrease, which was not only closely related to the fragile agricultural ecological environment and climate condition, but also related to relatively high rate of N (or N and P) fertilizers application.In this study, the present situation of agricultural NPS pollution in Danjiangkou reservoir area, fertilizers use status and the main problems in crop production in the studied area were made clear by sample investigation and analysis. And by field experiment, the loss and the affecting factors of nitrogen (N) and phosphorus (P) from sloping farmland under corn-wheat cropping system were studied, the corresponding countermeasures for controlling the loss of N and P from sloping farmland were also suggested. The main results were as follows:1) In Danjiangkou reservoir area, N and P loss from crop planting was the main factors for water body eutrophication, with the equivalent pollution load ratio of36.08%and21.71%, respectively in total agricultural NPS pollution load.2) In the studied area of Xiao fuling village, Xijiadian town, Danjiangkou city, over30%of the farmers applied relatively high rate of N fertilizers on corn with an average N rate of253.5kg/hm2, and over40%of the farmers applied relatively high rate of N fertilizers on rice with an average N rate of258.2kg/hm2, which was a hidden risk of environment pollution.3) In OPT treatment, the economic benefit was high than that in FP treatment because of high crop yield; in20%OM-N treatment, the economic benefit was high than that in FP treatment because of lower cost of Fertilizer; in2N+2P treatment, the economic benefit was lower than in any other treatments because of high cost of Fertilizer but lower crop yield.4) Under conditions of this research, different fertilization treatments had no significant effect on runoff from sloping farmland. The continuity of rainfall and the field capacity could effect on runoff and its coefficient; the runoff coefficient after multiple short alternation rainfalls was significant high than after long alternation rainfalls.5) The runoff of sand from sloping farmland effected by the runoff and the concentration of sand, decrease in any of them could get comparatively ideal effect on soil and water conservation.6) The concentration of N in runoff increased with increasing of N fertilizers application rate, and concentration of total N in runoff in OPT treatment was significantly lower than that in FP treatment, however, top-dressing time of N fertilizer should be conducted according to weather conditions, and rainy days should be avoided.7) The concentration of P in runoff tended to increase with increasing of P fertilizers application rate, but the trend is not very significant some time; in2N+2P treatment, the high P fertilizers application rate effected high concentration of P in runoff, and kept for a long time. When part of P was used with organic fertilizer instead of chemical fertilizer, the ratio of soluble organic P in runoff tended to increase, whereas the total P in runoff tended to decrease.8) Soluble N loss was the main in the total N loss, while the percentage of particulate N loss tended to increase with increasing of runoff and the sand concentration in runoff. Under conditions of this research, different fertilization treatments had no significant effect on phosphorus forms in runoff, the concentration of dissolved P and particulate P in runoff approximately quite, that showed the importance of the runoff of sand to the P.9) The total rainfall of corn season2010was431.5mm, the runoff coefficient was between6.78%and7.05%; the total rainfall of corn season2011was325.3mm, the runoff coefficient was between7.23%and8.04%, the runoff coefficient of corn season2011was significant high than corn season2010. That showed the effect on runoff from sloping farmland from weather, rainfall, soil moisture and the interval of rain.10) Under conditions of this research, different fertilization treatments had no significant effect on the concentration of NH4+-N in soil of20-40cm under the surface, but the concentration of NO3--N in soil of20-40cm under the surface significantly increased with increasing of N fertilizers application rate. 11) Optimized fertilization and part of organic fertilizers substitution were2relatively rational fertilization measures, which could decrease total N and P loss from sloping farmland by runoff. Together with other agronomic and engineering measures for soil and water conservation, N and P loss from sloping farmland by runoff could be greatly decreased, and finally to minimize the negative impact on the environment and the water quality of Danjiangkou reservoir.