Study On Nutrient Runoff Character Of Wheat-rice Double Cropping System Field In Meeting Place Of Hung-tse Lake And Huaihe Rive

Hung-tse Lake is the fourth largest freshwater lake in China.It is also one of the key hinge lakes in the east route of the south – to – north water transfer project.However,at present,the water quality has been reduced to the worse,which is one of the important reasons of non-point source pollution.Although,the agricultural non-point source pollution has raised some attention in the regions around Hung-tse Lake,compared with other large lakes such as Taihu,the current quantitative research about nitrogen and phosphorus loss in farmland in the regions of Hung-tse Lake is relatively scarce,and is not suitable for the development level of the Chinese lake ecological environment.To provide scientific basis for the effective control of runoff nitrogen and phosphorus loss and the prevention of eutrophication and groundwater pollution in Hung-tse Lake.The characteristics of nitrogen and phosphorus loss in wheat-rice double cropping system field were studied by field monitoring experiment under the conventional fertilization in meeting place of Hung-tse Lake and Huaihe Rive.In addition,the characteristics of fertilizer input and nutrient balance and groundwater quality were also evaluated in this paper.The main results were as follows:(1)The variation range of runoff coefficient of wheat and rice season were 0.32-0.63(the average was 0.45)and 0.22-0.51(the average was 0.41),respectively,in meeting place of Hung-tse Lake and Huaihe Rive.There was a significant linear correlation between 0-20 cm soil water content before rain and runoff coefficient.The relationship between rainfall(x)and runoff(y)during the growth of wheat and rice could be expressed by y = 0.5477x-1.802(r = 0.9855**),y = 1.0604x-4.44(r = 0.9971**),respectively.Therefore,it could be estimated that the minimum rainfall for runoff from wheat and rice season were 3.3 and 4.2 mm,respectively.There was a significant positive correlation between the content of ammonium nitrogen in soil and runoff in the wheat field,while the nutrient content of surface water and runoff were all significantly positively correlated in the rice field.(2)The total nitrogen and phosphorus runoff loss in the wheat-rice double cropping system field were 31.98 and 0.94 kg/hm2,respectively,in meeting place of Hung-tse Lake and Huaihe Rive.Among them,the total nitrogen and phosphorus runoff loss in wheat season accounted for the total loss were 50.2 and 5.3%,respectively;Also,in rice season were 49.8 and 94.7%,respectively.The loss of nitrogen and phosphorus in wheat season was dominated by nitrate and particulate phosphorus,respectively.But the corresponding in rice was dominated by ammonium nitrogen and dissolved phosphorus,respectively.Except for the nutrient of total phosphorus in wheat season,the rainfall were all positively correlated with other nutrient losses in wheat-rice double cropping system field.(3)In the current management of nitrogen and phosphorus in field,the surplus of phosphorus was the largest,and the surplus rates of wheat and rice season were 158.92 and 80.32%,respectively.The surplus of nitrogen was relatively small and the surplus rates of wheat and rice season were 41.76 and 21.97%,respectively,in the wheat-rice double cropping system field.Therefor,reducing fertilization could help reduce the loss of farm runoff nutrients.Under such conditions,the concentration of nitrate in groundwater was 0.79-5.05 mg/L(the average concentration was 1.78 mg/L),and the concentration of total phosphorus was 0.009-0.090 mg/L(the average concentration was 0.029 mg/L).It could be concluded that the groundwater quality belongs to high quality grade.This also indicated that the nutrient of nitrogen and phosphorus runoff loss in field had no significant effect on groundwater quality.