关键词: 农田, 地表径流, 氮、磷流失, 丘陵地区, 典型灌区

Abstract: In order to reveal the mechanisms of agricultural non-point source pollution, the Zhanghe Irrigation District in Hubei Province, a typical irrigation district in hilly areas in central China, is selected to conduct field experiments on the influencing factors and characteristics of nitrogen and phosphorus losses in surface runoff from farmland. On the basis of field observation in Tuanlin Experiment Station in the irrigation district in May-September, 2007, the influencing factors and laws of nitrogen and phosphorus losses in surface runoff from paddy rice and corn fields are analyzed. In the experiment station, observations on 10 plots of three kinds of typical terrain are conducted for field-scale experiment. Observations include surface runoff and water leakage monitoring under different land-use types and different irrigation activities. Water sample analysis indicators in surface runoff from the fields include total nitrogen, nitrate-nitrogen, ammonium-nitrogen, total phosphorus and phosphate-phosphorus, and the chemical analyses are conducted according to the national standards. The results show that land-use types have a significant effect on the concentration of the nitrogen, and the total nitrogen losses in surface runoff are in the order of corn > paddy rice. Land-use types have greater impact on the losses of total phosphorus but not at a significant level. With the increase of rainfall intensity from 6.0 mm·d^-1 to 52 mm·d^-1, ammonium-nitrogen and nitrate-nitrogen concentration decreased remarkably, organic nitrogen increased from 3.2% to 69.7%, inorganic nitrogen decreased from 96.8% to 30.3%, which means that the proportion of organic nitrogen lost in the surface runoff increased; while the total phosphorus and phosphate-phosphorus concentrations increased gradually. Through using the water-saving irrigation technique, rainfall use efficiency was increased by about 14%~23%, irrigation water was saved up to 25%, and surface drainage was decreased by about 20~25 mm, thus, water pollution caused by the losses of nitrogen, phosphorus and other nutrients in surface runoff can be reduced effectively. Crop growing stages and topography and landscape also have impacts on rainfall-runoff characteristics and farmland nutrient losses.

Key words: farmland, surface runoff, nitrogen and phosphorus losses, hilly area, typical irrigation district