Abstract: The mechanisms of nitrogen(N) losses through runoff (both overland flow and interflow) represent a significant portion of the N  biogeochemical cycle have been well documented for purple soil in the Sichuan Basin. It is unclear, however, how nitrogenloss takes place in agricultural slop land in the zone of fluctuating water level in the Three Gorges reservoir region. Nutrient loss may be increased and bring a great impact on the water environment of the Three Gorges Reservoir area while slope lands in the water level fluctuation zone used by local farmers spontaneously. Nitrogenloss through runoff in hill slope cropland in the water level fluctuation zone is unclear without any in situ monitoring. In this paper, we presented an in situ monitoring study of nitrogen losing forms, contents and fluxes via different pathways from slope land used for farming in the in the water level fluctuation zone during drawdown period through 2011 to 2013. The results showed that soil erosion modulus of slope land used for farming would be 1 443 kg·hm-2·a-1，while average annual runoff is 229.7 mm with interflow accounting for 77% of the total runoff discharge. The average total nitrogen in water of overland flow and interflow was 4.85±0.85 mg·L-1,20.73±2.05 mg·L-1，respectively. The annual total nitrogen loss via overland flow and interflow was 6.63±1.19 and 35.22±3.38 kg·hm-2，respectively, accounting for 2.2% and 11.7% of applied N fertilizer. Nitrate loss via interflow is the dominant route of nitrogen loss from the slope cropland. Compared with conventional fertilization rate, the loadings of total nitrogen were significantly reduced by 25% and 48%, respectively, in the overland flow and interflow under N-reduction fertilization. This indicates that reducing nitrogen application rate may decrease significantly the environmental risk of N loss from the slope land used for farming in the water level fluctuation zone. The intensity of nitrogen loss on slope land cannot be neglected while the slope land for farming of water level fluctuating zone, which may have potential risk of water pollution in the reservoir area. Therefore, restoration the ecological barrier function of water level fluctuating zone plays an important role in protecting the water environment of the Three Gorges reservoir area, suggesting the measures of reducing nitrogen application rate.
Key words：Three Gorges Reservoir; water level fluctuation zone; overland flow; interflow; nitrogen loading; reducing fertilizer application