MODELING AND PARAMETERS SENSITIVITY ANALYSIS OF NITROGEN LOSS THROUGH RUNOFF FROM UPLAND IN THE YANGTZE RIVER DOWNSTREAM

The excessive use of nitrogen fertilizer for crop production can cause substantial N losses through surface runoff. In this study, a simulation model was developed to describe the fate behavior of nitrogen loss through runoff in upland field in the Yangtze River downstream. The model was calibrated and validated using the rainfall events in this area from 2009 to 2010, in which the rainfall events in 2009 were used for calibration and the rainfall events in 2010 for validation. The performances of the model in validation period were well accepted with the Nash-Sutcliffe efficiency index above 0.98 and 0.75 while relative error below 10% and 15% for runoff loss and nitrogen loss, respectively. Sensitivity analysis of the model suggested that the precipitation and effective hydraulic conductivity were high sensitive factors for both runoff loss and nitrogen loss, while the effect of initial soil nitrogen concentration was just obvious on nitrogen loss. Furthermore, the effects of surface roughness, soil erosion index and vegetation coverage on the nitrogen loss were not obvious. The result of the study suggests that precipitation, fertilizing amount and soil texture are the main factors of nitrogen loss for upland field and other similar areas, which should be paid more attention on the farmland nitrogen loss prevention and control.