Nitrogen leaching from catchments in the Middle Hills of Nepal; an application of the INCA model

Application of a semi-distributed integrated nitrogen model (INCA) to forested and cultivated catchments of the Middle Hills, Nepal is described. The model simulations have determined the fate and distribution of multiple sources of nitrogen including atmospheric inputs and fertiliser applications to terraced agriculture. Predicted stream NH4-N and NO3-N concentrations broadly reproduce the low observed concentrations but discrepancies are evident which probably arise due to the variability in both rainfall N concentrations and land management practices. The impact of predicted future increases in N input to catchments throughout this region is assessed. Stream N concentrations are predicted to increase. However, the predominance of gaseous loss of N from terraced agriculture is likely to ensure that future concentrations remain relatively low.