Effects of hydrological factors on nitrogen loss in small agricultural catchments

Soil nitrogen loss processes resulted from rainfall and runoff were monitored in a small agricultural catchment of red soil areas in Jiangxi Province with the aim to investigate the relationship between the soil nitrogen loss and the corresponding rainfall and runoff.The results show that the concentration of NH~+_4-N and total nitrogen in the overland runoff is high in the beginning of rainfall and runoff,and then decreases rapidly with rainfall and runoff,the concentration of NO~-_3-N shows no appreciable change.Surface runoff have an important influence on the total nitrogen loss and subsurface runoff affect the nitrogen loss.The nitrogen loss mainly occurs in April to June.In the upstream dry field,losses about 74% of annual loss for NH~+_4-N,61% for NO~-_3-N and 62% for total nitrogen take place in this period.At the basin mouth,the relevant figures were 82%,70% and 79% respectively.The annual total nitrogen loss is up to 43.8kg/hm~2,which accounts for 22.6% of nitrogen fertilized by farmers.