Soil erosion and nutrient loss due to erosion are world-wide problems. Similar to soil loss byerosion, soil nitrogen (N)
loss by erosion in small catchments is affected by
vegetation coverage. Thepractice of comprehensive management for catchments mainly by adjusting cropland, grassland and wood-land areas was widely adopted to reduce soil and water loss in catchments of the Chinese Loess Plateau.Three experiments under natural and artificial rainfall conditions on N loss by erosion for a model catch-ment and for an actual catchment in Zhifanggou of Ansai County in China was performed to determine therelationships between comprehensive management and N loss by runoff in small catchments. The resultsfor
Vegetation coverage of 60%, 40%, 20% and 0 show that runoff loss of ammonium, nitrate, and total Nwere 87.08, 44.31, 25.16, 13.71 kg/km2; 85.50, 74.06, 63.95, 56.23 kg/km2; and 0.18, 1.18, 1.98, 7.51 t/km2, respectively. Due to reduction in the size of cropped area on steeply sloping land, soil N loss byerosion in the catchments was decreased by 15.8% as compared with that in 1992, i.e., from 8 758.5 kg in1992 to 7 562.2 kg in 1998. Whereas, catchments act as a filter for ammonium and nitrate in rain, thecatchment filtering effects on nitrate is remarkably higher than that on ammonium. The enrichment of <20 mm aggregate in sediment results in the enrichment of organic matter and total N in flood sediment.Greater vegetation coverage can effectively decrease soil erosion and total N loss. However, soil mineralN loss increased as vegetation coverage increased.