Characteristics of Nutrient Transportation of Subsurface Flow of Purple Soil Slope

As one of the important runoff producing forms in purple soil area,nutrient loss by subsurface flow was always ignored.Taken the purple soil group as the research object,which is widely distributed on the slope-land in Three Gorges reservoir region,a series of simulated rainfall experiments under the different slope gradients(5°,10°,15°,20°)and the different rainfall intensity(0.6,1.1,1.6,2.12,2.54 mm/min),were conducted on the runoff plot which is 3.0 meters long and 1.0 meters width.The Characteristics of nutrient transportation of subsurface flow of purple soil was discussed.The results show that the percentage of the subsurface runoff account for 0.2%~2.7% in total runoff.There exists critical slope gradient and critical rainfall intensity,critical slope gradient is about 10° and critical rainfall intensity is about 2.1 mm/min.Nutrient concentration of subsurface flow is higher 4.32~63 times than that of the surface runoff.So,although the percentage of subsurface flow account for total runoff is not high,subsurface flow carried the nutrient is also can not be neglected.Total Nitrogen carried by subsurface flow account for 0.36%~7.82%of the total nitrogen loss from slope.So,we should not only controlled the surface flow generation,but also should improve the soil holding water capacity,decrease the amount of subsurface flow,if we want to restrict the nitrogen loss in purple soil area,phosphorus loss is related to the soil loss,phosphorus concentration in surface flow and subsurface flow are very low,so,phosphorus loss by surface flow and the subsurface flow is very limited,amount of the phosphorus loss carried by surface flow and the subsurface flow accounts for the total phosphorus loss is lower 7%,even lower than 1%.The key method of controlling phosphorus loss is to decrease the sediment yielding.