Effects of vegetation types on yield of surface runoff and sediment, loss of nitrogen and phosphorus along loess slope land

Abstract: Vegetation types affect process of runoff, soil erosion and nutrient transport along loess slope land. In order to clarify the influence of vegetation types on surface runoff, sediment transport and nutrients in loess region, a field water scouring experiment was performed on a natural, fallowed loessial slope (38°46′-38°51′N, 110°21′-110°23′E) on 14 km west of Shenmu Erosion and Environment Research Station of Institute of Soil and Water Conservation, Chinese Academy of Sciences, in the Liudaogou watershed, Shenmu County, Shaanxi Province at Shenmu. A steady-head water scouring method was adopted under natural conditions. Field plots were established on a slope that had been fallowed for 7 years. Herbaceous and crops were selected as vegetation types, including maize, millet, soybean, cymbaria dahurica, alfalfa and caragana. Runoff, sediment, and nutrients (nitrogen and phosphorus) under different vegetation cover were determined. In addition, basic growth characteristics of various vegetations in each plot were measured. Results showed that compared with the other vegetations, the effect of herbaceous (cymbaria dahurica) on the decrease of surface runoff was largest, and soybean was the lowest. With vegetation cover, less sediment was carried with by runoff, the process of sediment appeared a peak for all the vegetation cover, and alfafa cover significantly decreased sediment loss. Under different vegetation covers, the concentration of nitrate nitrogen and soluble phosphorus in runoff water decreased rapidly at the initial runoff stage, and then to be stabilized. The process of nutrients (nitrate nitrogen and soluble phosphorus) transport could be better described with power function than exponential function. Results also revealed that the amount of nitrate nitrogen in sediment decreased rapidly, while the amount of effective phosphorus in soil reduced gradually over time. When soil surface was covered with alfalfa, and the total loss of nitrate nitrogen and phosphorus in sediment was highest. It could also be found that nutrients enrichment ratio had a reverse relationship with erosion amount for the all vegetation cover. The total loss of nitrate nitrogen under different vegetation cover was highest in millet cover, followed by alfalfa, caragana, maize, soybean, and cymbaria dahurica, and the total loss of soluble phosphorus was highest in millet cover, followed by maize, caragana, soybean, cymbaria dahurica and alfalfa. Nitrate nitrogen showed a peak feature along depth in soil profile, and the peak position was different for different vegetation covers. Phosphorus was mainly cumulated at the top 5 cm of the surface layer, and the amount of phosphorus was extremely low below 5-cm soil depth. In conclusion, the effects of herbaceous cover on surface runoff, sediment transport and the loss of nutrients were much better than crop cover. This study provides a way for further analyzing the effect of vegetation cover on water and soil nutrient loss, and provides a guide for controlling soil water loss and agricultural management.