植被类型对黄土坡地产流产沙及氮磷流失的影响

植被类型影响黄土坡地径流、土壤侵蚀和和养分迁移过程。该研究通过野外水流冲刷试验,对比分析了6种植被条件下坡面产流产沙及氮磷流失特征。研究结果表明,大黄花拦蓄径流作用最为明显,而大豆最弱;产沙量随时间的变化会出现峰值特征,其中苜蓿控制土壤侵蚀作用要优于其他植被;径流中硝态氮和水溶性磷的浓度在放水初期随时间迅速衰减,而后趋于稳定,幂函数比指数函数能更好的描述径流中硝态氮和水溶性磷浓度变化过程;泥沙中的硝态氮含量随时间迅速衰减,而有效磷的含量则随着时间逐渐波动减小,二者的最高含量均发生在苜蓿地。养分的富集率与土壤侵蚀量成反比;径流硝态氮流失总量的大小关系为谷子苜蓿柠条玉米大豆大黄花,水溶性磷流失总量的大小关系为谷子玉米柠条大豆大黄花苜蓿,谷子、玉米、柠条、大豆、大黄花各自硝态氮和水溶性磷的流失总量基本相同(P0.05);土壤剖面硝态氮含量随着深度增大呈现出峰值特征,且峰值存在的深度不同,土壤有效磷主要积聚在表层5 cm以上,5 cm以下含量极低。综上可知,野外草本植被在拦截径流、减少土壤侵蚀和控制养分流失方面要优于农田作物,在植被恢复中应广泛采用农地撂荒的方式进行恢复。

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

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.