Effect Of The Changing Of Antecedent Soil Moisture And Vegetation Cover On Interrill Erosion On The Slope Surfcae

In recent years, with the vegetation cover growing on the Loess Plateau, interrill erosion occurred more frequently on the slope surface. Antecedent soil moisture and vegetation cover were the major factors which affected soil erosion. Under field conditions, these parameters were likely related and there existed a close correlation relationship between antecedent soil moisture and vegetation cover. The objective of this study was to explore the effect of the combined effects of vegetation cover and antecedent soil moisture on interrill erosion on the slope surface. Two batches of artificial simulated experiments were conducted in different time. The first batch of experiment was conducted on interrill erosion of slope surface using simulated rainstorms(intensity 77±4.5 mm h-1; 60 minutes duration) on a light loamy soil under different levels of wheat-seedling cover and antecedent soil moisture produced by different sprayed applications of water(30, 40, 50, 60 or 70 mm). The objective was to explore whether existed an interaction between the two factors and the erosion condition under the interaction. The second batch of experiment was conducted on interrill erosion of slope surface using simulated rainstorms(intensity 90 mm h-1; 60 minutes duration) on a light loamy soil under different levels of ryegrass cover and antecedent soil moisture produced by different sprayed applications of water(60, 90, 120 or 150 mm). It was a complete random combination experiment(4×4) and the objective was to explore the erosion condition under each factor and their interaction respectively. Based on the second batch of experiment, other following experiments like effect of aging duration and effect of overground part and root of ryegrass on interrill erosion were conducted under the same simulated rainstorms. Some main results were obtained as follows:(1) There existed an interaction between vegetation cover and antecedent soil moisture. Effect of the two factors on interrill erosion of slope surface was complex. With the water levels changing, the roles that vegetation cover and antecedent soil moisture played respectively were different. Under the relatively low vegetation cover, as in the first batch of experiment that the range of wheat-seedling covers was from 9.7% to 37.2%, the effect of vegetation cover was obscured by antecedent soil moisture. Then, under the relatively high vegetation cover, as in the second batch of experiment that the range of ryegrass covers was from 44.1% to 65.8%, vegetation cover played a main role in controlling the soil erosion process. It can be seen that the roles that vegetation cover and antecedent soil moisture played respectively in controlling the soil erosion were changing and relative.(2) Aging duration was the collection of a series of factors that affecting interrill erosion on the slope surface. It affected soil erosion by affecting antecedent soil moisture, vegetation cover, soil crust and so on. Under each treatment, the effects of aging duration on runoff were not same. Initial antecedent soil moisture had much effect on runoff rate by affecting the aggregate stability. In the low soil moisture zone, runoff rate was relatively high when the aging duration was 0 day. But in the high soil moisture zone, the result was opposite. With the aging duration increasing, the erosion rate on slope surface was reduced significantly. Under the relatively high initial ryegrass cover(44.1~65.8%), the increasement of vegetation cover played a main role in controlling interrill erosion, and the effect of antecedent soil moisture was obscured.(3) Ryegrass cover can affect the time to runoff and added 0.97 min contrast to the control treatment on average. In that, the overground part of ryegrass was a predominate factor that affecting the increasement of time to runoff which can added 0.90 min. However, the root of ryegrass nearly had no effect on time to runoff.Ryegrass cover was not related to runoff rate closely. But the overground part of ryegrass had much effect on the reduction of runoff rate. The runoff rate reduced 10 mm h-1 on average. Ryegrass cover played a main role in reducing the soil loss and the average sediment reduction benefit was 83.2%. The sediment reduction benefit increased with the vegetation cover growing(R2=0.4092,P<0.01,N=48). The soil loss reduced by overground part and root of ryegrass accounted for 21.0% and 79.0% of the total sediment reduction amount on average respectively. These suggested that the root of ryegrass played a main role in reducing sediment yield, but the overground part of ryegrass mainly had effect on reducing the runoff. In addition, the effect of vegetation cover on interrill erosion rate of slope surface was much more than runoff rate and antecedent soil moisture.