Effects Of Litter Covering And Incorporating Into The Soil On The Runoff And Sediment Generation Of The Loess Slope

In recent years,the vegetation on the Loess Plateau has been significantly restored,resulting a large accumulation of surface litter,while the related research on the effects of litter on the soil erosion process lags behind.At present,the related researches on the effects of litter on the process of soil erosion are mostly concentrated on the effects of litter coverage on the slope runoff and sediment yield process.There is few quantitative research about the effect of litter biomass on runoff and sediment generation or overland flow hydraulic condition.In addition,the incorporation of litter into the soil can also significantly affect the soil erosion process on the slope,while the impact of litter on the process of runoff and sediment generation on the slope is rare,especially the quantitative relationship between them.Besides,the effects of incorporated litter on the runoff and sediment yield on the slope is rarely reported.Therefore,we selected the litter of Artemisia sacrorum Ledeb?compositae plant?and Bothriochloa ischcemum?Linn.?Keng.?gramineous plant?as the research objects in the hilly-gully region of the Loess Plateau.According to the distribution characteristics of litter in the field,seven litter mass levels were set.The litter mass coverage of Artemisia sacrorum Ledeb.was 0,100,200,400,600,800,and1000 g m^-2.While the litter of Bothriochloa ischcemum?Linn.?Keng was 0,50,100,150,200,350,600 g m^-2.For two kinds of litter,the mass of litter incorporated into topsoil?0⁵cm?were consistent with its mass coverage.To systematically study the effects of typical grassland litter covering and incorporating into soil on slope runoff and sediment yield,we conducted artificial simulated rainfall experiments and came to main conclusions as follow:?1?The litter covering the soil and incorporating into the soil can significantly affect the overland flow hydrodynamic characteristics.With the increase of litter covering mass,the Reynolds number,Froude number and average flow velocity decreased as a power function?p<0.01?,while the resistance coefficient increased as a power function?p<0.01?.When the litter incorporation mass increased,the Froude number and the average flow velocity decreased as a power function,while the resistance coefficient increases as a power function?p<0.01?.For the two litters,the overland flow velocity in the litter covered treatment was lower than that of the litter incorporation treatment,which was reduced by68.79%and 60.29%,respectively.The resistance coefficient was larger than the incorporation,which was 144 and 15 times,respectively.Under the same conditions of litter biomass,the average flow velocity in litter covered treatment and the treatment incorporated with Artemisia sacrorum Ledeb.litter were lower than that in the treatment incorporated Bothriochloa ischcemum?Linn.?Keng litter,which decreased by 24.42%and13.63%,respectively.However,the resistance coefficient was higher than that of Bothriochloa ischcemum?Linn.?Keng,which were 9.27 and 1.78 times of that of Bothriochloa ischcemum?Linn.?Keng.?2?Both litter covering and incorporating into soil can effectively delay the initial runoff time.Compared with the bare soil control,the initial runoff time of Artemisia sacrorum Ledeb.litter covering and incorporating were 8.49 and 2.51 times of the bare soil,respectively,and that of the Bothriochloa ischcemum?Linn.?Keng litter were 4.97 and 1.77times,respectively.With the amount of litter covering and incorporating increase.the effects of delaying initial flow time enhanced as a whole.The initial runoff time of the treatments of litter covered by Artemisia sacrorum Ledeb.and Bothriochloa ischcemum?Linn.?Keng.were higher than that of the treatment of litter incorporated into soil,which was 3.38 and 2.81 times greater,respectively.Under the condition of litter covering and incorporating,the rate of runoff showed a trend of increasing first and then stabilizing with the process of rainfall.With the mass of litter coverage increasing,the runoff yield decreased as a power function?p<0.01?,and with the mass incorporated increasing,the runoff yield did not change significantly.For the treatments covered by Artemisia sacrorum Ledeb.and Bothriochloa ischcemum?Linn.?Keng.litter,their runoff yield were lower than that of the treatments incorporated litter,which decreased by 4.21%and 7.21%,respectively.?3?Under the conditions of litter coverage and incorporation,the rate of sediment increased with the process of rainfall,but it was affected by the rainfall intensity and the amount of litter covering or incorporating.The litter covering or incorporating into soil can significantly reduce the sediment yield.Compared with the bare soil control,For the treatment covered and incorporated of Artemisia sacrorum Ledeb.litter,their sediment yield decreased by 91.44 and 44.22%,respectively.While the treatment of Bothriochloa ischcemum?Linn.?Keng.litter decreased by 52.36%and 34.34%,respectively.With the litter mass increased,the sediment yield of two kinds of litter were decreased as a power function?p<0.01?.When the amount of litter coverage was the same,the sediment yield of Artemisia sacrorum Ledeb.litter decreased by 56.55%compared with that of Bothriochloa ischcemum?Linn.?Keng..When the amount of litter incorporation was the same,the sediment yield of Bothriochloa ischcemum?Linn.?Keng.decreased by 15.62%compared with that of Artemisia sacrorum Ledeb..?4?Overland flow hydrodynamic parameters and litter characteristics are closely related to sediment yield.Under the condition of litter cover,the sediment yield increased with the increase of Reynolds number,Froude number,average flow rate and runoff yield,and decreased with the increase of resistance coefficient?p<0.01?.The sediment yield can be characterized as the power function relationship between the runoff yield and the mass of litter?p<0.01?.Under the conditions of litter incorporation,the sediment yield increased with the increase of the Froude number and the average flow velocity,while decreased with the increase of the resistance coefficient?p<0.01?,and the total sediment yield can be characterized as the power function relationship between the runoff yield and the litter volume.?5?The litter covering and incorporating into soil had better benefits of runoff and sediment reduction.Under the condition of litter cover,the benefits of flow reduction and sediment reduction increased with the increase of litter mass coverage.Under the condition of litter incorporation,although there was a certain flow reduction benefit,there was no significant relationship with the amount of litter incorporation,but the benefit of sediment reduction enhanced with the increase of litter amount.There were significant differences in the benefits of runoff and sediment reduction between two kinds of litter.When the amount of litter cover was the same,the benefits of runoff and sediment reduction of soil covered by Artemisia sacrorum Ledeb.litter were 1.22 and 1.36 times of that of soil covered by Bothriochloa ischcemum?Linn.?Keng.litter,respectively.When the amount of litter incorporation was the same,the benefit of runoff reduction of soil incorporated Artemisia sacrorum Ledeb.litter was 2.20 times of that of Bothriochloa ischcemum?Linn.?Keng.litter.The benefits of sediment reduction were opposite,only 65.28%of soil incorporated with Bothriochloa ischcemum?Linn.?Keng.litter.