Study On Effects And Mechanisms Of Runoff And Erosion Process From Sloped Farmland With Straw Incorporation

Returning straw into farmland is one of the important utilization measures of farmland residues.Straw incorporation into cultivated layer can improve soil structure,increase soil organic matter,and affect the hydrological microcirculation process and soil erosion process.In this study,the cultivated soil incorporated with straw was taken as the research object,and it was compared with the soil without straw incorporation.Laboratory simulated rainfall experiments with a silt loam soil were conducted to examine the effects of straw incorporation into cultivated soil layer on slope hydrological erosion,under different straw incorporation rates(0,2,4,8 t/ha),slope gradients(10,15,20°)and rainfall intensities(80,120,160 mm/h).During the whole rainfall process,the sediment-laden flow samples were collected at a pre-determined time period and time interval to quantitatively analyze the variation law of soil and water loss process.The total rainfall amount was 100 mm in all experimental runs,which were performed in triplicate.By observing the experimental processes and analyzing experimental date,the main results are as follows:(1)Straw incorporation can delay the runoff initiation time periods on slope.The runoff initiation time periods of straw incorporation slope were 1.02-2.41 times of that of control group(0 t/ha);the runoff initiation time periods of 4 t/ha and 8 t/ha straw incorporation slope were about 1.03-1.27 times that of 2 t/ha.As the straw incorporation rate was increased,the slope resistance and soil water channel increased,and led to a delayed effect on the runoff initiation time periods.However,a greater rainfall intensity results in a rise in rainfall recharge and a steeper slope gradient has greater the slope driving force,thus the runoff generation occurred earlier.(2)Straw incorporation can reduce rainfall runoff,and the runoff rate increased with the cumulative rainfall.After runoff initiation,the runoff rate of the control group(0 t/ha)increased faster than the other groups under straw incorporation at different rainfall intensities and slope gradients.And the growth trend of runoff rate decreased with the decrease in the straw incorporation rate.With the rainfall intensities and slope gradients increasing,the runoff rate increasing.It is worth noting that the runoff fluctuates with the rainfall duration,and the greater the rainfall intensity,the greater the runoff fluctuation.As the rainfall duration increases,the influence of the slope gradient on the runoff is overshadowed by those of the straw incorporation rate and rainfall intensity,which led to the average runoff intensity affected by rainfall intensity more than slope gradient.(3)Straw incorporation into soil affects soil infiltration process,and can be modelled well using the Kostiakov model(R~2>0.95).As the advance of rainfall duration or the cumulative rainfall increasing,resulted in a fluctuating decrease in the infiltration rate and an exponential increase in the cumulative infiltration.The reason for this phenomenon is that straw incorporation into soil increases soil porosity,and straw exposed to the surface reduces rainfall kinetic energy,thereby increasing soil infiltration.But with the cumulative rainfall increasing,the random fluctuations in the infiltration rate corresponded to the formation and destruction of soil crust.In addition,a greater slope reduced the rainfall interception area and caused soil infiltration decrease;a greater rainfall intensity increased the driving force of water infiltration and accelerated the increase of soil infiltration,but weakened the effect of straw incorporation on controlling hydrological process.(4)Straw incorporation into the tillage layer increased the anti-erodibility by improving the stability of the soil structure,it can significantly decrease sloping rainfall erosion.The 2,4,and 8 t/ha straw incorporation slope reduced the sediment concentration by22.7,55.5 and76.9%,and the sediment delivery rate by 34.6,66.5 and 85.6%,as well as the cumulative soil loss by 34.5,70.0 and 84.9%,respectively,compared with those of 0 t/ha straw incorporation rate.The results showed that straw incorporation into soil had a positive impact on sediment concentration,sediment delivery rate and soil loss,and the sediment reduction effect was more than 75%at a straw incorporation rate of 8 t/ha.With the increase of straw incorporation rate,the discrete degree of sediment concentration and sediment delivery rate decreased during rainfall runoff process.With the rainfall intensity and slope gradient increasing,the eroded sediment yields increased.In sum up,straw incorporation increases surface roughness and water infiltration area,affects soil infiltration and rainfall runoff,changes soil hydraulic characteristics,and makes soil erosion change significantly,rainfall intensity and slope gradient were also important factors.This study can provide data basis for farmland soil and water conservation research and practice.