| In recent years,the situation of soil and water loss in Northeast China has become more and more serious,which leads to the degradation of ecosystem function,sediment transport and river deposition,thus restricting the sustainable development of local agricultural production and causing serious environmental problems.Therefore,it is of great significance to find out the factors that affect the soil and water loss in the black soil area of Northeast China and reduce the degree of soil and water loss in the sloping farmland,so as to improve the utilization efficiency of regional soil and water resources and maintain a good ecological environment.Based on the Songnen Plain in the northeast of China,by adding biochar to the sloping land in the black soil area,this paper explores the influence of biochar on the water and sediment transport process and the hydrodynamic mechanism of rill erosion under the condition of seasonal freezing and thawing.The experiment set up four slopes of 1.8,3.6,5.4 and 7.2°to add two biochar content treatments:biochar content 6 kg·m-2（B6 treatment）and 12 kg·m-2（B12 treatment）and blank control group:biochar content 0 kg·m-2（B0 treatment）,In the same period（spring thawing period）in 2018 and 2019,the artificial rainfall simulation test was carried out to measure and calculate the flow velocity and water depth,Reynolds number,Froude number,flow resistance coefficient and other parameters in the rill,and analyze the impact of biochar on the water and sediment transport process on the slope and the change of the hydrodynamic parameters of rill erosion.The main conclusions are as follows:（1）The experimental results show that after one year and two years of seasonal freezing and thawing,the application of biochar can effectively reduce the runoff on the slope and slow down the runoff rate.Among them,after one year’s seasonal freezing and thawing,the decrease range of runoff velocity rate of B6 and B12 treatments was 19.1%～27.9%and 24.4%～29.5%respectively.After the second year,the decrease range was weaker than that of the first year;Compared with the first year,in the second year,the range of sediment concentration of B6 and B12 treatments decreased by 5.5%～14.8%and 3.3%～13.6%,respectively;Biochar had a great influence on rill erosion,in the second year after freezing and thawing,B6 and B12 treatments reduced gully erosion by 25.1%～35.1%and 31.7%～51.4%respectively.（2）The flow pattern of rill flow on the slope mostly belongs to turbulence and critical flow.The Reynolds number Re of rill flow on the slope treated by B6 and B12 decreases with the increase of time duration,and its critical erosion power values are0.403 Pa、0.098 m·s-1、0.002N·m-1,0.497 Pa、0.124 m·s-1、0.003 N·m-1,respectively,in 2018 and 2019,it can be seen that the increase of duration and seasonal freeze-thaw times can promote the development of biochar controlled water and sediment transport process and rill.（3）After two years of freezing and thawing,biochar was applied to different slopes,and the soil loss rate was significantly correlated with biochar content and slope.Through stepwise regression analysis,the model 1 was established:"Dr=-1.709+4109.894φ（R2=0.861）"as the equation based on unit water power and soil loss rate;model 2:"Dr=-12.763+2184.619φ+8.366S（R2=0.907）"is the equation based on unit flow power and slope and soil loss rate;model 3is the linear equation based on unit flow power,slope and biochar content and soil loss rate"Dr=-6.039+1072.131φ+12.246S-1.470B（R2=0.938）".Through accuracy test and analysis,model 3is the optimal soil loss prediction equation.To sum up,through the experiment and data analysis of the slope farmland in the northeast black soil area,it is concluded that the application of biochar has a positive effect on reducing the soil erosion on the slope.The expected research results have important theoretical and practical value for alleviating the soil erosion and farmland degradation in the Northeast Black soil area and formulating scientific and reasonable soil erosion control strategies. |
