Effect Of Biochar Addition On Soil Erosion On Loess Slope And Its Mechanism

The intense soil erosion on the Loess Plateau has led to serious soil degradation on the slopes,and it is urgent to repair and improve them to ensure food security and sustainable high-quality development of dryland agriculture,and to consolidate the results of returning farmland to forests and grasses.Biochar has attracted much attention as a soil amendment because of its special properties and multiple functions after being imported into the soil.However,existing research mainly focuses on the effects of biochar addition on soil physical and chemical properties,nutrients,crop yields,etc.There is a lack of a unified understanding and systematic theoretical explanation for the changes in soil erosion characteristics driven by the addition of biochar,which makes it impossible to determine whether it is available to be applied to repair and improve degraded soil.In view of this,this study takes loessial soil in the Loess Plateau as the object,and based on the long-term location monitoring experiment of field plots,it analyzes the effects of biochar addition on soil physical and chemical properties,water parameters,rill erodibility,inter rill erodibility,and slope soil erodibility.Based on the influence of erodibility and runoff and sand production on slopes,the system reveals the mechanism of the impact of biochar addition on the slope erosion process,providing for the rational use of biochar to improve degraded slopes and formulating slope soil erosion control strategies under the conditions of biochar addition scientific basis.The main research conclusions are as follows:1.The variation of the physical and chemical properties of loessial soil has been cleared under the biochar application.The addition of biochar increases the content <0.002 mm effective particle size,specific surface area of soil particle,total carbon and organic carbon,and reduces the content of 0.05-2 mm effective particle size,effective median particle size and soil bulk density.The effect of biochar on non-capillary porosity and pH is not significant.The soil total porosity,capillary porosity,>0.25 mm soil waterstable aggregate and the average weight diameter of aggregates increased by 7%,8%,42% and 40%,respectively.The content of <0.002 mm and 0.002-0.05 mm effective particle size,specific surface area,total porosity,capillary porosity,aggregate stability,total carbon and organic carbon increase with the increase of biochar addition amount.The content of 0.05-2 mm effective particle size,effective median particle size,noncapillary pores,and soil bulk density showed a decreasing trend with the increase of biochar addition amount.The addition of biochar has a significant time effect on the physical and chemical properties of the soil.With the increase of years after the addition,the content of 0.05-2 effective particle size,median particle size,bulk density and shear strength show an increasing trend.The total pores,capillary and non-capillary porosity,aggregate stability,total carbon,organic carbon and pH showed a decreasing trend.2.The variation of the water characteristic parameters of loessial soil has been cleared under the biochar application.After two years,Biochar addition reduced the infiltration rate,the soil infiltration rate gradually increased and was positively correlated with the amount of addition.The addition of biochar significantly improved the soil water holding capacity and was proportional to the amount of biochar added.The field water capacity under each biochar treatment increased by 6%,11%,13%,10% and 30%,respectively.The addition of biochar increases the soil water content of 0-100 cm,especially the soil water content of the cultivated layer,and the effect is proportional to the amount of biochar.The increase is significanr from May to September,especially in the rainy season.3.The effect of biochar addition on the detachment capacity by rill flow and rill erodibility of loess slope has been clarified.The addition of biochar reduced the detachment capacity by rill flow and the increase of the detachment capacity by rill flow with the increase of slope and flow.This reduction effect weakened with the increase of biochar addition and the extension of time after addition.The flow power is the optimal hydrodynamic parameter describing the kinetic process of detachment capacity by rill flow under the addition of biochar.The addition of biochar reduces the rill erodibility,and the degree of reduction is proportional to the amount of biochar added and the number of years experienced after addition.4.The effect of biochar addition on the sediments and runoff has been clarified.Both micro-runoff(length×width 1 m×0.6 m)and conventional runoff plots(length×width 9m×2 m)added biochar to reduce runoff and soil loss and weaken the sensitivity of runoff and soil loss for slope and the maximum 30 min rain intensity,and weakening effect is proportional to the amount of biochar added.The effect of biochar addition on rainfall with long duration and low rainfall erosivity is better than that of short duration,high erosive rainfall.The addition of biochar reduces the erodibility between the rill erodibility and the erodibility of the slope soil,and the degree of reduction is proportional to the amount of biochar added.5.The mechanism of the influence of biochar addition on soil erosion on loess slopes is revealed.The addition of biochar directly affects the physical and chemical properties of soil,and indirectly affects the erodibility of rill erodibility,the inter-rill erodibility,the erodibility of slope soil and the runoff force,and ultimately affects the process of soil erosion on the slope.The addition of biochar affects rill erodibility by changing key factors such as the specific surface area of soil particles,organic carbon,water content,non-capillary porosity,and the average weight diameter of aggregates.By changing the effective particle size content of <0.002 mm,organic carbon,Key factors such as shear strength,non-capillary porosity,average weight diameter of aggregates,and stable infiltration rate affect the inter-erodibility and the erodibility of slope soil.Structural equation model(SEM)results show that the impact of key factors on rill erodibility is soil aggregate content(-0.58)> soil particle specific surface area(-0.42)>soil water content(0.41)>soil organic matter content(-0.31)>soil non-capillary porosity(-0.28);the order of the magnitude of influence on the erodibility and runoff force between rills is <0.002 mm(-0.71)> shear strength(-0.52)> aggregate content(-0.48)>organic carbon content(-0.41)> stable infiltration rate(-0.29)> non-capillary porosity(-0.28),the order of influence on slope soil erodibility and runoff force is organic carbon content(-0.58)> stable infiltration rate(-0.57)> shear strength(-0.47)> <0.002 mm content(-0.37)= non-capillary porosity(-0.37)> aggregate content(-0.29).It shows that there are differences in the key factors of the slope erosion characteristics caused by the addition of biochar under different plot sizes and erosion methods.