Study On Change Characteristics Of Microtopography On Ridge Tillage And Its Effects On Soil Erosion

Ridge tillage is one of the most effective tillage measures to control soil and water losses on sloping farmland.However,the impact of ridge tillage on soil erosion remains controversial,it influenced the control of regional soil erosion and the reasonable layout of tillage measures.Therefore,this paper took the purple soil in Hilly Area of Central Sichuan Basin as the research object,methods involving artificial rainfall and laser scanning were adopted to investigate change characteristics of microtopography on ridge tillage and its effects on soil erosion under different rainfall patterns,slopes and erosion stages.Efforts are being made to find the critical conditions of runoff and sediment yield under the corresponding conditions.These findings had important implications for the prevention and control of soil erosion of purple soil area and laying a theoretical basis and a support datum for harnessing measure of sloping farmland.The main results were as bellowing:(1)The coefficient of variation of CV on all slopes were less than 1,indicated spatial variation of soil roughness on sloping farmland of purple soil is medium strength.In general,the standard deviation of SD under different rainfall conditions were RT>CK,indicated that the ridge tillage had a higher spatial variability.The soil erosion area of increased rainfall series was higher than that of decreased rainfall series for different tillage measures.When the slope is less than 15,the soil erosion area decreased gradually with the increase of slope.When the slope is greater than 15,the soil erosion area increased rapidly,and the soil erosion area of different tillage measures gradually expanded with the evolution of erosion stages.Under different rainfall conditions,the microslope of ridge tillage were mainly distributed in the southern and northern slopes,while the change of microaspect was more complex.(2)Under increased rainfall series,the soil roughness,f(a)max and △a of ridge tillageincreased with the increase of rainfall duration,microrelief tended to be sharp.Under decreased rainfall series,the soil roughness showed an increasing first and then decreasing trend,△fand △ a showed a trend of fluctuating downward and upward respectively with the increase of accumulated rainfall,microrelief tended to be round.The soil roughness and △ a of ridge tillage increased with the increase of slope,while △f(a)decreased with the increase of slope,and microrelief tended to be sharp with the increase of slope.Under different slope conditions,the soil roughness of ridge tillage showed a decreasing first and then increasing trend with the evolution of erosion stages,and the higher the slope,the greater the growth rate.△a increased gradually with the evolution of erosion stages,△f(a)were less than 0 at each erosion stages,microrelief tended to be sharp.Under different rainfall conditions,the base effect of the SM model of different tillage practices were all greater than 75%,which indicated that the spatiotemporal variability of the microtopography had strong autocorrelation and artificial tillage was the major contributing factor to the spatial heterogeneity of microtopography on sloping farmland.(3)Under different rainfall conditions,drainage networks of CK was divided into five orders,whereas the ridge tillage was divided into four orders.And drainage density and stream frequency of ridge tillage were lower than that of CK,which indicated that theconcentration degree of drainage networks increased with the increasing microrelief.The difference of the spatial distribution of drainage networks increased with the increase of slope.The drainage density of ridge tillage increased gradually with the increase of slope,which indicated that the higher slope,the more concentrated the drainage networks,while CK showed the opposite trend.Under different rainfall conditions,△D of ridge tillage were less than CK,indicated that spatial heterogeneity of drainage networks of ridge tillage is relatively low.(4)The effects of different rainfall patterns on the microtopography are different,and the increased rainfall pattern was more likely to cause soil erosion.R0 and R1/R0 had significant or extremely significant correlation with runoff and sediment yield,and f(a)max and △a had significant or extremely significant binomial correlation with runoff and sediment yield.The runoff rate,runoff yield,sediment rate and sediment yield increased with the increase of slope.Under different slope conditions,R0 and Ri/R0 had significant or extremely significant correlation with runoff and sediment yield,and f(a)axand △a had significant or extremely significant binomial correlation with runoff and sediment yield.The sediment rate and runoff rate of ridge tillage increased gradually with the evolution of erosion stages,and the differences increased with the increase of slope.The runoff and sediment yield on sloping farmland can be well predicted by using soil roughness,multifractal parameters of microtopography and drainage networks.