Effects Of The Half-ridge Planting Measure For Contour Ridges On Soil Erosion Characteristics At The Black Soil Hillslopes

The Northeast black soil region is essential to Chinese food security and sustainable development.However,soil erosion is severe due to long-term over-cultivation and utilization,climate change,and other factors.The black soil has become thinner and harder,which is threatening sustainable agricultural development.In order to prevent and control the soil erosion hazard,conservation tillage measures have been explored for many years in the Chinese black soil region.Among them,some areas in Jilin Province have promoted a maize half-ridge planting measure for contour ridges according to the local climate and terrain characteristics,which only uses one side of the ridge for cultivation.The other side of the ridge is in the leisure state in the cultivation year.It implements alternate-year rotation planting and reverse crop fallow,finally realizing the resting and nourishing of the land simultaneously and maximizing the protection of local soil resources.However,since this half-ridge planting measure is relatively new,which needs to be clarified how effective it is in preventing soil erosion.Therefore,this thesis simulated the half-ridge planting measure for contour ridges based on cross-slope ridge cultivation by controlling soil bulk densities.The treatments with different bulk densities for contour ridges included all looseness(the soil bulk density was 1.00 g/cm~3),upper looseness+lower compaction(the soil bulk densities were 1.00 and 1.20 g/cm~3,respectively),upper compaction+lower looseness(the soil bulk densities were 1.20 and 1.00 g/cm~3,respectively)and all compaction(the soil bulk density was 1.20 g/cm~3,respectively).Thus,based on simulated rainfall and confluence experimental methods,the effects of half-ridge planting measure for contour ridges on soil erosion characteristics,shapes of contour ridges,and hydrodynamic characteristics were analyzed.The main research findings are as follows:(1)Under the rainfall experimental conditions,compared with the all looseness treatment,the runoff volumes of the upper compaction+lower looseness and all compaction treatment were reduced by 16.1%-19.4%and 6.6%-11.4%,respectively;and the soil erosion volumes were reduced by 25.0%-52.5%and 17.9%-31.6%,respectively.The overall soil erosion volume showed that all looseness>upper compaction+lower looseness>all compaction>upper compaction+lower looseness.At the same time,the half-ridge planting measure for contour ridges also had a better effect of regulating the runoff erosion processes,and the changes of its runoff rates and soil erosion rates with rainfall duration are relatively stable.Therefore,the half-ridge planting measure for contour ridges could regulate runoff and soil erosion under the rainfall experimental conditions.(2)Under the confluence experimental conditions,the runoff volume was minimum for the all looseness treatment at 1.25 L/min confluence intensity.Compared with the all looseness treatment,the runoff volumes of the upper compaction+lower looseness treatment reduced by 8.0%-10.2%at 1.67 L/min confluence intensity;furthermore,the soil erosion volume of the upper compaction+lower looseness and all compaction treatments decreased by 33.3%-54.1%and 42.4%-60.8%,respectively.The runoff rates and soil erosion rates of the half-ridge planting measure for contour ridges varied relatively smoothly with the confluence duration.Thus,the half-ridge planting measure for contour ridges could regulate runoff and soil erosion under the confluence experimental conditions,especially for conditions with greater confluence intensity,which might show more obvious runoff and soil erosion reduction effects.(3)Compared with the all looseness treatment,the top width,top spacing,and depth of ridge furrow for the upper compaction+lower looseness treatments increased by 0.4-1.3 cm,0.3-3.3 cm,and 1.1-1.5 cm,respectively,and the width of ridge furrow reduced by 0.1-3.3cm under the rainfall experimental conditions;the top width,top spacing,and depth of ridge furrow for the upper compaction+lower looseness treatments increased by 0.5-0.8 cm,1.0-1.5 cm,and 0.5-0.8 cm,respectively,and the width of ridge furrow reduced by 0.9-1.2cm under the confluence experimental conditions.By comparing the variation of ridge shape under rainfall and confluence experimental conditions,it was found that the variation value and amplitude of ridge shape under experimental conditions were higher than that under confluence experimental conditions.Moreover,the all compaction treatment had little change in ridge shape and had obvious effect on maintaining ridge stability and reducing soil erosion.Therefore,the half-ridge planting measure for contour ridges could effectively prevent the decrease in the width of ridge furrow,and thus promote the stability of contour ridge shape.(4)The hydrodynamic parameters of the black soil hillslope showed corresponding changes due to the application of half-ridge planting measure for contour ridges.Under the lower rainfall/confluence intensity conditions,the all looseness treatment showed the smallest Reynolds and Froude numbers,and he largest resistance coefficient and runoff shear.Compared with the all looseness treatment,the Reynolds number of the upper compaction+lower looseness treatment decreased by 15.1%-19.0%,and the runoff shear increased by16.3%-19.1%at the 100 mm/h rainfall intensity;the Reynolds number of the upper compaction+lower looseness decreased by 2.7%-10.2%and the runoff shear increased by8.3%-9.9%at the 1.67 L/min confluence intensity.Thus,the half-ridge planting measure for contour ridges had obvious effects on reducing the average flow velocity of hillslope runoff,Reynolds and Froude numbers,and increasing the slope resistance coefficient and runoff shear force under greater rainfall/confluence intensities.In conclusion,the half-ridge planting measure for contour ridges could regulate runoff and soil erosion under both rainfall and confluence experimental conditions by comparing with the all looseness treatment.Furthermore,the half-ridge planting measure for contour ridges could effectively promote the stability of contour ridge shape and change the hydrodynamic parameters of the black soil hillslope.Thus,the half-ridge planting measure should be systematically studied and scientifically selected according to the specific rainfall/confluence characteristics and topographic slope gradients of farmlands to improve its implementation in the black soil region.