Effects Of Rainfall Intensity And Inflow Rate On Hillslope Water Erosion Process Under Longitudinal Ridge Tillagen In The Thinner Black Soil Region Of China

Soil erosion in the black soil region of Northeast China is severe due to long-term unreasonable farming system and unique long-slope landforms.This study used observation of field runoff plots and simulated rainfall and runoff methods to study the effects of rainfall intensity and inflow rate on hillslope water erosion process under longitudinal ridge tillage in black soil region of northeast China and provided the scientific information for controlling hillslope soil erosion.The simulated expreiments covered two types of tillage methods(longitudinal ridge and non ridge with bare and fallow),two rainfall intensity(50 and 100 mm h-1),and 5 upslope inflow rates(10,20,30,40,50 L min-1)and 5° slope gradient.The treatment of field runoff plots included two tillage methods with longitudinal ridge and non ridge and one 5° slope gradient.The main conclusions were as follows:(1)Effects of rainfall intensity on hillslope erosion were studied.Data observed from field runoff plots during 2012-2015 showed that erosive rainfall had important influences on hillslope erosion under longitudinal ridge and non redge treatments.Soil loss increased by 2.4 times when the annual erosive rainfall increased by 2.2 times.Morepver,compared with non-ridge under 5°slope gradient,runoff rate at longitudinal ridge treatment decreased by 66.4% and soil loss decreased by 72.2%.Under the rainfall simulated expreiments,when rainfall intensity increased from 50 mm h-1 to 100 mm h-1,hillslope runoff rate increased at longitudinal ridge treatment by 1.5 times and Hillslope soil loss increased by 9.2 times.(2)Effects of upslope inflow rates on hillslope water erosion were analyzed.When inflow rates increased by 10 L min-1,hillslope runoff rate and soil loss at longitudinal ridge treatment increased by 35.8%-571.5% and 33.6%-800.1%,respectively.When inflow rate increased from 20 to 40 L min-1,hillslope runoff rate and soil loss at longitudinal ridge treatment increased by 49.5%-63.6% and 52.1%-67.5%,respectively.As upslope inflow rate changed from 10 to 20 L min-1,there was no significant difference between both treatments of the non-ridge and longitudinal ridge treatment.When upslope inflow rate shifted from 30 to 50 L min-1,hillslope runoff rate and soil loss under the longitudinal ridge treatment was less than that under the non-ridge treatment.(3)Effects of rainfall intensity and inflow rate on hillslope water erosion were discussed.Effects of upslope inflow rate on hillslope runoff were greater than that of rainfall intensities on runoff;while effects of upslope inflow rates on soil loss were smaller than that of rainfall intensity on soil loss.Compared with the non redge treatment,runoff rate and soil loss at longitudinal ridge treatment decreased by 9.0%-23.7% and 13.5%-28.4%,respectively.(4)Effects of upslope inflow rate on hydraulic and hudrodynamic parameters were analyzed.When inflow rate was 10-20 L min-1,the flow velocity at the longitudinal ridge treatment was greater than that at the non-ridge treatment.As inflow rates changed from 30 to 50 L min-1,runoff velocity at the longitudinal ridge treatment was smaller than that at the non-ridge treatment.With the increase of inflow rate,the Darcy resistance coefficient decreased by 2.2%-41.7%;while the average runoff velocity and shear stress increased by 9.4%-31.5%,and by 2.9%-123.2%,respectively.