Rill And Interrill Erosion Process In Ridging Systems In Brown Soil

Soil erosion is the most important global eco-environmental problems.Brown soil,as an important forest soil and agricultural soil,has been suffered from serious soil erosion because of the long-term cultivations which threated the food and ecological security.Slope is the basic unit of soil erosion including rill and interrill erosion.Rainfall type and slope are the main parameters influencing soil erosion.Ridging systems could influence soil erosion process through changing runoff and converge process.Therefore,Quantifing the effect of rainfall type and slope on the interrill,rill erosion process and their lumped process,i.e.,slope erosion process,could help to understand the process of soil erosion in soil sloping land and to the prevention and control of soil erosion in brown soil area using ridging systems.In order to deeply understand the soil erosion mechanism of ridged farmland on brown soil,this paper designed two rainfall types,namely,increased-type(70-70-100-100 mm/h)and detreased-type(100-100-70-70 mm/h),and artificial simulated rainfall were tested on 2 slopes(9° and 18°).Each rainfall type was divided into two phases(phase I,phase II),and two sessions of rainfall of the same rainfall intensity at each stage,and each session of rainfall lasts 20 minutes.A 1.60 m × 0.53 m plot was used and the rare earth elements lanthanum(La)and cerium(Ce)mixed in the soil of the ridge slope and the forrows to distinguish rill and interrill erosion.This paper investigated the erosion process of brown soil ridge and furrow system under different rainfall types and slopes,and the effects of rainfall types and slopes on rill geometry,rill erosion and intrerill erosion process.The results showed that:(1)Rainfall intensity had a significant effect on runoff and slope had different effects on runoff and sediment yield under different rainfall patterns.The time sequence of the same rainfall intensity in the process of rainfall had influence on runoff and sediment yield.Under 100 mm/h rainfall intensity,the time sequence of rainfall intensity presented no significant effect on sediment yield,and under 70 mm/h rainfall intensity,sediment yield was relatively small.The relationship of cumulative sediment yield and runoff was preseted as a power function.The order of total runoff from large to small was 9° decreased-type > 18°decreased-type > 9° increased-type > 18° increased-type,and the order of total sediment yield from large to small is 18° ncreased-type > 18° deteased-type > 9° dereased-type > 9° increased-type.(2)The interrill erosion on different slopes showed a trend of increase and then decreased pattern as the duration of rainfall prolonged.Under the increased rainfall pattern,the slope had a significant effect on the interrill erosion,but in the different stages of rainfall in the decreased rainfall intensity pattern the effect of slope on interrill erosion was different.In the detreased rainfall intensity pattern,the contribution rate of interrill erosion was decreasing in the stage I rainfall,but it was stable in the stage II rainfall.The time sequence of the same rain intensity in different rain patterns lead to the different interrill ersoion.The amount and contribution rate of total interrill erosion were different under different slopes.The order of total interrill erosion was 18° intreased--type > 9° intreased--type > 9° decreased-type > 18°decreased-type,and the order of total rill erosion contribution rate was 9° intreased--type > 9°decreased-type > 18° intreased--type > 18°decreased-type.(3)In different slopes and rainfall stages,there are differences in the rill form and erosion process.The cumulative length of rills on 18° slope was 1.14 times and 1.00 times of that on 9° slope,the average width of rills was 0.44 times and 0.20 times,and the average depth of rills was 2.85 times and 4.24 times,respectively.In stage I rainfall,under 70 mm/h rainfall intensity,the rill erosion amount and contribution rate of 9° and 18° slope surface are both 0,but under 100 mm/h rainfall intensity,the rill development was obvious,and the slope has significant influence on rill erosion amount.In stage II rainfall,under different rainfall intensity,the slope had significant influence on rill erosion amount.The total rill erosion amounst and the contribution rate of total rill erosion were consistent,and the order was 18° dereased-type > 18° increased-type > 9° detcreased-type > 9°increased-type.According to the linear fitting of stage I and stage II rainfall,under different rainfall patterns,the cumulative rill erosion on 9° and 18° slopes decreases by 93.34% and 94.80%,respectively,after the rainfall intensity changed under the detreased-type rainfall intensity.