Effects of Embedded Gravel or Gravel Mulching in Southern Red Soil on Slope Sediment Yield and Runoff

The red soil hilly region of southern China is affected by rainy seasons (Meiyu periods). There can be large variations of total rainfall per event and rainfall vs. time. This region is therefore sensitive to rainstorms during the Meiyu periods. Rainfall can cause soil coarsening in some areas and the resulting soil contains large amounts of gravel. This form of soil erosion is serious in southern China where there is heavy rainfall and the soil layer is thin. Gravel mulching has been shown to affect soil moisture content, hydraulic conductivity, infiltration, and evaporation. We used simulated rainfall experiments to study the effects of soil surfaces with embedded gravel or gravel mulching on slope runoff and sediment yield for Southern red soils under different rainfall intensities and slope gradients. Both gravel treatments reduced sediment and runoff vs. soil with no gravel, but the amount of reduction varied. Runoff did not consistently increase with slope gradient and rainfall rate. At low rainfall intensity, embedded gravel and gravel mulching inhibited runoff formation, but at high rainfall intensity and steeper slopes, the level of inhibition was reduced. The findings are important for soil conservation and management relative to gravel content, particularly in areas of China with substantial contents.