Effects of Different Rates of Straw Mulch on the Runoff and Sediment Yield of Young Citrus Orchards in Lime Soil and Red Soil in Studies with a Rainfall Simulator

Soil erosion has been a major environmental issue in young citrus orchards in karst areas of Southwest China. Straw mulching is an effective measure to reduce soil erosion. However, few studies have considered this measure in soil and water conservation in citrus orchards in karst areas. In this study, the effects of straw mulching on runoff and sediment reduction in young citrus orchards were studied using the simulated rainfall method with two typical soils—red soil and lime soil—in karst areas. This study consisted of two rainfall intensities (60 and 120 mm/h) and four straw coverages (0, 20, 50, and 80%). The results showed that straw mulching can significantly reduce surface soil loss in both lime soil and red soil. The surface runoff reduction rate of lime soil with straw mulching was much higher than that of red soil. Under the condition of heavy rainfall (120 mm/h), the surface soil loss rate was reduced by more than 57.5% in lime soil with 20% straw mulching. In red soil, a similar reduction rate of soil loss can only be achieved when straw mulching is 50%. Straw mulching reduced the surface soil loss of lime soil in young citrus orchards, mainly because of limited runoff transport, while red soil was limited by soil stripping. The results can provide a scientific basis for soil and water conservation in young citrus orchards in karst areas.