Effect of Soil Water Content on Runoff Production and Soil Loss from Rills in Field Experimental Plots in Different Slopes

Soil water content (SWC) is an important physical factor that plays an essential role in many processes such as infiltration and soil erosion. This study was conducted to investigate the effect of SWC on runoff and soil detachment from rills in coarse-grained soils in the semi-arid region. For this purpose, furrows with 6 m in length were installed in five rainfed farms with different slope steepness (6.1, 10.6, 14.8, 20.7 and 27.1%) treated with four moisture levels including air-dried (AD), between air-dried and field capacity (AD-FC), field capacity (FC) and saturation point (SP) in a completely randomized design witht three replications. Flow rate with a discharge of 2 L min-1 was used to investigate soil detachment from the farms. The soils were coarse texture (having 56-75% sand) and rocky (having 22-57%) with unstable structure and high infiltration rate. Based on the results, soil detachment decreased with increasing SWC in 6.1, 14.8 and 20.7 % slopes. The highest soil detachment rate (g m-2s-1) in these lands was observed in AD-FC (0.01), AD (0.306) and AD (0.0045), respectively. By increasing SWC, the continuity and stability of soil mass of furrow increased, and runoff occurred mostly as subsurface flow in the rills. Surface runoff as well as the soil particle detachment decreased in the rills. Therefore, in the semi-arid slopes with coarse-grained soil, soil detachment rate decreases with increasing SWC.