Effects of antecedent soil moisture on rill erodibility and critical shear stress

Antecedent soil moisture is known to exert a complex, perhaps controversial, effect on rill erodibility and critical shear stress. To understand their dynamic nature as a function of antecedent soil moisture, the rill erodibility and critical shear stress for sandy loam and silty loam soil, representing coarse-grained and fine-grained soil, respectively, were measured using a hydraulic flume under six antecedent soil moisture contents, i.e., 3, 6, 9, 12, 15, and 18%. The results show that antecedent soil moisture had a different effect on critical shear stress and rill erodibility for the two different soil textures. As antecedent soil moisture increased, rill erodibility for the fine-grained soil first increased and then decreased, whereas for coarse-grained soil, rill erodibility exhibited a decreasing pattern. Conversely, as the antecedent soil moisture increased, the critical shear stress decreased first and then increased for the fine-grained soil, but for coarse-grained soil, the critical shear stress decreased after a slight increase. These different patterns can be interpreted by aggregate slaking, capillary force, soil cementation, and water separation. However, when the patterns of critical shear stress and rill erodibility were neglected, the differences in critical shear stress and rill erodibility between the coarse- and fine-grained soils were not statistically significant (P < 0.05). Therefore, indiscriminate treatments of critical shear stress and rill erodibility for different textural soils under changing antecedent soil moisture regimes may cause errors in soil erosion modeling. The relationship between rill erodibility and critical shear stress for coarse- and fine-grained soils could be fitted by a power and a polynomial function, with R2 value of 0.94 and 0.78, respectively. Future work should include additional soil textures to study the influence of soil physical characteristics in combination with antecedent soil moisture on soil erosion.