Roles of the stolon and erect grass species in surface-subsurface flow generation and red soil loss

Grass planting is an important and typical measure for soil and water conservation, while the roles of stolon and erect grass species in affecting surface-subsurface flow and soil erosion processes are little understood. Experimental plots (2 m x 0.5 m x 0.5 m) using red soil with two rainfall intensities (60 and 120 mm h(-1)) and grass coverage (30 % and 70 %) were conducted in laboratory rainfall simulation experiments. Two common and endemic stolon (Eremochloa ophiuroides) and erect (Lolium perenne) grass species were selected due to their fast growth, power adaptability, and wide application in reducing runoff and soil loss; and the bare soil plot was set up as the control. The results showed that bare plot had the highest mean surface flow coefficient (73.5 %), and then were L. perenne (57.1 %) and E. ophiuroides (44.9 %). The mean subsurface flow coefficients were found in order of E. ophiuroides (25.7 %), L. perenne (13.0 %) and bare plot (7.2 %). The role of stolon grass rather than erect grass in reducing surface flow but improving subsurface flow led to lower surface flow hydraulic characteristics such as flow velocity, Reynolds number, Darcy-Weisbach coefficient and Manning friction coefficient, and hydrodynamic characteristics like flow shear stress and stream power. Furthermore, the stolon grass generated the lowest soil loss rate (0.8 g m(-2) min(-1)), while the values on erect grass and bare plot were 2.5 and 10.7 g m(-2) min(-1 ), respectively. The indicator of eroded sediment median size also proved the higher efficiency of stolon grass in soil loss control, with values of 31.8, 58.6 and 69.6 mu m on stolon grass, erect grass and bare plots, respectively. The lower soil loss on stolon grass cover plot was attributed to the lower surface flow and hydraulic-hydrodynamic characteristics. The stolon grass was more sensitive to the coverage and rainfall intensity, which was explained by the higher flow and sediment trapping capability (2.2 similar to 4.4 times) under lower coverage and rainfall intensity than erect grass, even under high rainfall intensity (1.1 similar to 3.2 times). The stolon grass played more beneficial roles in soil and water conservation than erect grass, which was closely related to above-ground and under-ground parts of grass. This study can provide a better understanding of the roles of stolon and erect grass species for soil and water conservation and management practices.