Flow velocity on cultivated soil slope with wheat straw incorporation

Water flow velocity is of great importance in quantifying overland water flow hydrodynamics, related to rainfall infiltration, runoff energy, and soil erosion. Mixing the straw into the cultivated soil can change its physical properties and in turn affect the velocity of water flow. Laboratory investigations were made to measure the velocities of rainfall runoff water flow under four incorporation rates (0, 2, 4 and 8 ton/ha), three rainfall intensities (80, 120 and 160 mm/h) and three slope gradients (10, 15 and 20 degrees), on straw incorporation soil slopes, at slope distances of 5, 6 and 7 m from the top end of the slope, using an electrolyte tracing system. The results show that the flow velocity decreased exponentially with straw incorporation rate. The mean flow velocity ranged from 0.17 to 0.23 m/s over the bare soil slope, while the mean flow velocity ranged from 0.10 to 0.17 m/s, 0.09 to 0.13 m/s, and 0.06 to 0.11 m/s over the soil slopes with straw incorporation rates of 2, 4, 8 t/ha respectively. The 2, 4 and 8 t/ha straw incorporation rates reduced flow velocities by 28.44%, 44.09% and 55.56%, respectively. Higher rainfall intensity and slope gradient caused increase in flow velocity. There was no significant difference between the two adjacent rainfall intensities and slope gradients. A nonlinear multiple regression model was used to fit the measured velocities, which predicts well the effect of straw incorporation rate, rainfall intensity, and slope gradient. Increase in straw application rate had a good effect on reducing the flow velocity which may influence soil erosion and sediment delivery. Velocity over soil slope with straw incorporation can help interpret soil erosion and sediment transportation.