Interrill erosion and roughness parameters of vegetation in rangelands

- Interrill erosion and vegetal roughness
- Sheet flow hydraulics
- Drag force in sheet flow

In recent decades, the micro-region of Paraiba state, Brazil, has been undergoing the process of replacing its native coverage by crops, mainly pastures for grazing. This land use change has led to the detachment of soil due to the water erosion. Thus, this research had the merit of analyzing the hydraulic roughness parameters generated by pasture emergent vegetation in field condition under interrill erosion. This study was conducted in a randomized block with 4 treatments and 5 replicates, totaling 20 experimental plots. The treatments comprised different slopes (15%, 25%, 35% and 45%) in an Ultisol. The mean flow velocity and the rate of infiltration in the pasture varied significantly with the increase in slope, contributing to increasing erosion rates until 35% slope. For the slope equal to 45%, the largest soil loss was not observed, chiefly because the crop covers offset the effects generated by the increase in the slope and also due to the remotion of surface horizon (A horizon) which was removed by previous water erosion, which now acted directly on the B horizon. The vegetation drag coefficient (CD′) of the pasture exhibited an increase when occurred a reduction of turbulent flow between plants. In the condition of increasing in flow depth (h) there was a greater energy flux between the mass of water and the plant structure of Brachiaria decumbens that resulted in the decrease of the vegetation resistance force (Fdrag).