Runoff Through and Upslope of Contour Switchgrass Hedges

Grass hedges are specialized vegetative buffers effective in trapping sediment, but less is known about their ability to reduce or redirect runoff. Runoff and sediment yield from natural rainfall were measured during 8 yr from 0.1-ha contour-planted plots with and without 1-m-wide switchgrass (Panicum virgatum L.) hedges at their lower ends. Plots had slope lengths of 22 m with a steepness of 5%, were located on silt loam soils near Holly Springs, MS, and were cropped to conventional-tillage corn (Zea mays L.). During the first 4 yr of the study, care was taken to conduct tillage is such a way that no soil was thrown into the grass hedge, while during the last 4 yr of the study, primary disk tillage immediately adjacent to the grass hedges created soil berms that acted as low terraces. Hedges reduced the fraction of rainfall that ran off the plots, and hedges with soil berms reduced runoff even more. The runoff curve number (CN) for a 2-yr return period rainfall event was about 78 for plots with no hedges, 70 for plots with hedges, and 61 for plots with hedges with berms. Without berms, 95% of runoff passed through the hedges. In contrast, with berms most runoff (>85% from runoff events <3 mm d(-1); >55% for events <80 mm d(-1)) flowed upslope of and parallel to the hedges. With or without berms, grass hedges decrease sediment yield by a factor of 0.25 to 0.28.