Evaluation of agricultural sediment load reductions using vegetative filter strips of cool season grasses

Vegetative filter strips for controlling sediment generated from the bare ground (i.e., ground not protected by mulch or plant cover) were studied. Plots consisted of a 4.6-m clean-tilled upslope sediment source area and 12.2-m vegetative filter strip located downslope from the sediment source area. Vegetative filter strips consisted of pure stands of six adapted cool season grasses and two cereal grains. Sediment-laden runoff was transported into the upslope edge of each filter strip. Runoff samples were collected from the lower end of each plot and analyzed for nonflow weighted sediment concentration. The rate of advance of water through each vegetative filter strip was measured. Additional measurements were made to define the plant characteristics of each vegetative filter strip species. In general, planted vegetative filter strips resulted 68% reduction concentration of sediment in initial runoff from a 50-year, 24-hour storm event on prewetted soil. Crested wheatgrass and smooth bromegrass vegetative filter strips reduced water flow velocity an average of 217% compared with the clean-tilled control plot. The length of time that water remained in the vegetative filter strip modestly correlated with average sediment concentration in runoff that was 5.5 g/L and 5.0 g/L, respectively, compared with the control plot, which yielded 16.3 g of sediment/L of runoff. Under dry soil conditions, sediment concentration in runoff from bromegass and crested wheatgrass was reduced by an average of 85% compared with the bare control plot. Length of time for water to advance through the smooth bromegrass and crested wheatgrass vegetative filter strips increased an average of 325% compared with the length of time required to flow through the clean-tilled bare strip.