Grass barrier and vegetative filter strip effectiveness in reducing runoff, sediment, nitrogen, and phosphorus losses

Grass barriers may be a potential alternative to vegetative filter strips for reducing sediment and nutrient loss in sheet and concentrated flow erosion. This study evaluates the effectiveness of switchgrass ( Panicum virgatum) barriers, traditional fescue (Festuca arundinacea ) filters strips (FS), and native species filter strips with barriers (Native-FS) for reducing runoff, sediment, nitrogen (N), and phosphorus (P) losses from 1.5- by 16-m plots on a Mexico silt loam (Vertic Aeric Epiaqualfs) under sheet and concentrated flow. Grass barriers (0.7 m long) were established below 1.5- by 8-m long plots (sediment source areas) under continuous cultivated fallow and above 1.5- by 8-m long filter strips (FS). Soil berms treated with anionic polyacrylamide (PAM) at a rate of 9 kg ha−1, and then covered with geo-textile fabric (GF) were used as plot borders. Two treatments had an artificial channel in the source area to simulate concentrated flow erosion. Supplemental inflow rates up to 12.5 L min−1 were added at the top of the plots of the concentrated flow treatments to simulate larger source areas under dormant barriers. Runoff produced from simulated rainfall at 66 mm h−1 was sampled at 1 m above the downslope edge of the sediment source area, and 0.7, 4, and 8 m below the source area to measure sediment, N, and P concentrations with distance. Under sheet flow, barriers and fescue-FS at 0.7 m reduced runoff and sediment loss, but barriers reduced runoff 31% more and sediment 15% more than fescue-FS (P < 0.01). Barriers also reduced organic N, NO₃ -N, NH₄-N, particulate P, and PO₄-P more than fescue-FS (P < 0.01). Native-FS and fescue-FS were equally effective for reducing sediment and nutrient loss. Fescue-FS effectiveness increased with distance but >25% of runoff, ∼94% of sediment, and ∼78% of nutrient loss were reduced after 4 m of FS. A modified equation accounting for the runoff ponding above barriers explained >70% of the variability between measured and predicted values of sediment, organic N, and particulate P transport. Under concentrated flow, active and dormant barriers above fescue reduced runoff 33% more than fescue-FS alone at 0.7 m (P < 0.05). Barriers reduced sediment by 92% but fescue-FS reduced sediment only 72% ( P < 0.01). Fescue-FS reduced only 60% of sediment when the source area was doubled by adding inflow rates, but not in barriers. Barriers reduced more nutrients than fescue-FS except NO₃-N and PO₄-P. PAM and GF reduced soil loss from berms by 99%, indicating that berms can be an economical alternative to steel plate plot borders. Barriers and native-FS can be effective alternatives to fescue-FS for reducing sediment and nutrient loss in sheet and concentrated flow erosion while promoting wildlife habitat. Barriers can improve the fescue-FS performance for controlling sediment and nutrient transport.