Abating endosulfan from runoff using vegetative filter strips: the importance of plant species and flow rate

Vegetative filter strips (VFS) can reduce the load of agricultural chemicals from runoff. Despite their heavy promotion, quantitative data is lacking on the performance of different grass species in filter strips and their effectiveness under different flow rates. The purpose of this study was to compare and determine the effectiveness of switchgrass (Panicum virgatum L.) and tall fescue (Festuca arundinacea Schreb) filter strips in removing dissolved endosulfan from runoff flowing at different rates. Aluminum tilted beds filled with Bojac soil, set at 3% slope and planted to switchgrass or tall fescue or bare soil were used. Runoff was simulated by applying runon containing endosulfan (mixture of (alpha)and (beta)isomers) at the up-slope section of the beds at 2.7 or 6 l min^-1 over 0.9 m wide soil surface. Results indicate no preferential removal of one endosulfan isomer over the other. Total endosulfan removed ranged from 98 to 100% (percent of applied) for the 2.7 l min^-1 runon application rate, and 39-54% for the 6.0 l min^-1 runon application rate. All the applied runon infiltrated tall fescue planted beds at the slower flow rate whereas at the faster flow rate, only 29% penetrated the fescue bed. Endosulfan was filtered out of the surface runoff and leachate collected. From overland flow, concentrations of endosulfan were reduced by about 6080% at the 2.7 l min^-1 application rate and by 27-39% at the 6.0 l min^-1 runon application rate. Adsorption to soil is the primary mechanism for removal of endosulfan from overland flow and from leachate. The effectiveness of the grasses were more important when the runon moves fast. At both flow rates, more endosulfan adsorbed to the soil in the first 0-67 cm section of the beds than from the down slope (67-133 or 133-200 cm) sections and adsorbed to the soil in the top 0-10 cm depth. Results indicate that most of the insecticide was removed in the first one-third of the filter strip.