Copper retention from runoff by switchgrass and tall fescue filter strips

ABSTRACT:

Vegetative filter strips are recommended to reduce the load of agricultural chemicals in surface runoff. Quantitative data however, is still needed on the performance of various grass species in filter strips and their effectiveness under different runoff flow rates. A study was conducted to compare the effectiveness of switchgrass (Panicum virgatum L.) and tall fescue (Festuca arundinacea Schreb.) filter strips in removing dissolved copper pesticide from runoff flowing at 2.7 L (0.7 gallon min⁻¹) or 6 L (1.6 gallon min⁻¹) over 0.9 m (3 ft) soil surface area. Runoff was simulated by applying 82-L (22 gallon) solutions containing 6.9 mg L⁻¹ (6.9 ppm) Copper (Cu) on aluminum tilted-beds set at 3% slope, filled with Bojac soil, and planted to switchgrass or tall fescue. The total infiltrated (leached plus retained) expressed as percent of applied was 21% for soil beds having no grass, 33% for switchgrass beds, and 28% for tall fescue beds at 6.0 L min⁻¹ (1.6 gallon min⁻¹) flow rate. At the slow flow rate (2.7 L min⁻¹, 0.7 gallon min⁻¹), 77%, 97% and 100% of the applied runon infiltrated in no grass, switchgrass and tall fescue beds, respectively. About 60% of the applied Cu was removed by both grasses from runoff at 6.0 L min⁻¹ (1.6 gallon min⁻¹) flow rate whereas at the slow flow rate, grasses helped remove all the applied Cu. Average concentration of Cu in surface runoff from all beds was 3.3 mg L⁻¹ (3.3 ppm) whereas for leachate samples it was 0.2 mg L⁻¹ (0.2 ppm). Adsorption to soil appeared to be the primary mechanism of removal of Cu from overland flow and leachate. When runoff moved at 2.7 L min⁻¹ [0.7 gallon min⁻¹) in the tall fescue filter strips, greater amounts of Cu were retained in the up-slope one third of the filter strips. This indicates that a relatively small tall fescue filter strip would be adequate to remove Cu in areas where runoff is expected to move at slow flow rate. The grass filter strips reduced dissolved Cu in runoff by increasing its infiltration and its retention by soil.