NUTRIENT AND SEDIMENT REMOVAL BY SWITCHGRASS AND COOL-SEASON GRASS FILTER STRIPS IN CENTRAL IOWA, USA

Abstract

Simulated rainfall and runoff were used to compare the effectiveness of 6 m and 3 m wide filter strips of switchgrass (Panicum virgatum) and cool-season filter strips consisting of bromegrass (Bromus inermis), timothy (Phleum pratense) and fescue (Festuca spp.) in reducing sediment, nitrogen and phosphorus in surface runoff from adjacent crop fields. The 6 m and 3 m wide strips represented 20:1 and 40:1 area ratios, respectively. Twelve plots, six each, in the switchgrass and cool-season grass strips, were laid out on Coland soil, having an average slope of 3%. Plots received simulated rainfall of 5.1 cm hr1 intensity and simulated runoff containing known quantities of sediment and nutrients. Three runon samples, each integrated over 15 minutes, and nine runoff samples, each integrated over five minutes, were collected from each plot and analyzed for sediment, total-N, \({\text{NO}}_{\text{3}}^{\text{ - }} \)-N, total-P and \({\text{PO}}_{\text{4}}^{\text{ - }} \)P. The 6 m wide filter strips removed 77% while the 3 m removed 66% of the incoming sediment from surface runoff. The 6 m filter strips removed 46% of total-N, 42% of \({\text{NO}}_{\text{3}}^{\text{ - }} \)-N, 52% of total-P, and 43% of \({\text{PO}}_{\text{4}}^{\text{ - }} \)-P; and the 3 m filter strips removed 28% of total-N, 25% of \({\text{NO}}_{\text{3}}^{\text{ - }} \)-N, 37% of total-P and 34% of \({\text{PO}}_{\text{4}}^{\text{ - }} \)-P. Differences between 6 m and 3 m filter strips were significant (P < 0.05) for sediment and nutrient removal. Switchgrass filter strips removed significantly more total-N, \({\text{NO}}_{\text{3}}^{\text{ - }} \)-N, total-P and \({\text{PO}}_{\text{4}}^{\text{ - }} \)-P than cool-season grass filter strips (P < 0.05).