Nutrient and sediment removal by switchgrass and cool-season grass filter strips in Central Iowa, USA

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- sea son filter strips consisting of bromegrass (Bromus inermis), timothy (Phleu m pratense) and fescue (Festuca spp.) in reducing sediment, nitrogen and ph osphorus 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, s ix each, in the switchgrass and cool- season grass strips, were laid out on Coland soil, having an average slope of 3%. Plots received simulated rainf all of 5.1 cm hr(-1) intensity and simulated runoff containing known quanti ties of sediment and nutrients. Three runon samples, each integrated over 1 5 minutes, and nine runoff samples, each integrated over five minutes, were collected from each plot and analyzed for sediment, total-N, NO3--N, total -P and PO4--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 re moved 46% of total-N, 42% of NO3--N, 52% of total-P, and 43% of PO4--P; and the 3 m filter strips removed 28% of total-N, 25% of NO3--N, 37% of total- P and 34% of PO4--P. Differences between 6 m and 3 m filter strips were sig nificant (P < 0.05) for sediment and nutrient removal. Switchgrass filter s trips removed significantly more total-N, NO3--N, total-P and PO4--P than c ool-season grass filter strips (P < 0.05).