Evaluating the Impacts of Bioenergy Crops On Soil and Water Resources.

Despite the increased importance of bioenergy crops as a renewable energy alternative, limited information is available relative to the effects of biomass removal for biofuel on soil and water resources. The objective of this study was to investigate the impacts of bioenergy cropping on soil test P and leachate P concentrations in a manure-impacted Spodosol. Treatments consisted of four crops [(elephantgrass (Pennisetum purpureu), sugarcane (Saccharum officinarum), switchgrass (Panicum virgatum), and stargrass (Cynodon nluemfuensis)] cultivated on a commercial dairy farm that had been continuously grazed for over 50 yr. Forage was periodically harvested to determine DM yields and tissue N and P concentrations. Plots received 80 kg N ha^-1 after every harvest. Soil samples were collected annually from Ap, E, and Bh horizons. Two suction lysimeters were installed at 60 and 90 cm depth to monitor P concentrations above and below the Bh horizon, respectively. Dry matter yields varied considerably among the various species. Elephantgrass and sugarcane yielded significantly more than the other species tested. The greatest P uptake and P removal values were observed in the elephantgrass plots. Soil P concentrations in the Ap horizon were reduced in response to P uptake, however no differences were observed in the E and Bh horizons. No differences in P concentrations in the groundwater were observed among the treatments, possibly due the short duration of the study. Despite some limitations, such as the need for high N rates, perennial bioenergy crops can be a feasible alternative to reduce the environmental risks associated with soil P accumulation in manure-impacted soils.