Use of Warm-Season Grasses Managed As Bioenergy Crops for Phytoremediation of P in P-Enriched Soils.

Phosphorus management in agricultural systems continues to be a relevant issue of agronomic and environmental importance. The objectives of this study were to i) investigate the potential P-removal capacity of four bioenergy crops [(elephantgrass (Pennisetum purpureum Schum.), sugarcane (Saccharum spp.), switchgrass (Panicum virgatum L.), and stargrass (Cynodon nlemfuensis Vanderyst)] grown on a manure-enriched soil, and ii) examine the impacts of crop P uptake on soil P concentrations and surface groundwater quality. Treatments were distributed in a completely randomized design with four replicates. The greatest dry matter (DM) yields were observed for elephantgrass (average of 46 Mg ha^-1 yr^-1) followed by sugarcane (average of 40 Mg ha^-1 yr^-1). Tissue P concentrations were greater for stargrass (~ 4 g kg^-1) as compared to elephantgrass (3.2 g kg^-1) and sugarcane (1.9 g kg^-1). Elephantgrass showed the greatest cumulative P removal (420 kg P ha^-1 during the 3-yr period). Soil P concentrations in the Ap horizon decreased over time, while an increase in soil P concentration was observed in the Bh horizon. Elephantgrass resulted in the lowest leachate P concentrations (~0.5 mg P L^-1) at 60-cm depth.  Crop species had no effect on leachate P at the 90-cm depth. Growth of elephantgrass as a biofuel feedstock appears to be an effective approach for remediation of excess soil P.