Switchgrass (Panicum virgatum L.) is a high-yielding grass crop that may be grown on far less fertile soil than maize ( Zea mays L.), thus eliminating the need to take highly productive fields out of food production. A key question for biofuels production is successful and sustainable yields on marginal lands with minimal nutrient inputs. The objectives of this study was to 1) examine the land capability impact on switchgrass yield and biomass composition compared to maize and alfalfa (Medicago sativa L.); 2) examine the role of P and K soil test levels and tissue concentrations on switchgrass yield and composition. ‘Shawnee’ switchgrass was seeded in April 2007 into alfalfa plots with known differences in agronomic performance (High, Medium High, Medium, Medium Low, Low, and Very Low). Alfalfa yield and persistence was measured on these plots from 1997 to 2004. Alfalfa stands were killed with herbicide and no-til maize yield was assessed on these plots in 2006. Switchgrass biomass was harvested in August 2008, and 2009, and October 2010. Yields of maize and alfalfa were correlated (R2=0.041) across plots with varying agronomic performance. Yields of switchgrass were not associated with maize grain/stover yields or alfalfa forage yields in 2004. Plots deemed as marginal for alfalfa yield also limited maize biomass production, but not that of switchgrass. Trends in tissue P and K concentration reflected the historical fertilizer applications, but tissue and soil test P and K levels could not be associated with biomass yield. Soil test P and K and tissue P and K concentrations were well described by linear-plateau models. The Oct. 2010 harvest decreased tissue P by more than 15% and tissue K by more than 60% as compared with the Aug. harvest of 2008 and 2009. Tissue P and K concentrations, and not biomass yield, were the primary factors influencing P and K removal rate. The top and bottom tissue K-producing groups were significantly different among yields all three years with the low K group producing higher yield than the high K group in 2008 and 2009. Lignocellulosic concentrations were not greatly affected by P and K; however, lignocellulose in Oct. harvest compared to Aug. did increase. Our initial results suggest levels of soil P and K that limit alfalfa and maize productivity do not reduce biomass yield of switchgrass, or alter lignocellulose concentrations.
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