Fertilizer Recommendations for Switchgrass: Quantifying Economic Effects on Quality and Yield

Fertilizer recommendations for switchgrass depend on its price and fertilizer cost. Different fertilizer rates affect yield and hay quality for first and second cuts. Substituting poultry litter for fertilizer affects breakeven, yield, and quality. Switchgrass hay can compete with traditional hay in cattle rations. Switchgrass (Panicum virgatum L.) is a native, perennial warm‐season grass suited for biomass production for renewable fuels and also fodder on marginal soils. To develop fertilizer recommendations, yield responses to and nutrient removal in harvest biomass associated with five levels of macronutrients of N, P, and K on Leadvale silt loam (fine‐silty, siliceous, semiactive, thermic Typic Fragiudults) with a fragipan at 14 to 97 cm at a mid‐southern US location were examined. Feed quality was assessed using crude protein (CP) and total digestible nutrient (TDN) concentration to assess feasibility in beef cow (Bos taurus) rations. Nitrogen affected economic performance to a larger extent than P and K. Profit‐maximizing K use rivaled that of N use, whereas P use was low and thereby limited sustainable poultry litter application. Hay ranged between 7 and 9% CP and 51% ± 0.5% TDN in response to harvest time and nutrient application rate. Cattle producers would find such hay suitable for maintaining dry cows without need for supplemental feed. Profitability of hay production and fertilizer recommendations varied largely with changes in switchgrass price and fertilizer cost. As such, a supplemental spreadsheet tool was developed for research outreach purposes to provide output price‐ and input cost‐specific fertilizer recommendations for switchgrass hay with attendant quality impacts. Overall, breakeven prices were lower using inexpensive litter in comparison with synthetic fertilizers and ranged from approximately US$40 to US$60 Mg−1 in this study. Therefore, switchgrass hay compared favorably in cost to traditional hay averaging US$126 Mg−1 over the study period.