Fertilizer recommendations for switchgrass: Quantifying economic effects on quality and yield

Authors: POPP, MICHAEL - University Of Arkansas; Ashworth, Amanda; Moore, Philip; Owens, Phillip; DOUGLAS, JOEL - Natural Resources Conservation Service (NRCS, USDA); Pote, Daniel; JACOBS, ALAYANA - Natural Resources Conservation Service (NRCS, USDA); LINDSAY, KAREN - Natural Resources Conservation Service (NRCS, USDA)

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/12/2018
Publication Date: 8/2/2018
Citation: Popp, M.P., Ashworth, A.J., Moore Jr, P.A., Owens, P.R., Douglas, J.L., Pote, D.H., Jacobs, A., Lindsay, K. 2018. Fertilizer recommendations for switchgrass: Quantifying economic effects on quality and yield. Agronomy Journal. 110(5):1854-1861. https://doi.org/10.2134/agronj2018.04.0273.
DOI: https://doi.org/10.2134/agronj2018.04.0273

Interpretive Summary: Switchgrass, a native grass that grows well under low nutrients and drought conditions, may be used in cattle operations for supplying potentially low-cost hay. Although, little information exists on break-even prices at various fertilizer rates for current hay prices for this forage crop. The purpose of this work, therefore, is to gain greater insight into switchgrass yield response to nutrients (both fertilizers and poultry litter) and to verify if fertilizer additions are economical. Researchers developed a decision support tool (entitled Energy Crop Analysis & Planning) to assist hay and cattle producers with determining what hay quality to expect and to what extent hay cost savings would be offset by added feed supplement costs. This study found that profitability of hay production, as well as fertilizer and poultry litter recommended applications varied largely with changes in switchgrass market prices and fertilizer costs. Based on average hay prices since 2008, the use of poultry litter in place of synthetic fertilizers greatly improved on-farm profitability. Overall, integrating switchgrass into forage management systems may allow producers increased flexibility to respond to variations in biomass, forage, and livestock markets.

Technical Abstract: Switchgrass (Panicum virgatum L.) is a native, perennial warm season grass that is suited for biomass production for conversion to renewable fuels as well as feed production on marginal soils. Yield responses to macro nutrients of N, P and K, have shown N to be the major driver for capturing yield potential. On the other hand, P removal in harvested biomass tends to be minimal whereas K removal rivals that of N removal in terms of quantity. This nutrient response study used data from field trials conducted on marginal soil to develop yield curves that assisted with forming fertilizer recommendations on the basis of yield response and macro nutrient removal in harvested material that is destined for feed in beef cattle (Bos taurus L.) rations. Results show that harvest in early June and late July provided hay with crude protein concentrations ranging between 7 and 9% and total digestible nutrient concentration near 51%. Cattle producers would find such hay suitable for maintaining dry cows without need for supplemental feed to raise primarily CP concentration in the feed ration. Profitability of hay production as well as fertilizer and poultry litter application rate recommendations varied largely with changes in switchgrass price and fertilizer cost. A supplemental spreadsheet file was developed to provide flexibility for making fertilizer recommendations for growing switchgrass for hay. The spreadsheet showed breakeven prices ranging from approximately $40 to $60 Mg-1 that compared favorably to traditional hay averaging $126 Mg-1 over the study period.