Effects of harvest frequency and biosolids application on switchgrass yield, feedstock quality, and theoretical ethanol yield XIAO-JUN ALLEN LIU* † , JOHN H. FIKE ‡ , JOHN M. GALBRAITH ‡ , WONAE B. FIKE ‡ , DAVID J. PARRISH ‡ , GREGORY K. EVANYLO ‡ and BRIAN D. STRAHM § *Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011, USA, †Ecosystem Science & Society Center, Northern Arizona University, Flagstaff, AZ 86011, USA, ‡Department of Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA, §Department of Forest Resources and Environmental Conservation, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA Abstract Sustainable development of a bioenergy industry will require low-cost, high-yielding biomass feedstock of desir- able quality. Switchgrass (Panicum virgatum L.) is one of the primary feedstock candidates in North America, but the potential to grow this biomass crop using fertility from biosolids has not been fully explored. The objective of this study was to examine the effects of harvest frequency and biosolids application on switchgrass in Virginia, USA. ‘Cave-in-Rock’ switchgrass from well-established plots was cut once (November) or twice (July and November) per year between 2010 and 2012. Class A biosolids were applied once at rates of 0, 153, 306, and 459 kg N ha 1 in May 2010. Biomass yield, neutral and acid detergent fiber, cellulose, hemicellulose, lignin, and ash were determined. Theoretical ethanol potential (TEP, l ethanol Mg 1 biomass) and yield (TEY, l etha- nol ha 1 ) were calculated based on cellulose and hemicellulose concentrations. Cutting twice per season pro- duced greater biomass yields than one cutting (11.7 vs. 9.8 Mg ha 1 ) in 2011, but no differences were observed in other years. Cutting once produced feedstock with greater TEP (478 vs. 438 l Mg 1 ), but no differences in TEY between cutting frequencies. Biosolids applied at 153, 306, and 459 kg N ha 1 increased biomass yields by 25%, 37%, and 46%, and TEY by 25%, 34%, and 42%, respectively. Biosolids had inconsistent effects on feedstock quality and TEP. A single, end-of-season harvest likely will be preferred based on apparent advantages in feedstock quality. Biosolids can serve as an effective alternative to N fertilizer in switchgrass-to-energy systems. Keywords: ash, bioenergy crop, biofuel quality, biomass, cellulose, hemicellulose, lignin, nitrogen Received 17 May 2013; accepted 9 July 2013 Introduction Switchgrass is a perennial C 4 grass considered promis- ing for biofuel production given its many desirable attri- butes, including productivity on marginal land (Parrish & Fike, 2005). The main agronomic costs associated with switchgrass production for energy systems include N fertilization and harvest management (Vogel et al., 2002), and these factors will have important impacts on logistics, another important cost center for bioenergy production systems (Cundiff et al., 2009). Thus, under- standing the effects of agricultural practices (e.g., N fertilization sources and application rates, number of harvest events) on yield and feedstock quality is a key requirement for optimizing productivity and economics of switchgrass biomass production systems. Generally, the major nutrient requirement of switch- grass is N (Trocsanyi et al., 2009; Guretzky et al., 2011), and the amount needed largely depends on the produc- tivity of cultivars, yield potential at specific locations, and harvest management practices. For example, low- land and upland switchgrass yields ranged from 10.4 to 19.1 Mg ha 1 in response to 50 kg N ha 1 in the upper southeastern USA (Fike et al., 2006b). Optimum N fertil- ization rates of the lowland switchgrass cultivar ‘Alamo’ were 122 kg N ha 1 in Alabama (McLaughlin & Kszos, 2005) and 168 kg N ha 1 in Texas (Muir et al., 2001). Other studies suggest that switchgrass yields increase in response to N rates at levels between 56 and 120 kg N ha 1 before plateauing at higher rates (Gunderson et al., 2007; Lemus et al., 2008a; Haque et al., 2009). Most switchgrass N-response studies have been con- ducted using industrial fertilizers. However, minimiz- ing N input costs while maintaining productivity will be important for the profitability of switchgrass Correspondence: John H. Fike, tel. + 540 231 8654, fax + 540 231 3431, e-mail: jfike@vt.edu © 2013 John Wiley & Sons Ltd 1 GCB Bioenergy (2013), doi: 10.1111/gcbb.12124