Switchgrass Response to Cutting Frequency and Biosolids Amendment: Biomass Yield, Feedstock Quality, and Theoretical Ethanol Yield Xiao-Jun Allen Liu & John H. Fike & John M. Galbraith & Wonae B. Fike Published online: 13 April 2014 # Springer Science+Business Media New York 2014 Abstract Biofuel crops have relatively low economic value, and potential to grow them with low-cost inputs is essential for economic viability. Use of biosolids as a fertility source has not been explored at the field scale for switchgrass (Panicum virgatum L.), a potential bioenergy crop. This study tested harvest management and biosolids rate effects on switchgrass production, quality, and theoretical ethanol yield in Virginia, USA. Switchgrass (cv. “Cave-in-Rock”) was annually cut once (winter) or twice (summer and winter) for 2 years. Bio- solids were applied once at 0, 77, and 154 kg N ha -1 in May 2011; urea was applied once at 146 kg N ha -1 for comparison. Feedstock yield and quality parameters (neutral and acid detergent fibers, cellulose, hemicellulose, lignin, and ash) were measured and used to compute theoretical ethanol po- tential (TEP) and theoretical ethanol yield (TEY). Cutting twice per season produced greater biomass yields than cutting once (6.6 vs 5.4 Mg ha -1 ) in 2011 but not in 2012. Cutting once per season produced feedstock with greater TEP (513 vs 433 L Mg -1 ) and TEY (2,980 vs 2,680 L ha -1 ) in both years. Biosolids and urea increased biomass yields by 11 % (0.6 Mg ha -1 ) and TEY by 13 % (352 L Mg -1 ), but both decreased TEP by 1 % (7.1 L Mg -1 biomass). Cutting once per season is advantageous in producing more TEY given comparable biomass yield and superior feedstock quality. Biosolids were a suitable alternate N source and could boost biomass and biofuel production while reducing input costs in switchgrass-based bioenergy systems. Keywords Bioenergy crop . Nitrogen fertilization . Biofuel quality . Feedstock cellulose . Grass cell wall . Organic fertilizer Introduction As a perennial grass and bioenergy crop, switchgrass has potential to meet agronomic, environmental, and sustainable development requirements for biofuel production [1, 2]. The crop has high yield potential and is adapted to erodible and low-fertility marginal lands [3, 4]. However, because yields will likely be lower on marginal lands—often even with significant nutrient inputs—and because bioenergy crops will likely be low-value commodities, improving harvest manage- ment practices [5, 6] and reducing cost of inputs such as nutrients [7] will be essential for system profitability. Sustainable harvest management practices are critical for optimizing switchgrass yield. Previous studies, despite being location-, cultivar-, or climate- dependent, have shown that multiple harvests can increase switchgrass yields about 15 % [8, 9]. However, multiple cuttings per season also can reduce switchgrass yields under stressful environmental conditions, particularly in dry years or on excessively drained soils [10]. Harvest management also affects feedstock quality parameters (e.g., cellulose, hemicellulose, lignin, and ash), which in turn affect biomass-to-biofuel conversion efficiencies [2, 11, 12]. When cut in late fall, switchgrass has greater fiber and lignin and lower mineral concentrations relative to harvests earlier in the season [13, 14]. Although harvesting in late summer or early fall may maximize yields [2, 15], earlier harvests can result in lower feedstock quality and increased costs associat- ed with greater nutrient removal than later harvests [16]. Thus, X.<J. A. Liu (*) Department of Biological Sciences and Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ 86011, USA e-mail: xj.allen.liu@gmail.com URL: http://xjaliu.weebly.com J. H. Fike : J. M. Galbraith : W. B. Fike Department of Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA Bioenerg. Res. (2014) 7:1191–1200 DOI 10.1007/s12155-014-9454-4