Switchgrass Winter Yield, Year‐Round Elemental Concentrations, and Associated Soil Nutrients in a Zero Input Environment

Published in Agron. J. 105:463–470 (2013) doi:10.2134/agronj2012.0286 Available freely online through the author-supported open access option. Copyright © 2013 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. S is a warm-season perennial grass native to North America. It is considered a leading candidate for deployment as a cellulosic biomass feedstock crop for bioenergy production (U.S. Department of Energy, 2011). Th e species has high potential to be cultivated as a renewable biofuels feedstock source on marginal land unsuited for traditional cultivated grain and forage crops (Parrish and Fike, 2005). Switchgrass is comprised of two major ecotypes designated “lowland” and “upland” based on edaphic adaptation and plant morphology. Native stands of the lowland ecotype occur on alluvial soils while native stands of the upland ecotype are typically found on drier and less fertile nonalluvial soils. Th e lowland ecotype is naturally distributed in the south-central and southeastern United States to about 40° N latitude while the upland ecotype is distributed throughout the expanse of U.S. switchgrass adaptation. Plants of the lowland ecotype are typically much larger than those of the upland ecotype, thereby having greater biomass production potential in suitable growth environments. Deployment of switchgrass as a bioenergy feedstock crop in the south-central and southeastern United States would likely heavily use lowland cultivars because of their greater biomass production potential compared to upland cultivars. Harvest timing is an important consideration in switchgrass production management as it aff ects biomass yield, chemical composition, harvesting cost, and stand persistence. Sanderson et al. (1999) reported that maximum biomass yield of lowland switchgrass was achieved in Texas with one seasonal autumn harvest completed by mid-September. Th ey further noted total yield was reduced by 12 to 19% depending on locations when the one seasonal harvest was taken in November compared with September. However, delaying the harvest past October in a onecut system can help maximize switchgrass biomass production the next year (Sanderson et al., 1999). Casler and Boe (2003) measured the eff ects of a single seasonal harvest of six upland switchgrass cultivars in Wisconsin and South Dakota during August, September, and October. Th ey reported that an August harvest produced the largest biomass yield in the fi rst year, but proved detrimental to biomass yield and stand persistence by the third year of the study. Th ey further indicated that an October harvest produced the greatest biomass yields over a 4-yr period. Parrish et al. (1997) reported decreased biomass yields associated with delaying autumn harvest of lowland switchgrass in Virginia. Th e decrease in biomass yield associated with delayed autumn harvest has been attributed partially to the remobilization and translocation of C and N reserve compounds from aboveground biomass to regenerative crown structures and underground roots (Parrish et al., 1997; Sanderson et al., 1999). Leaf loss near and aft er the end of the growing season is also thought to contribute to biomass yield reduction (Parrish et al., 1997; Sanderson et al., 1999). Although early fall harvest is recommended (Sanderson et al., 1999), a wider window extending harvest into or through winter months would alleviate potential problems associated with the much shorter early ABSTRACT Th e maximum biomass yield of switchgrass (Panicum virgatum L.) usually is achieved with one seasonal autumn harvest. However, information is limited on the infl uences of winter harvesting on annual biomass yield and on quality parameters impacting conversion into bioethanol. Accordingly, the objectives of this study were to assess: (i) yield of standing fi eld cured biomass at monthly intervals through winter, (ii) year-round elemental composition of biomass, and (iii) associated year-round soil nutrient status. An unfertilized 'Kanlow' switchgrass planting established in 1998 was used for this study conducted from November 2007 to October 2010. Th e experimental treatment was monthly harvest from November to the following March and year-round monthly sampling of biomass (except April) and soil for chemical analyses. Th e 3-yr mean dry matter yield of winter harvests was 5.94Mg ha–1, ranging from 3.88 Mg ha–1 in the winter of 2007–2008 to 7.55 Mg ha–1 in 2009–2010. Monthly biomass yield diff erences were signifi cant in Years 1 and 3 but not in Year 2. Concentrations of biomass elements and soil nutrients changed with various degrees over the 3 yr. Concentrations of ash, cell wall components, and mineral nutrients, except P, K, and S, did not change appreciably across winter months. Early winter harvests resulted in less yield loss compared to late winter harvests. Th ese fi ndings will be valuable in harvest management for switchgrass biomass production.