Bioenergy for Cattle and Cars: A Switchgrass Production System that Engages Cattle Producers

Published in Agron. J. 105:960–966 (2013) doi:10.2134/agronj2012.0384 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. U the Energy Independence and Security Act of 2007, United States renewable fuel standards required the production of 60.5 gigaliters of ethanol from cellulosic biomass feedstocks by the year 2022 (BRBD, 2008). Early research sponsored by the United States Department of Energy in the 1990s identified switchgrass (Panicum virgatum L.) as a primary next generation cellulosic feedstock that could help the United States achieve its cellulosic ethanol production goal. Switchgrass was identified as a candidate due to its high biomass potential, perennial life-form, adaptability to marginal soils and soil carbon sequestration potential (Frank et al., 2004; McLaughlin and Kszos, 2005; Vogel and Mitchell, 2008; Vogel, 2004). Lowland switchgrass ecotypes (e.g., Alamo variety) have been identified as ideal feedstocks for the southern Great Plains due to their adaptability to the region’s growing conditions (Cassida et al., 2005; Fike et al., 2006; Stroup et al., 2003). Currently, switchgrass lacks a marketable bioenergy feedstock value, which prevents widespread adoption by farmers (Epplin, 2009; Epplin and Haque, 2011; Schnepf, 2010; Smith, 2009). In addition, investors are reluctant to invest in large-scale biorefineries in regions that do not have an established feedstock base (Schnepf, 2010; Yacobucci and Schnepf, 2007). This issue raises the question as to whether or not switchgrass can be incorporated into existing production systems common to the region to encourage investment into large-scale biorefineries. Production of winter pasture and grazing beef stocker cattle on cool-season pastures is one of the primary agricultural production systems in the southern Great Plains (Taylor et al., 2010). The stocker cattle industry is characterized by the development of young, lightweight calves on forage-based diets before placement in feedlots or being returned to the farm and ranch (Schmitz et al., 2003). According to the Economic Research Service (2010), the United States beef cattle industry produces about 40 million feeder cattle annually, of which approximately 14 million have been classified as stockers. Many of these stocker cattle are transported into the southern Great Plains to graze coolseason, annual forages such as cereal rye (Secale cereale L.) and wheat (Triticum aestivum L.) Traditionally, these forages are grazed by stocker cattle from November through April (Hossain et al., 2004; Lang and Broome, 2002), at which time heifers are returned to the farm to potentially replace steers for breeding and steers are transitioned to the finishing stages of production using grain-based diets (Hossain et al., 2004; Schmitz et al., 2003). Recent trends in grain and feeder cattle markets indicate that beef cattle producers face increased pressure to achieve greater livestock gains on forage-based diets before being shipped to feedyards (Peel, 2012). Stocker cattle producers, therefore, are seeking forage systems that allow them to extend their traditional pasturebased grazing seasons (McCollum et al., 1990). ABSTRACT Switchgrass (Panicum virgatum L.) produced for bioenergy is expected to compete with land resources used for stocker cattle (Bos taurus) grazing in the southern Great Plains. The objective was to determine the effect of stocking rate on animal performance, biomass yield, and quality. Three stocking rates (light [2.5 steers ha–1], moderate [4.9 steers ha–1], and heavy [7.4 steers ha–1]) and an ungrazed control were randomly assigned to twelve 0.81-ha paddocks in 2008, 2009, and 2010. Animal and biomass responses were analyzed using mixed ANOVA models. Average daily gain (P = 0.05) was 0.83, 1.04 and 1.05 kg head (hd)–1 for the light, moderate and heavy stocking rates, respectively. Grazing duration was affected (P < 0.001) by stocking rate treatment, realizing 81, 43, and 28 d of grazing, respectively. Steer grazing days were not different (P = 0.22) between stocking rates treatments, producing 81, 86, and 84 d ha–1, respectively. Total gain by treatment were 167, 215, and 199 kg ha–1, respectively, and were different (P = 0.04). The ungrazed control produced more (P < 0.001) harvested biomass at the end of the growing season (15.3 Mg ha–1) compared to the grazed treatments (10.6, 8.1, and 7.8 Mg ha–1, respectively). Forage quality decreased (P < 0.05) throughout the growing season for all treatments. Results indicate switchgrass has the potential to extend the cool-season grazing season in the region while also allowing for the production of an annual supply of bioenergy feedstock for conversion into biofuel.