Yield and nitrogen management of irrigated switchgrass systems in diverse ecoregions

Published in Agron. J. 105:311–320 (2013) doi:10.2134/agronj2012.0354 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. I in alternative sources of energy has increased in recent years due to increasing prices of petroleum-based fuels, national security concerns in the United States (Kering et al., 2012a), and climate change induced by increasing concentration of greenhouse gases in the atmosphere. Biomass energy crops may provide a viable alternative source of energy (McLaughlin et al., 2002). Potential uses for biomass are electric energy generation through co-fi ring with coal (Tillman, 2000), gas production by thermo-chemical gasifi cation, and biochemical conversion into liquid fuels such as ethanol (Parrish and Fike, 2005). Switchgrass is a perennial warm season C4 grass native to North America, occurring naturally throughout the mainland United States, except California and the Pacifi c Northwest. It is one of the dominant species in the North American tallgrass prairie and can be found in remnant prairies, native grass pastures, and along roadsides. To date it has primarily been used as forage, ground cover, and wildlife refuge (USDANatural Resources Conservation Service. Jimmy Carter Plant Materials Center, 2011). Recently, switchgrass has received considerable attention as one of the most promising energy crops, due to its high yield potential, excellent conservation attributes, good compatibility with conventional agricultural practices, relative ease of establishment, high seed production, adaptability to marginal areas, and high N use effi ciency, becoming a model feedstock for energy production (McLaughlin et al., 1999; McLaughlin and Kszos, 2005). Th e majority of switchgrass research for biomass energy production has been performed in the Midwest and southern United States under rainfed conditions. Switchgrass biomass yields range from as low as 5.5 to as high as 25 Mg ha–1, depending on stand age, varietal selection, N fertilization, precipitation, and harvest management (Heaton et al., 2004; Sanderson et al., 1999). Similar to biomass yields, biomass N concentration and N removal by harvest vary widely. Depending on yield, N fertilization, and harvest management, biomass N concentration range from 1.7 to 14.5 g kg–1 DM and from 28 to 234 kg N ha–1 yr−–1 for N removal by harvest (McLaughlin et al., 1999; Vogel et al., 2002). Nitrogen fertilizer is the main energy input and source of greenhouse gases emissions from switchgrass cultivation (Adler et al., 2007; Schmer et al., 2008), and an important factor in switchgrass biomass yields (Heaton et al., 2004; Stroup et al., 2003). It is therefore critical to understand how switchgrass responds to N fertilization to develop energy effi cient and environmentally benign production systems for biomass energy production. Yield responses to N fertilization are variable and confl icting due to variations in soils, crop management, and climate (Parrish and Fike, 2005). Some have reported limited to no response to N fertilizers (Christian et al., 2002; Garten et al., 2011; Jung and Lal, 2011; Kering et al., 2012b; ABSTRACT