Small Grain Residue Management Effects on Soil Organic Carbon: A Literature Review

Published in Agron. J. 103:247–252 (2011) Published online 9 Dec 2010 doi:10.2134/agronj2010.0147s Copyright © 2011 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. T immediate and long-term effects of removing aboveground crop residues from fi elds on soil properties and crop productivity have major implications for the sustainability of agriculture in some regions. Historically much of the crop residue was returned to the soil system in the fi eld. Several changes and potential changes in straw management have led to these concerns including removal of straw from grain fi elds for animal bedding and feed, and the potential development of cellulosic-based ethanol production (Johnson et al., 2006; Wilhelm et al., 2007). Increased animal populations in some areas have resulted in more removal of small-grain residues from fi elds for use as feed and bedding. For example, in an eight-county area of southern Idaho, the dairy population has increased by 258,500 cows from 1990 to 2006. Use of crop residue as a source for biofuel has received much attention in recent years (USDA-NASS, 2010). A series of policies promoted the increased production of biofuels, including the 2000 Biomass Research and Development Act, the 2006 Energy Policy Act, the 2007 Energy Independence and Security Act (mandated a production of 515.6 billion L of biofuels by 2022) and the 2002 and 2003 Farm Bill (Biomass Research and Development Initiative, 2008). It is likely that future policies will continue to consider crop residues as sources of energy. Ethanol derived from cellulose is currently the leading candidate of alternative fuel to replace a large portion of the U.S. petroleum-derived fuels (Perlack et al., 2005). Th e U.S. Departments of Energy and Agriculture estimate 30% of the current U.S. petroleum consumption could be replaced by 1.18 billion Mg of biomass without large negative eff ects on land-based cropping systems (Perlack et al., 2005). Corn (Zea mays L.) residue has been determined to be the major source of cellulose (Perlack et al., 2005). Straw produced from small grains such as wheat and barley can also be a source of cellulose for ethanol production (Nelson, 2002; Johnson et al., 2007). Table 1 shows selected statistics of wheat and barley production in the United States. Th e average estimated total annual aboveground biomass from all wheat and barley production from 2001 to 2006 in the United States totals 64.3 Tg (dry weight basis) (USDA, NASS). Total wheat and barley aboveground biomass represents 25.3% of the stover produced from corn production in the United States in 2000 (253.7 Tg) (Wilhelm et al., 2004). However, under conservation tillage practices, maintaining a base amount of residue will be required to help prevent excessive soil erosion (Johnson et al., 2006; Nelson, 2002). Th e management of crop residues in cropping systems is becoming an important issue in many areas of the United States. Crop residue nutrient cycling in soils is important because residues are a major source of nutrients (N, P, and K) and organic carbon (OC) to soils. A plethora of reported research demonstrates the role of SOC in the plant/soil system. Organic C positively impacts soil ABSTRACT Impact of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) straw removal from fi elds on soil organic carbon (SOC) is a concern. Increased animal populations and potential development of cellulosic ethanol production could increase the removal of straw from fi elds. Th is paper focuses on the eff ects of wheat and barley straw removal on SOC in irrigated production systems, and related the results to estimates of the minimum straw carbon inputs required to maintain soil organic carbon (MSC) from rain-fed systems. Six studies compared SOC changes with time in irrigated systems in which wheat straw was removed or retained. Th ese studies indicated that SOC did not decline when residues were removed. Apparently belowground biomass is supplying C to irrigated soils at a rate suffi cient to maintain SOC with time. However, under rain-fed systems, returning residue to the soil was required to maintain SOC. Estimates of MSC were obtained from nine rain-fed wheat system studies. Averaged across all rain-fed MSC values, 4.14 Mg more straw ha–1 was required to maintain SOC in rain-fed than in irrigated systems. Presently, the rain-fed based MSC values are the best information available to evaluating residue removal eff ects but caution should be used in applying these in irrigated systems. Th e results from this limited number of irrigated studies suggest that rainfed estimates of MSC will overestimate the MSC in irrigated systems and underestimate the available irrigated straw resources. Th ere is need to evaluate the eff ect of residue removal on SOC for diverse irrigated systems.