The Charcoal Vision : A Win – Win – Win Scenario for Simultaneously Producing Bioenergy , Permanently Sequestering Carbon , while Improving Soil and Water Quality

178 Agronomy Journa l • Vo lume 10 0 , I s sue 1 • 20 08 Published in Agron. J. 100:178–181 (2008). doi:10.2134/agronj2007.0161 Copyright © 2008 by the American Society of Agronomy, 677 South Segoe 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 twin crises of global climate change and the rapidly approaching inability of oil supplies to meet global energy demand are major social, political, and economic challenges of our time. Th ere is growing scientifi c consensus that climate change is driven by anthropogenic emissions of greenhouse gasses to the atmosphere and that the use of fossil fuels for energy is the dominant source of the emissions (Intergovernmental Panel on Climate Change, 2007). Whether peak global oil production has already occurred or will occur in 30 yr is a subject of intense debate (Witze, 2007). However, fi nite reserves and rapidly increasing demand for oil will inevitably force world economies to abandon oil as the primary source of energy. No single solution to these challenges will likely ever be found; however, described herein is a vision for an integrated agricultural biomass–bioenergy system that could make a signifi cant contribution to the solution to both problems and have the added benefi ts of enhancing soil and water quality. Th e potential for ethanol production from cellulose is generating excitement and is currently the focus of much research and development activity. Th e capacity to produce ethanol from cellulose, using co-crops such as corn and wheat stover and dedicated biomass crops such as hybridpoplars and switchgrass, greatly exceeds our capacity to produce ethanol from grain. Th e USDOE recently announced $385 million in Federal funding to support construction of six second-generation cellulosic biofuel plants that will each process between 700 and 1200 tons of dry biomass per day to produce a total of >130 million gallons of cellulosic ethanol per year (USDOE, 2007). Within 10 yr numerous megabiorefi neries (∼1800 metric tons of dry biomass per day) may be operating in the United States. Th e large size of these plants is envisioned to take advantage of inherent economies of scale. Many agricultural scientists, farmers, and conservationists are concerned about the potential impact of biomass harvesting on soil and water quality. Crop residues, although often referred to as agricultural waste, are in fact a vital component of soil agroecosystems. Crop residues contain substantial amounts of plant nutrients (primarily C, N, K, P, Ca, and Mg), and if crop residues were harvested every year these nutrients would have to be replaced by increased fertilizer use. Many soil organisms utilize crop residues as their primary substrate, and these organisms are responsible for nutrient cycling, building of biogenic soil organic matter, and maintaining levels of soil organic C. Crop residues are critically important for building and maintaining soil structure, which facilitates root penetration and the movement of both air and water in soils. And, crop residues on soil surfaces enhance water infi ltration, which increases available water to growing plants, and decreases the destructive eff ects of raindrop impact and surface runoff , which are the dominant causes of soil erosion. If all aboveground crop residues were removed year after year, the quality of our soils would rapidly deteriorate (Wilhelm et al., 2004). Production agriculture would require more fertilizer, more tillage, and more irrigation water to produce the same crops, and the quality of our ABSTRACT