SSSAJ: Volume 74: Number 4 • July–August 2010 1259 Soil Sci. Soc. Am. J. 74:1259–1270 Published online 2 June 2010 doi:10.2136/sssaj2009.0115 Received 20 Mar. 2009. *Corresponding author (jdeenik@hawaii.edu). © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA 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. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Charcoal Volatile Matter Content Influences Plant Growth and Soil Nitrogen Transformations Soil Fertility & Plant Nutrition C harcoal byproducts from the pyrolytic conversion of biomass to biofuels have the potential to address two growing global issues: climate change and the degradation of agricultural soils. As an alternative to the C offset due to the replacement of fossil fuels with renewable biofuels, charcoal used as a soil amend- ment is, first, an attractive alternative for mitigating the negative effects of green- house gas emissions via long-term C sequestration and, second, a promising ap- proach to improving soil quality, crop productivity, and the overall sustainability of food production systems (Day et al., 2005; Glaser, 2007; Laird, 2008; Lehmann et al., 2006; Marris, 2006). is approach to sustainable soil management is modeled on the C-rich anthropogenic soils known as “Terra Preta do Indio” (Indian Black Earth) found in Amazonia and associated with habitation sites of pre-contact Amerindian populations dating as far back as 7000 yr BCE (Glaser, 2007; Glaser et al., 2001; Mann, 2002). e defining characteristic of Terra Preta soils is the presence of large quantities of charcoal in the soil organic matter (Sombroek et al., 1993) to depths of 1 m or greater (Glaser et al., 2000; Lima et al., 2002; Sombroek et al., 1993; Woods and McCann, 1999). ese soils have remained fertile and en- riched in soil C compared with adjacent forest soils despite centuries of cultivation (German, 2003; Woods and McCann, 1999). Recent efforts to replicate the Terra Preta phenomenon show that charcoal addi- tions can have a beneficial effect on highly weathered, infertile tropical soils by increas- Jonathan L. Deenik* Tai McClellan Goro Uehara Dep. of Tropical Plant and Soil Sciences Univ. of Hawaii Honolulu, HI 96822 Michael J. Antal, Jr. Hawaii Natural Energy Institute Univ. of Hawaii Honolulu, HI 96822 Sonia Campbell College of Tropical Agriculture and Human Nutrition Univ. of Hawaii Honolulu, HI 96822 A series of short-term greenhouse experiments and laboratory incubations were conducted to evaluate the effect of macadamia (Macadamia integrifolia Maiden & Betche) nut shell (MNS) charcoal with varying volatile matter (VM) content on soil properties and plant growth in two tropical soils. Lettuce (Lactuca sativa L.) and corn (Zea mays L.) were planted in an Andisol amended with four rates of MNS charcoal (0, 5, 10, and 20% w/w) containing relatively high VM content (225 g kg −1 ) with and without N fertilizer. Increasing rates of charcoal without N caused a significant decline in both lettuce and corn growth. Corn growth declined significantly with or without N at the two highest charcoal rates. In a third experiment, corn growth also declined significantly in an Ultisol amended with the MNS charcoal (5% w/w) with and without fertilizers. In a fourth experiment, charcoals with high VM (225 g kg −1 ) showed negative effects on plant growth while the low-VM (63.0 g kg −1 ) charcoal supplemented with fertilizer showed a significant positive effect on corn growth. Results from the 2-wk incubation experiments showed that high- VM charcoal caused a significant decline in soil NH 4 + –N and a significant increase in soil respiration compared with the soil amended with low-VM charcoal and the soil alone. We propose that phenolic compounds and other products in the high-VM charcoal stimulated microbial growth and immobilization of plant-available N. Our results demonstrate that VM content appears to be an important property of charcoal that has short-term effects on soil N transformations and plant growth. Longer incubation experiments and field trials are needed to further elucidate the role of charcoal VM content on soil processes and plant growth. Abbreviations: DM, dry matter; FC, flash carbonization; GC-MS, gas chromatography–mass spectrometry; MNS, macadamia nut shell; TN, total nitrogen; TOC, total organic carbon; VM, volatile matter.