TECHNICAL REPORTS 1052 With a growing world population and global warming, we are challenged to increase food production while reducing greenhouse gas (GHG) emissions. We studied the efects of biochar (BC) and hydrochar (HC) produced via pyrolysis or hydrothermal carbonization, respectively, on GHG luxes in three laboratory incubation studies. In the irst experiment, ryegrass was grown in sandy loam mixed with equal amounts of a nitrogen-rich peanut hull BC, compost, BC+compost, double compost, or no addition (control); wetting–drying cycles and N fertilization were applied. Biochar with or without compost signiicantly reduced N 2 O emissions and did not change the CH 4 uptake, whereas ryegrass yield was signiicantly increased. In the second experiment, 0% (control) or 8% (w/w) of BC (peanut hull, maize, wood chip, or charcoal) or 8% HC (beet chips or bark) was mixed into a soil and incubated at 65% water-holding capacity (WHC) for 140 d. Treatments included simulated plowing and N fertilization. All BCs reduced N 2 O emissions by ~60%. Hydrochars reduced N 2 O emissions only initially but signiicantly increased them after N fertilization to 302% (HC-beet) and 155% (HC-bark) of the control emissions, respectively. Large HC-associated CO 2 emissions suggested that microbial activity was stimulated and that HC was less stable than BC. In the third experiment, nutrient-rich peanut hull BC addition and incubation over 1.5 yr at high WHCs did not promote N 2 O emissions. However, N 2 O emissions were signiicantly increased with BC after NH 4 NO 3 addition. In conclusion, BC reduced N 2 O emissions and improved the GHG-to-yield ratio under ield-relevant conditions. However, the risk of increased N 2 O emissions with HC addition must be carefully evaluated. Biochar and Hydrochar Efects on Greenhouse Gas (Carbon Dioxide, Nitrous Oxide, and Methane) Fluxes from Soils Claudia Kammann,* Stefan Ratering, Christian Eckhard, and Christoph Müller T he fertile Terra preta, or Amazonian dark earth (ADE), soils were made by indigenous populations up to 2000 yr ago (Glaser et al., 2001). heir sustained fertil- ity has prompted the idea to add charred materials of biological origin (biochar [BC]) to agricultural soils (Marris, 2006; Steiner et al., 2007; Lehmann, 2007a, b). Pyrogenic black carbon pro- vides the oldest and most degradation-resistant carbon fraction in natural soils (e.g., in chernozem or soils in ire-prone ecosys- tems) (Schmidt et al., 1999; Brodowski et al., 2006; Lehmann et al., 2008; Lehmann et al., 2009; Rodionov et al., 2010). hus, it is at least partially responsible for the large stock of stable carbon in such soils. his ofers an interesting option to use carbon capture (via photosynthesis) and soil storage as a global warming mitigation option as proposed by Ogawa (1991), Seifritz (1993), and Okimori et al. (2003). he idea has gained considerable interest in recent years (e.g., Hansen et al., 2008; Lal, 2009), and its global potential for C sequestration has been assessed by Woolf et al. (2010). However, before applying these additives to soil, which will remain there for centuries to mil- lennia, a careful evaluation of its risks is required (Wardle et al., 2008; Lehmann et al., 2009). For instance, CH 4 oxidation, an important CH 4 –consuming process in aerobic soils (Conrad, 2007), may be inhibited (Priemé and Christensen, 1999), or CH 4 production may be increased (Zhang et al., 2010). It is also possible that BC may cause increased emissions of other greenhouse gases (GHGs), such as CO 2 or N 2 O, under certain conditions (van Zwieten et al., 2009). Methane can be produced under anaerobic conditions by methanogenic Archaea and can be taken up in oxic soils via consumption by methanotrophic bacteria (Conrad, 2007). he impact of BC on CH 4 luxes is unclear due to the lack of data and contrasting results. Biochar reduced net CH 4 uptake (Priemé and Christensen, 1999; Spokas and Reicosky, 2009), had no efect on net CH 4 uptake (van Zwieten et al., 2009), or stimulated CH 4 uptake (Karhu et al., 2011). Reports on CO 2 emissions from BC-amended soils are rather mixed: Some researchers have observed signiicant Abbreviations: ADE, Amazonian dark earth; BC, biochar; GC, gas chromatograph; GHG, greenhouse gas; HC, hydrochar; HTC, hydrothermal carbonization; SOC, soil organic carbon; SOM, soil organic matter; WFPS, water-illed pore spaces; WHC, water-holding capacity. C. Kammann, C. Eckhard, and C. Müller, Dep. of Plant Ecology, Justus-Liebig- Univ. Giessen, Germany, Heinrich-Buf-Ring 26-32, D-35392 Giessen, Germany; C. Kammann and C. Müller, School of Biology and Environmental Science, Univ. College Dublin, Belield, Dublin, Ireland; S. Ratering, Dep. of Applied Microbiology, Justus-Liebig-Univ. Giessen, Heinrich-Buf-Ring 26-32, D-35392 Giessen, Germany. Assigned to Associate Editor James Ippolito. Copyright © 2012 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 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. J. Environ. Qual. 41 doi:10.2134/jeq2011.0132 Received 6 Apr. 2011. *Corresponding author (Claudia.i.Kammann@bot2.bio.uni-giessen.de). © ASA, CSSA, SSSA 5585 Guilford Rd., Madison, WI 53711 USA Journal of Environmental Quality ENVIRONMENTAL BENEFITS OF BIOCHAR SPECIAL SECTION