Effects of crop residue returning on nitrous oxide emissions in agricultural soils Jun Shan, Xiaoyuan Yan * State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China highlights < Effects of crop residue returning on N 2 O release are evaluated by meta-analysis. < Crop residue returning has no obvious effect on N 2 O release compared with controls. < Effects of crop residue on N 2 O emission is significantly affected by land-use types. article info Article history: Received 24 October 2012 Received in revised form 2 February 2013 Accepted 5 February 2013 Keywords: Climate change Nitrous oxide Straw Emission factor Quantitative analysis abstract Crop residue returning is a common practice in agricultural system that consequently influences nitrous oxide (N 2 O) emissions. Much attention has been focused on the effects of crop residue on N 2 O release. However, no systematic result has yet been drawn because environmental factors among different studies vary. A meta-analysis was described to integrate 112 scientific assessments of crop residue returning on N 2 O emissions in this study. Results showed that crop residue returning, when averaged across all studies, had no statistically significant effect on N 2 O release compared with control treatments. However, the range of effects of crop residue returning on N 2 O emission was significantly affected by synthetic nitrogen (N) fertilizer application, type of crop residue, specific manner in which crop residue has returned, and type of land-use. N 2 O release was significantly inhibited by 11.7% and 27.1% (P < 0.05) when crop residue was with synthetic N fertilizer and when type of land-use was paddy, respectively. While N 2 O emissions were significantly enhanced by 42.1% and 23.5% (P < 0.05) when crop residue was applied alone and when type of land-use was upland, respectively. N 2 O emissions were likewise increased when crop residue with lower C/N ratio was used, mulching of crop residue was performed, and type of land-use was fallow. Our study provides the first quantitative analysis of crop residue returning on N 2 O emissions, indicating that crop residue returning has no statistically significant effect on N 2 O release at regional scale, and underlining that the Intergovernmental Panel on Climate Change guidelines should take the opposite effects of crop residue returning on upland and paddy into account when estimating the N 2 O emission factor of crop residue for different land-use types. Given that most of data are dominated by certain types of crop residue and specific application methods, more field data are required to reduce uncertainty. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Concern with the escalating amount of nitrous oxide (N 2 O) emissions is increasing because N 2 O contributes to global warming and stratospheric ozone destruction (Ravishankara et al., 2009; Wuebbles, 2009). Agricultural N 2 O emissions are estimated to ac- count for more than 80% of calculated annual atmospheric N 2 O (Bouwman, 1998). Major anthropogenic N 2 O sources include emissions released directly from agricultural lands and from live- stock production (Kroeze et al., 1999; Mosier et al., 1998; Olivier et al., 1998). N 2 O emissions occur in agricultural soil by chemical denitrification, biological nitrification, and denitrification in which biological processes are dominant (Bouwman, 1998; Duxbury et al., 1982). Moreover, the use of synthetic nitrogen (N) fertilizers, manure, crop residue, and so on, also contributes to the amount of N 2 O emissions (Akiyama et al., 2010; Davidson, 2009). Crop residue from agricultural soil is vital because this resource provides readily available carbon (C) and nitrogen (N), as well as * Corresponding author. Tel.: þ86 (0)25 8688 1530; fax: þ86 (0)25 8688 1000. E-mail addresses: shanjun@issas.ac.cn (J. Shan), yanxy@issas.ac.cn (X. Yan). Contents lists available at SciVerse ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.atmosenv.2013.02.009 Atmospheric Environment 71 (2013) 170e175