Original article Biochar and rice straw have different effects on soil productivity, greenhouse gas emission and carbon sequestration in Northeast Thailand paddy soil Nipa Thammasom, a Patma Vityakon, a Phrueksa Lawongsa, a, b Patcharee Saenjan a, * a Department of Land Resources and Environment, Faculty of Agriculture, Khon Kaen University, Khon Kaen 40002, Thailand b Agricultural Biotechnology Research Center for Sustainable Economy: (ABRCSE), Khon Kaen University, Khon Kaen 40002, Thailand article info Article history: Received 21 April 2015 Accepted 2 January 2016 Available online 25 June 2016 Keywords: C gas loss Eucalyptus Organic material decomposition Soil fertility abstract This study aimed to clarify the effects of biochar (BC made from Eucalyptus camaldulensis Dehnh.), and rice (Orysa sativa L.) straw (RS) amendments on the soil productivity, carbon sequestration (Cseq) and the possibility for mitigating greenhouse gas (GHG) emissions. A field trial was conducted with 10 treat- ments: the control, chemical fertilizer (CF) and BC or RS each at four rates of L (6.25 t/ha), ML (12.50 t/ha), MH (18.75 t/ha) and H (25.00 t/ha) using a randomized complete block design with four replicates. The results showed that BC and RS not only increased the soil quality but also increased the rice yield (RY). During the growing season, BC and RS applications did not differ in the total CO 2 emission. However, the total CH 4 emission and total global warming potential significantly decreased in the BC application and significantly increased in the RS application, relative to the control. Soil Cseq increased under the BC application by 1.87e13.37 t C/ha, while the RS application reduced Cseq by 0.92e2.56 t C/ha. The high amount of recalcitrant C molecules in BC probably explained the decreases in the GHG-C loss and in- creases in Cseq. In contrast, RS had high amounts of labile components that enhanced the GHG-C emission and reduced Cseq. Finally, the GHG intensity of rice production was reduced for both BC and RS meaning that these two amendments can be considered as good options for the mitigation of climate change. Copyright © 2016, Kasetsart University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Introduction Long term, poorly managed rice culture in Northeast Thailand has decreased the soil organic carbon (SOC) content resulting in degraded paddy soils with low productivity; to counteract this, leftover rice stubble and straw (RS) is usually incorporated into the soil to improve the fertility and rice yield (RY) and to maintain the SOC (Xiao et al., 2007; Hanafi et al., 2012). RS application increases the SOC as a function of application amounts and duration. For instance, RS added into paddy soils increased seasonal soil carbon sequestration (Cseq) by 0.10 t C/ha and 0.36 t C/ha at an application rate of 2.625 t/ha and 4.5 t/ha, respectively, in a long term field experiment (Xionghui et al., 2012). However, RS is an easily decomposable organic material that provides major substrates for methanogens that contribute to methane (CH 4 ) and carbon dioxide (CO 2 ) production resulting in increases in the global warming po- tential (GWP; Le Mer and Roger, 2001). Biochar (BC) is a stable, C-rich form of charcoal which can be applied to crop lands as an amendment to improve the soil pro- ductivity, reduce greenhouse (carbon) gases (GHG) and enhance soil Cseq (Lehmann, 2007). Assessment of the BC effects in a field trial in China revealed that BC application at rates of 10 t/ha and 40 t/ha improved the rice yield (RY) by 12 percent and 14percent, respectively (Zhang et al., 2012a). Moreover, the initial C loss as CO 2 emission was negligible compared to the amount of intrinsic C stored within the BC itself (Jones et al., 2011). Indeed, BC can remain in soil for hundreds to thousands of years (Sohi et al., 2009; Sparkes and Stoutjesdijk, 2011), providing an alternative for sequestering C in soil (Lehmann et al., 2006; Shen et al., 2014). Accordingly, the possibility to use BC derived from eucalypt trees that grow abun- dantly in Northeast Thailand should be examined as a potential soil amendment for reducing GHG emissions in paddy soils. The contrasting chemical characteristics between BC (from eu- calypts) and RS may lead to different decomposition rates when * Corresponding author. E-mail address: patsae1@kku.ac.th (P. Saenjan). Contents lists available at ScienceDirect Agriculture and Natural Resources journal homepage: http://www.journals.elsevier.com/agriculture-and- natural-resources/ http://dx.doi.org/10.1016/j.anres.2016.01.003 2452-316X/Copyright © 2016, Kasetsart University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). Agriculture and Natural Resources 50 (2016) 192e198