Paddy fields are recognized to be a major anthropogenic source of atmospheric methane (CH4), a potent greenhouse gas with a relatively short lifetime in the atmosphere. Like other biogenic sources, CH4 is produced by the activity of CH4-producing archaea, or methanogens, as one of the terminal products in the anaerobic food web in flooded soils. Due to the large amount of CH4 emitted globally from paddy fields, mitigation of emissions from this source is very important in order to stabilize its atmospheric concentration. In addition, because of the possibility of controlling these emissions by agronomic practices, such as management of water, fertilizer, and organic matter, paddy fields appear to be one of the most promising sources for mitigating CH4 emissions.
The mechanisms and factors controlling CH4 production in flooded soils were systematically elucidated almost 50 years ago, mainly by laboratory experiments. Field measurements of the emissions from paddy fields have been conducted at various locations of the world since the early 1980s. Compilation of these data provided the emission and scaling factors for CH4 from rice cultivation in the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Trade-offs and synergies of mitigating CH4 emissions with N2O emissions or rice production have also been studied. As a result, an array of options that mitigate greenhouse gas emissions from paddy fields has now been proposed and demonstrated by field experiments.
However, there is a strong social need, as the next step of research advancement, to develop implementation strategies for extending the options successfully to local farmers and communities. Because the systems of rice cultivation are widely diverse depending on climate, social, and economic conditions, the options often need to be developed in accordance with those regional conditions. Also, it is necessary to improve the sharing of knowledge of the mitigation options among researchers and other stakeholders, such as policy makers and land users, in different regions of the world. These endeavors are particularly crucial to set up nationally appropriate mitigation actions for rice producing countries, in order to undertake ambitious efforts to combat climate change and meet the 2016 Paris Agreement on Climate Change.
This special section, ‘Frontline research in mitigating greenhouse gas emissions from paddy fields’, has been proposed to address the current research needs. Research papers on the issue were collected through the framework of the Paddy Rice Research Group of the Global Research Alliance on Agricultural Greenhouse Gases (GRA). They were submitted and peer reviewed by entirely the same processes as other papers published in the Soil Science and Plant Nutrition (SSPN). I hope the papers included provide the frontline of research challenge to this globally important issue and contribute to the focus of the GRA that brings countries together to find ways to grow more food without growing greenhouse gas emissions.
Last but not least, I would like to thank all the reviewers for their valuable comments and the SSPN Editorial Board for giving us the opportunity to publish this special section.