LAUSR

Atmospheric concentrations of greenhouse gases (GHGs) have increased since the Industrial Revolution. Over the last 260 years, the concentration of atmospheric carbon dioxide (CO2) has increased primarily as a result of fossil fuel emissions, but artificial deforestation and other land-use change is estimated to contribute half of fossil fuel emissions (IPCC 2013). Soils could be carbon (C) sinks or sources depending on land use and management changes (LUMC) in different plant-soil ecosystems. Soil nitrogen (N) and its dynamics not only affect plant growth and crop production but also control sequestration of soil C. Thus, C and N dynamics affected by LUMC in terrestrial ecosystems contribute not only to global and local environmental problems, including global warming, destruction of the ozone layer, acid rain, and eutrophication but also to changes in soil fertility and crop production related to human sustainable development. The global human population is higher than 7 billion, 60% of which are in Asia. East and Southeast Asia have become themost active region in the world. Studies of C and N dynamics by LUMC in East and Southeast Asian countries should be of considerable importance in resolving not only environmental problems but also human sustainable development. There are many types of LUMC in East and Southeast Asian countries. For example, in Indonesia, there is rapid destruction of natural tropical forests for agricultural lands and rice paddies are used as uplands or paddyupland rotation and partly abandoned to natural lands in Japan. However, the numerous findings from LUMC studies on soil C and N dynamics with GHGs in East and Southeast Asian countries have not been disseminated sufficiently and have not been adopted in resolving environmental problems and human sustainable development. Therefore, we held the ‘International Symposium on C and N Dynamics by Land Use and Management Changes in East and Southeast Asian Countries’ on September 10–12, 2018 in Tsuruoka campus, Yamagata University, Japan. The symposium was attended by approximately 70 participants from 10 countries, including 18 Japanese, 17 Chinese, 15 Indonesian, 7 Vietnamese, and 4 Korean (Figure 1). During a one-and-a-half day presentation program, 19 oral and 30 poster presentations including 6 invited keynote lectures were made. During the remaining time, most participants visited the LUMC fields in Shonai Area, Yamagata, where they could see land-use change from sand dune to black pine forest and vinyl rice paddy, LUMC from rice paddies to uplands, orchard, parking area and abandonment to wetland (Figure 2), and large-scale land-use change from original forests to pasture lands. As much of the research presented in the symposium is valuable, original, and has not been published yet, we organized a special issue ‘Soil carbon and nitrogen dynamics by land use andmanagement changes in East and Southeast Asian countries (Soil C and N by LUMC)’ in Soil Science and Plant Nutrition (SSPN). In addition, we also collected original related papers from colleagues from East and Southeast Asian countries who did not attend the symposium. Finally, we accepted 20 papers, including 4 review papers and 16 original articles, for publishing in this special issue of Soil C and N by LUMC. Rice is one of the world’s most important crops, and it is the most important food crop in East and Southeast Asian countries. Rice cultivation is the major emitters of GHGs, particularly methane (CH4). As approximately 90% of rice is produced and consumed in Asia, Asian scientists must take on the task of reducing emissions of GHGs from rice production to mitigate global warming. In respect of mitigating GHG emissions from rice cultivation in Southeast Asian countries, Yagi et al. (2020) reviewed the potential and promisingness of technical options for water management, application of biochar, organic matter management, fertilizer and other amendments, planting methods, and selection of cultivars. This review referenced many papers published in a former special section as ‘Frontline research in mitigating greenhouse gas emissions from paddy fields’ in SSPN (Yagi 2018). This special issue contains four original articles concerning GHG emissions from rice paddies (Kimani et al. 2020; Sriphirom et al. 2020; Takakai et al. 2020a, 2020b). Southeast Asian countries have wet and dry seasons resulting from a seasonal shift in winds or monsoons. During the monsoon season, the tropical rain belt produces additional rainfall. Given this particular climate, the C and N dynamics in the region differ from those in the temperate climate areas studied by many European and North American scientists. In this issue, Purwanto and Alam (2020) review how intensive agricultural management affects the C and N dynamics in the humid tropics. Many East and Southeast Asian countries have long coastal areas, parts of which are used for rice production. Lim et al.’s (2020) review of LUMC for sustainable rice production and C sequestration in reclaimed coastal tideland soils in South Korea should be a valuable reference for other Asian countries. In East Asian countries with temperate and cool-temperate zones, the typical LUMC is changed from grassland to cropland. To clarify whether tillage and conversion of grassland to cropland always depletes soil organic C, Mukumbuta and Hatano (2020) review their group studies in Shinhidaka city, Hokkaido, Japan for this special issue. The special issue contains 16 original articles on LUMC in 7 East and Southeast Asian countries and in 1 African country; this was conducted by Japanese researchers. Eight of the original articles are from Japan. Takakai et al. (2020a, 2020b) SOIL SCIENCE AND PLANT NUTRITION 2020, VOL. 66, NO. 1, 34–36 https://doi.org/10.1080/00380768.2020.1718923