Soil carbon and nitrogen dynamics by land use and management changes in East and Southeast Asian countries (soil C and N by LUMC)

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 the most 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 paddy-upland 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.

Figure 1. A photograph of the symposium participants.

Figure 2. Partial participants visited the LUMC site near Kumagai Shrine, Shonai Town, where was known as birthpace of famous rice cultivar Kamenoo.

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 and management 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) describe the effects of the long-term application of organic matter on soil C accumulation and GHG emissions from a rice paddy field in a cool-temperate region, Japan. They compare the differences between rice straw and rice straw compost applications in Niigata Prefecture (Takakai et al. 2020a) and between rice straw compost or livestock manure compost applications over more than 40 years in Akita Prefecture (Takakai et al. 2020b). Nguyen et al. (2020 a, b) describe the effects of long-term applications of conventional rice straw and cow dung compost on the fertility of soil used for rice production Nguyen et al. (2020a) and the N balance (Nguyen et al. 2020b) in paddy fields in Yamagata Prefecture. Nguyen-Sy et al. (2020) report a long-term rice experiment in Yamagata that looked at stable C isotope ratios of water-extractable organic C affected by application of rice straw and rice straw compost. Aside from the effects of long-term applications of rice straw and compost on C and N dynamics in cool-temperate regions in Tohoku and Hokuriku, Toriyama, Amino, and Kobayashi (2020) report how incorporating fallow weed contributes to the N-supplying capacity of paddy soil under organic farming in Tochigi Prefecture, Kanto region. From the same Andosols’ field site, Kautsar et al. (2020) report that stocks of C and N and their potential for mineralization are higher under organic than conventional farming practices. Kimani et al. (2020) describe a pots’ experiment, conducted in Tsuruoka, Yamagata, Japan, in which they studied the effect of incorporating Azolla and dual cropping on CH₄ and N₂O emissions from flooded paddy ecosystems.

The special issue contains two original articles from China: Wu et al. (2020) examined how dissolved organic matter and inorganic N jointly regulate fluxes of GHGs from forest soils with different moisture contents during a freeze-thaw period, and Wu (2020) investigated change in soil microbial biomass and regulating factors in an alpine meadow site on the Qinghai–Tibetan Plateau. In an original article from Korea, Park et al. (2020) report that vegetated ridges and sandbags may not reduce soil erosion and loss of C and nutrients from upland fields. In an original article from Indonesia, Kusumawati et al. (2020) describe the effect of sugarcane monoculture practice on the composition of organic C fractions in soils of different textures. Wong et al. (2020), in their original article from Malaysia, report on how agricultural land affects the physicochemical properties of soils derived from sedimentary rocks in Malaysia. Livestock production plays a leading role in agricultural LUC. Producing biogas from livestock waste and then using the biogas effluent to fertilize crops is a promising option for solving environmental problems caused by expansion of livestock production. Thus, the special issue contains a case study in Vietnam conducted by Minamikawa et al. (2020) on variable-timing, fixed-rate application of cattle biogas effluent to rice using a leaf color chart. As application of biochar to soils is considered to have many benefits for sustainable environmentally friendly agriculture, the issue also contains a case study from Thailand by Sriphirom et al. (2020) evaluating biochar application combined with alternate wetting and drying water management in a rice field as an option for farmers to adopt to mitigate CH₄ emissions. Finally, this special issue on Soil C and N by LUMC includes a case study from Uganda, Africa conducted by Inubushi et al. (2020) on the effect of long-term fertilizer management in NERICA cultivated uplands on the biochemical properties of soil.

I hope that this special issue represents a useful contribution for all who are dealing with C and N dynamics with LUMC in different ecosystems, regions, and countries, particularly in East and Southeast Asian countries. My special thanks go to the SSPN editors-in-chief, the official editor, and our guest editors for managing the editorial process. The authors would like to thank all the reviewers for their time and their valuable comments that improved the quality of the published papers.

Disclosure statement

No potential conflict of interest was reported by the author.