Biochar, generally recognized as carbonated biomass generated by partial pyrolysis under a limited supply of oxygen gas, has attracted attention worldwide for its prospective functions to improve agricultural productivity, sequestrate carbons, etc. It seems to become quite popular after the finding of the benefits of terra preta, known as ‘Amazonian dark earth’ or ‘Indian black earth,’ which contains a large amount of weathered charred materials together with other wastes originating from human activity. Because terra preta is more fertile and richer in carbon content than the adjacent soils, we are expecting the beneficial functions of biochar in soils.
Research on biochar has been reported and reviewed in many scientific journals for decades. Soil Science and Plant Nutrition (SSPN) has also published such reports on biochar. However, we would like to encourage researchers to share more information on this topic in this journal, because SSPN is a leading journal, especially in East and Southeast Asia, and the regions have a long history of biochar utilization. Especially in Japan, the annual burning of seminatural grasslands in early spring is a traditional practice to keep grassland vegetation against succession to shrubs and forests, and this activity would generate charred materials there. Burning of rice fields after harvesting had been also a common agricultural practice before the burning had been banned by the Japanese government, and rice-growing farmers are good at preparing rice husk biochar. In addition, in 2020, the Japanese government has approved the biochar application in soils as an effective way of carbon sequestration in the J-Credit Scheme, which aims to certify the amount of greenhouse gas removal from the atmosphere and facilitate greenhouse gas emission trading. Focusing on soils, Japanese Andosols are special, because they are able to accumulate an extremely large amount of carbon, such as 10 to 20%, in their thick humus horizons. Many soil scientists have pointed out that at least a part of the carbon accumulated in Andosols is originated from charred materials. All such information would deserve sharing for the effective use of biochar in many other countries, and SSPN will be an adequate platform.
In general, the purpose of biochar application in arable soils is to improve productivity in agriculture. In addition, we are expecting the ability of biochar to sequestrate carbon in soils too, because biochar seems much stabler than other biomass. These functions are fascinating because the biochar application can further accelerate carbon removal from the atmosphere by accelerating CO2 fixation by plants and it would be a promising countermeasure against global warming. To utilize biochar effectively, it would be important to understand the underlying mechanism of the phenomena on the basis of scientific evidence. We also need to consider the sustainability of soils not only from agronomical but also ecological perspectives, because biochar would persist and exert its effects on soils for a long time.
To begin with, we here provide a special section entitled ‘past, present, and future biochar utilization for soil sustainability from Asian agronomical and ecological perspectives.’ It means that the special section is not a destination, but just a starting point of biochar research in SSPN. In the special section, several reviews are invited to summarize the past findings on the function and utilization of biochar, and some new findings will appear. We hope that this special section will be an opportunity for more research findings to be published in SSPN in the near future.