Biochar is a solid material derived from the thermochemical conversion of biomass such as wood, grass, and livestock manure under limited oxygen conditions. Biochar has received increasing attention due to its potential to improve the soil environment and mitigate climate change through carbon dioxide removal. When applied to mineral soils, biochar can enhance soil fertility and moderately increase soil pH in acidic soils, offering a promising approach to sustainable agriculture. However, its application requires consideration of the soil pH and adherence to safety regulations.

The beneficial properties of biochar, including its high specific surface area, cation exchange capacity, and nutrient content, depend on the feedstock and pyrolysis methods. Wood-based biochar generally has a higher carbon content, whereas manure-based biochar tends to provide more plant-available nutrients. Its porous structure provides habitats and retains nutrients for soil microorganisms, which play a crucial role in nutrient cycling and the maintenance of soil ecosystems.

To streamline estimating soil carbon sequestration using biochar, a new method using proximate analysis based on the Japanese Industrial Standard (JIS) M 8812 was developed. This method estimates the pyrolysis temperature and carbon sequestration potential by analyzing the volatile matter and fixed carbon content. However, biochar production processes, including feedstock collection, pyrolysis, and transportation, often rely on fossil fuels and electricity. Therefore, assessing the net environmental impact, including associated CO₂ emissions, using life cycle assessment is necessary to ensure the role of biochar in achieving carbon neutrality.

Effective biochar production requires pyrolysis temperatures exceeding 350 ℃ and careful management of gases and smoke emissions. Given the seasonal and dispersed availability of local unused biomass, selecting appropriate pyrolysis systems is essential for maintaining economic feasibility and avoiding overinvestment. In the Asia–Monsoon region, cereal crop residues, particularly rice husk, and straw, are the most abundant feedstocks, followed by perennial crops such as sugarcane. The annual biochar production potential is estimated at 700 million tonnes, accounting for approximately 3.7% of the region’s total greenhouse gas emissions in CO₂ equivalents.

Biochar application rates should account for the diverse soil conditions across Asia. Due to its low nitrogen content compared to phosphorous and potassium, supplementing biochar with nitrogen sources, such as manure or compost, is recommended. Although biochar generally meets the safety thresholds for heavy metals, PAHs, and dioxins, biochar derived from sludge and animal waste may require additional attention because of its potentially higher heavy metal content in some cases. Fresh biochar in soil can reduce the efficacy of herbicides and pesticides. Further research is necessary to understand its long-term interactions with soil and plants in agricultural systems, and especially how biochar properties affect root remediation potential and microbial nutrient cycling.

Robust policy frameworks and incentives are essential to promote the implementation of biochar. These include subsidies for carbon removal and credits related to the amount of carbon removed. Japan has been at the forefront in this area, with its Ministry of Agriculture, Forestry and Fisheries offering subsidies to support biochar production and application. Socio-economic systems that balance short-term economic profitability with long-term sustainability, such as the COOL VEGE® eco-brand initiative launched in 2008 in Kameoka City, Kyoto Prefecture, are effective models for advancing biochar adoption.

By addressing these challenges and integrating biochar into agricultural practices, its potential for enhancing soil environment, contributing to sustainable agriculture, and mitigating climate change can be further realized.