- A new study shows that Bhutan has the potential to sequester 68% of its greenhouse gas emissions through biochar, a carbon-rich material made from organic waste that is used to help plants grow.
- The research shows that using crop residue as mulch and biochar can significantly increase yields; however, many farmers in Bhutan do not know about biochar nor do they have access to the raw materials, such as rice husks, necessary for its production.
- While many studies note biochar’s potential for mitigating climate change, some research shows that too much biochar under certain conditions can harm soil, soil organisms and water availability and can cause soil erosion.
A recent study reveals Bhutan’s potential to store 68% of its greenhouse gas emissions by converting crop residues into biochar, the highest among 12 countries noted in the report. This innovative approach could position Bhutan as a leader in sustainable agriculture and significant emissions reduction.
Biochar is a carbon-rich, lightweight, black material that looks like charcoal and is used in soil to help crops grow. It has potential for mitigating climate change because the carbon in biochar can remain in the soil for a long time, rather than being released into the atmosphere as CO2.
Globally, biochar has gained popularity due to its potential for mitigating climate change and improving soil health. A 2021 research review shows that biochar can store carbon, reduce greenhouse gases, boost plant growth, clean up heavy metal pollution and improve resource use, making it important for climate action, food security and sustainable practices.
But the full potential of crop residue for use in biochar had not been fully studied, so a research team set out to create a set of high-resolution maps indicating crop residues and their estimated potential use in biochar in countries around the world. Bhutan came out on top.
By turning crop leftovers into biochar, Bhutan can lower its emissions even more. Bhutan is already considered carbon-neutral, with emissions of 1.559 megatons of CO2, not counting land use changes and forestry. The country’s constitution requires 60% of land to be under forest cover at all times, which aids Bhutan’s position as a carbon sink. However emissions in the transport and industry sectors have been increasing in recent years, according to IMPACT, an economic model created in the early 1990s to help policymakers tackle hunger and poverty in a sustainable way.
But biochar is still new to most Bhutanese farmers, local experts say, and it’s currently difficult for growers in some regions to get their hands on the necessary raw materials.
Stephen Wood, a senior scientist in agriculture and food at The Nature Conservancy and co-author of the study, told Mongabay in an interview that the group’s research in India and Bhutan revealed that using crop residue as mulch and biochar significantly improved soil health and crop yields by 36%-64%. The study involved more than 1,400 local farmers in India and more than 100 in Bhutan adopting these practices. The findings also show that turning all global crop leftovers into biochar could store up to 1 billion metric tons of carbon each year. After 100 years, three-quarters of this carbon would still be stored, potentially offsetting about 80% of greenhouse gas emissions from agriculture.
“They provide guidelines for environmentally friendly crop residue management to boost agricultural yield and soil quality,” Wood said.
Bhutan has currently adopted rice husk biochar and wood chip biochar on a small scale, with biochar identified as a fertilizer and soil conditioner of plant or animal origin that is listed in the government’s standard for organic products. Biochar produced from rice husks in a modified kiln is used as a potting mix component, soil amendment, hydroponics substrate and mulch in the west-central districts of Bhutan. The country’s Agriculture Research and Development Centres (ARDC) use the technology for plant nurseries and research.
Wood noted that the nursery plants on which biochar is used are comparatively healthier. Farmers also reported decreased incidences of soil-borne diseases and increased yields in crops such as chiles, cole crops (in the cabbage family) and maize in the two districts of western Bhutan.
Yeshey Zangpo, senior agriculture supervisor with the Ministry of Agriculture and Livestock, mentioned that not all crop residues can be used for biochar. But rice husk, abundant in the country, is cost-effective and doesn’t turn into ash under heat due to its silicon content. Ash is what’s left after burning biomass in the open, and it contains minerals such as potassium that aren’t good for plant growth. Biochar, on the other hand, is a charcoal-like substance made by burning biomass without oxygen. This process also produces bio-oils and syngas, which can be used to generate heat or electricity. The leftover biochar can be added to soil to improve its quality by storing carbon, retaining water and nutrients and even helping to control harmful soil organisms. Many researchers worldwide are studying the benefits and drawbacks of using biochar. Once produced, biochar can be spread on top of the soil, buried or mixed with compost or seeds.
Yeshey explained that rice husk biochar, as a soil amendment innovation, helps sequester carbon by converting the carbon content in the raw materials (husk) and feedstock (straw) to char, which conserves soil moisture and nutrients.
Although Bhutan is carbon negative, maintaining carbon in the soil would further enhance carbon stock by preventing its release, contributing to global carbon stock. Mitigating climate change through biochar could be a future priority, as it is considered a “climate-smart agriculture” technology.
A study by Birkha Bahadur Tamang, an agricultural researcher with the ARDC, published in the Bhutanese Journal of Agriculture examined wood-derived biochar as a growing medium for kiwifruit seedlings in Bhutan. The findings showed that kiwifruit seedlings had significant positive growth responses to biochar-amended media, with the best results using a mixture of 25% biochar and 75% compost.
Similarly, a study published in the Asian Journal of Agricultural Extension Economics & Sociology investigated the effects of biochar on soil properties and the growth and yield of chile in Samtenling, Bhutan’s wet subtropical agro-climatic zone. It found that biochar greatly improved chile yields, pod weight per plant and number of pods per plant, with the best results at 3.2 tons per acre. Higher amounts of biochar reduced yields, showing there’s a limit to its effectiveness.
Smallholder benefits
Wood said that globally, the technology benefits smallholder and commercial farmers, offering enterprise opportunities to women in floriculture, horticulture and nursery businesses.
However, the innovation is yet to be widely adopted on a commercial scale in Bhutan. Yeshey noted that farmers are adopting biochar on a small scale as it is still new, and raw materials are not readily available in non-rice-growing areas.
Known as the country’s “vegetable capital,” Tsirang is one of the highest producers in the country. There, in the southern part of the country, Tek Bahadur Sunwar started a farmers group in 2020 that focuses on commercial ginger production. Sunwar said that the district agriculture sector trained farmers in biochar processing and production, but through his experience, biochar application is not effective for rhizomes like ginger. The 19-member farmer group mostly uses organic manure and cow urine to tackle outbreaks of pests and diseases on their 12-hectare (30-acre) commercial farm.
Not everyone in eastern Bhutan knows about the technique either. Rinzin Lhamo and her five friends in eastern Bhutan have never heard about the biochar method. The six-member female group grows vegetables and other agricultural products. While they had heard about soil-enhancing substances such as urea, their focus is on organic production, Lhamo said.
Another farmer’s group in Mongar district in the east did not hear about biochar use in the fields either. They use organic manure to grow commercial vegetables that are supplied to schools in the district. Moreover, the founder of the commercial farmer’s group, Sonam Jamtsho, said that as they do not grow paddy, the raw materials are not easily available to them for biochar production.
Meanwhile, a farmer’s group in central Bhutan said they did not get any kind of support or training from the Ministry of Agriculture and Livestock on soil enhancement methods. “We simply use organic manure,” the chairman, Phub Dorji, said. They feed the paddy straw to livestock. “If there is such skill development training, we are keen to learn,” Dorji added.
Studies say that research centers promote soil amendment technologies as climate-smart solutions, but farmers are hesitant to adopt them because they don’t see immediate, noticeable benefits that justify the resources required. To encourage adoption, clear evidence of the technology’s value is needed, and policies should guide institutions with this evidence.
The lack of dissemination of scientific studies, Yeshey said, poses challenges, as people are reluctant to adopt the method. He cited the example of researchers not being able to quantify the amount of soil carbon fixed and carbon from raw materials reduced to char.
If biochar is to grow into a large industry, new innovations are needed to make it cheaper and more efficient, and farmers need to be informed of its benefits to use it effectively.
Wood said incentives are key to achieve that. Farmers need to be able to affordably procure and easily apply biochar to their fields, and there must be returns on their investment, either in improved crop yields or payments for ecosystem services.
Yeshey said providing awareness programs on use and benefits through hands-on training would scale up adoption of biochar within Bhutan. Apart from a few video materials on biochar produced by the Ministry of Agriculture in Dzongkha, the national language of Bhutan, the innovation is not widely promoted to farmers.
Despite its benefits, biochar use is not without controversy. A review of 259 studies published in 2021 raised concerns about the long-term safety of using biochar. The researchers found that too much biochar under certain conditions can harm soil, soil organisms and water availability and can cause soil erosion. High doses can degrade soil by changing its pH and nutrient balance, making it less fertile. While biochar can help retain water and nutrients, if not managed well, it can reduce water absorption and increase runoff.
Banner image: A farmer applies biochar in the field. Image courtesy of the Ministry of Agriculture and Livestock, Royal Government of Bhutan.
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Citations:
Karan, S. K., Woolf, D., Azzi, E. S., Sundberg, C., & Wood, S. A. (2023). Potential for biochar carbon sequestration from crop residues: A global spatially explicit assessment. GCB Bioenergy, 15(12), 1424-1436. doi:10.1111/gcbb.13102
Kabir, E., Kim, K., & Kwon, E. E. (2023). Biochar as a tool for the improvement of soil and environment. Frontiers in Environmental Science, 11. doi:10.3389/fenvs.2023.1324533
Tamang, B. B., Dorji, T., & Dorji, L. (2021). Effect of wood-derived Biochar as growth and development medium for Kiwifruit seedlings. Bhutanese Journal of Agriculture, 4(1), 28-37. doi:10.55925/btagr.21.4103
Wangmo, T., Dorji, S., Tobgay, T., & Pelden, T. (2022). Effects of Biochar on yield of chilli, and soil chemical properties. Asian Journal of Agricultural Extension, Economics & Sociology, 64-77. doi:10.9734/ajaees/2022/v40i930976
Brtnicky, M., Datta, R., Holatko, J., Bielska, L., Gusiatin, Z. M., Kucerik, J., … Pecina, V. (2021). A critical review of the possible adverse effects of biochar in the soil environment. Science of The Total Environment, 796, 148756. doi:10.1016/j.scitotenv.2021.148756
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