Scaling Up Biochar Use as a Climate Mitigation Strategy

Nepal is one of the poorest countries in Asia with gross domestic product (GDP) per capita at purchasing power parity of $4,008 (World Development Indicators Database 2020) and with over 17.4% of the population living in poverty, mostly in rural areas (Nepal Multidimensional Poverty Index 2021).

Agriculture contributes 23% of the GDP, and two-thirds of the population is engaged in agricultural production (World Development Indicators Database 2020), typically low-tech subsistence agriculture. Rice, maize, wheat, potatoes, sugarcane, and lentils are the main crops grown. Most farms follow a mixed crop-livestock system with the average farm household owning at least two cows.

Agricultural productivity remains one of the lowest in Asia with yields far below the world average. Constraints include a difficult terrain that is vulnerable to climate change and natural hazards, such as droughts, floods, and landslides; poor physical infrastructure; limited access to inputs, markets, and financial services; a low technology base with weak extension services; lack of land tenure security; and decreasing soil fertility.

According to a report from ADB and the World Bank, the frequency of precipitation extremes is increasing in Nepal, where warming is projected to be higher than the global average. Poor communities in remote areas that are living on subsistence agriculture are among the most climate vulnerable.

The current imbalance in the world’s carbon and nitrogen cycle is not just the main cause of climate change, but it is also a direct threat to ecosystems through eutrophication (through nutrient runoff), desertification (through declining soil health), and a decline in biodiversity. Rebalancing through regular recycling of organic material with its high carbon, nitrogen, and phosphorus content is needed.

Biochar has the potential to play a key role in climate mitigation. It not only converts the carbon found in a wide range of biomasses into a stable form but also binds volatile nutrients from biomass residues, thereby recycling them for agricultural use.

Biochar helps improve the soil quality over a long period of time. By itself, it contains insignificant quantities of plant nutrients, such as nitrogen, phosphorus, and potassium (NPK), and less than 1% of agricultural lime (calcium carbonate) although nutrient content may vary according to the type of feedstock used. The main contribution of biochar to the project is to enhance the efficiency of nutrient uptake by plants and improve soil quality.

In response to requests from farmers and local service providers for a knowledge solution that addresses in particular drought-prone areas with poor soil fertility and poor access to fertilizers, ADB initiated in October 2011 discussions with the Government of Nepal regarding the potential utilization of biochar as part of an ecosystems approach for rural sustainable growth of farmers and ancillary industries, which led to the development of a 2-year project. The project’s focus was to test and introduce biochar as a strategy for addressing climate change mitigation and for improving soil health, fertility, and plant productivity while reducing energy-intensive agriculture inputs. This aligns with the government’s Agriculture Development Strategy, which promotes the use of organic fertilizers and biofertilizers to help sustain soil fertility and seeks to reduce dependence on fertilizer imports and increase self-sufficiency of farmers, especially those in remote areas.

Biochar can be produced at an industrial scale with automated, highly controlled, and expensive machines or at a much lower investment using manual labor at a farm. Photo credit: Landell Mills.

Depending on the feedstock and process parameters, biochar has a surface area of up to 400 square meters (m2) per gram and can hold up to six times its own weight in water (Schmidt et al. 2015). When mixed with liquid organic nutrients (e.g., animal manure or urine), the inner surfaces of this porous material get coated with complex organic nutrients (Schmidt et al. 2015). Biochar may thus soak up nutrients and increase the efficiency of fertilizer utilization by reducing fertilizer leaching to the subsoil, becoming an efficient organic fertilizer.

Biochar can be produced using different equipment at different levels of production—from industrial scale production with automated, highly controlled, and expensive machines costing more than $500,000 to farm-scale production, which needs much lower investments but requires manual work.

The project found that the most appropriate technology for biochar production at the farm level in Nepal is the soil-pit Kon-Tiki flame curtain kiln. Benefits include high-quality biochar production, low emissions, no need for start-up fuel, fast pyrolysis time and, importantly, easy and cheap construction and operation, with no initial capital investment except labor. The technology is thus affordable to small-scale farmers.

Using the Kon-Tiki flame curtain pyrolysis equipment, a farmer can produce 500 liters of high-quality biochar in about 2 hours from his farm’s biomass leftovers (i.e., corn stover, rice straw, feed leftovers). During the biochar production, a considerable amount of heat is produced, which can be used for various purposes, such as crop drying, pasteurization, hot water production, or essential oil production.

The project identified Eupatorium spp. as one of the most effective feedstocks for preparing biochar in the country. Locally called banmara, meaning “forest killer,” this invasive plant species is commonly found in forest provinces, farm uplands/lowlands, and riverbanks. Eupatorium is naturally regenerated; hence, biochar can be sustainably produced every year. However, depending on the feedstock availability in different regions of Nepal, other available feedstock—especially animal feed leftovers and crop wastes— are equally suitable for biochar production.

To maximize crop yields, the biochar is first enriched with animal urine (e.g., from cattle). For example, the biochar may be soaked in animal manure (urine recovery) pits and mixed with compost. When applying the biochar to crops, the most effective method is root zone application.

Urine was found to be more effective than mineral NPK in enriching biochar. The resulting biochar–urine blend becomes a broadband fertilizer containing 10 kilograms (kg) of nitrogen and 10 kg of potassium per cubic meter (m3). A farmer who owns two cows can produce 7 to 10 m3 of organic biochar fertilizer per year. This amount of organic fertilizer contains 120 kg of nitrogen worth more than 10,000 Nepalese rupees ($84), which is enough to fertilize half a hectare (ha), the average size of a Nepali farm, for a year.

Overall, the average Nepali farmer could annually sequester the equivalent of at least three tons of carbon dioxide equivalent (tCO₂e) by using this biochar system.

Higher yields were observed in field trials for all crops tested—including a 20% increase for tomatoes, 70% for tea, 200% for cabbage and chili, and 300% for pumpkin.

While yield increases were observed to be higher in degraded soils, they were also experienced in fertile soils and across the three main agroclimatic zones.

While biochar-based fertilizers cost in terms of the NPK value, labor requirements to fetch fuelwood, etc., the cost is lower than importing chemical fertilizers.

Farmers saw higher gross margins, which translate into increased farm income. Incremental profit increases ranged from NRs43,000 per ha for potato to NRs550,000 per ha for cabbage.

Biochar-based fertilizers offer a route to promote the scale-up of the production of organic crops, which can attract price premiums as well as bring health benefits but was constrained by low yields. With government support, biochar development has made the improvement of soil health and the development of organic farming a priority.

While biochar utilization presents a good opportunity to increase farm incomes in Nepal and elsewhere in the developing world in a climate-friendly manner, the project showed that several constraints need to be overcome to facilitate widespread use.

Short labor supply in rural Nepal. Given the labor requirements of supporting even the modest application rate of less than 2 tons per hectare, farmers will likely be applying biochar selectively on high value crops only, such as vegetables, even though yield increases are observed for staples such as rice.

Competing uses for charcoal (for cooking, brick production, iron melting, and electricity). Such uses present a low risk against utilizing it for crop production, which is a new and thus potentially risky technique for farmers.

Lack of feedstock for biochar. In places where shrubs, such as Eupatorium, are not available, crop residues may be the only option, but these are also used as animal feed.

Inadequate support services. The government extension system in Nepal lacks the capacity to promote the scale-up of biochar use. A certification system for organic farming is needed to allow farmers to benefit from price premiums.

Lack of a low-cost system for obtaining carbon credits. The main value of biochar is the substantial yield increase that can be obtained with organic enhanced biochar. As the applied biochar amounts are low, the potential carbon credits may be too low to consider establishing a carbon credit payment system for the respective farmers, given the transaction costs.

Additional research is needed on the use of biochar as an animal feed additive. Biochar as an addition to animal feed or as a component of animal bedding and liquid manure recovery provide important economic, ecologic, and health benefits to the animals (e.g., better digestion, less hoof problems), to the farmers taking care of the animals (e.g., less infections, less toxic emissions), and to the environment (e.g., less nitrate and phosphate leaching, less water contamination, less greenhouse gas emissions).

If farm incomes increase because of biochar utilization, then a number of these constraints will disappear. For example, there may be less need for family members to travel to cities for work, and farmers will value biochar and feedstock over other competing uses.

To encourage scale-up, the government, with donor support if required, should provide support to leverage the extension system in promoting biochar production and application (which can then leverage farmer-to-farmer learning, which occurred “organically” in project villages) and in developing certification systems for organic farming.

Asian Development Bank and Nordic Development Fund. 2017. Biochar Development in Nepal: Implementation and Lessons. Unpublished.

Asian Development Bank (ADB). 2016. Mainstreaming Climate Change Risk Management in Development - Sustainable Rural Ecology for Green Growth: Final Report. Manila.

ADB. Nepal: Mainstreaming Climate Change Risk Management in Development.