Biochar is charcoal made from organic matter such as wood, plant materials, and manure. The organic matter is heated at high temperatures of between 300-900 ℃, with very little oxygen. Biochar is carbon rich, absorbent and does not break down easily like other soil enhancers, therefore it is able to stay in the soil for long periods of time. Thus, it can reduce the need for frequent application of compost while still promoting healthy crop growth. Biochar is a soil amendment that improves soil health by aerating the soil, as well as retaining moisture and nutrients in the soil. Additionally, due to the low oxygen burning method, carbon is locked into the soil instead of being released back into the environment. The materials used for processing biochar can range from small-scale and simple to more complex and commercial.
PRE-CONDITIONS FOR IMPLEMENTATION
Contact local authorities to see if permits are needed to produce or apply biochar.
Conducting a soil test before implementing biochar is recommended to gain a basic understanding of the quality of the soil.
The characteristics of biochar vary slightly depending on the materials used and the burning process followed.
When biochar is added to soil, it sucks up the surrounding nutrients of the soil. Thus, to maximize the benefits, it is important to mix biochar with compost or animal manure at a ratio of 3:1 or 4:1 to enrich it before applying it to the soil. This process is referred to as charging the biochar.
Biochar has a high pH, typically around 8, thus it has the ability to increase the overall pH of the soil. If the soil already has a high pH, incorporating biochar may increase imbalance in the soil.
Be careful when making biochar from invasive species or species that negatively impact the growth of other species, such as black walnut or eucalyptus. Incomplete processing may not completely destroy the harmful chemicals that can inhibit the growth of certain crops.
METHOD OF APPLICATION
Organic Material
A wide range of materials can be used to produce biochar. However, one important thing to consider is that the material should be dry (less than 20% moisture) in order to optimise the burning process by limiting smoke and increasing total yields of biochar. Additionally, the material should be untreated, free from synthetic materials, low in salinity and not contain heavy metals.
Wood based materials such as tree trimming, wood chips, and sawdust
Crop waste such as husks, stalks, dry leaves, weeds, or bamboo
Manure
Production
There are various types of kilns that can be used that range from low-budget to expensive.
Flame cap kiln or flame curtain kilns: Small scale (affordable option)
Retort Kiln: Medium scale
Pyrolysis unit: Commercial/large scale
Flame cap kiln
Flame curtain kiln
Retort kiln
Pyrolysis unit
Accessory equipment (optional)
Shredder or chainsaw if large raw material needs to be broken down
Broadcaster for spreading the biochar quickly on large-scale operations
Compost, manure or compost tea to charge the biochar
Monitoring
Moisture meter
Soil test kit (nutrients, pH, microbial life)
Steps of implementation
Determine type and production of biochar
Conduct a soil test to properly determine the current quality of the soil.
Create the biochar
Ensure the selected material is dry. Shredding large materials may be beneficial for burn quality, but it is not required.
Burn the materials using a controlled, low oxygen kiln of choice. Temperature can vary, but typically ranges between 500-800 ℃. Higher temperatures tend to have a higher pH and more stable carbon.
Cool the biochar by soaking it in water or nutrient dense liquid such as compost tea.
Process the biochar.
Crush the biochar pieces to sizes of about 2mm-10mm, manually or with a shredder.
Charge the biochar with nutrient dense material such as compost tea, compost or manure. Let this sit for up to two weeks before applying it to the land.
Biochar Application
While the application rate of biochar depends on initial conditions and the characteristics of the biochar used, positive effects of application have been seen with rates between 5 to 50 tons per hectare Source.
Mix the biochar into the soil. Ideally biochar is added to the soil surface, in the root zone (5-15cm) where roots can utilise the nutrients in the biochar mixture.
Monitor: About 6-12 months after application, monitor growth and conduct an additional soil test. Keep notes on productivity and growth of crops.
Considerations for application:
Dry, hot biochar can be a fire hazard if exposed to oxygen, thus the best way to handle and store biochar is in an environment that excludes oxygen. This can be done by soaking the biochar in water or compost tea or the biochar can be left to cool completely in a closed space such as a metal container. Here is a guide for handling and processing biochar. Always ensure that you have a secure water source nearby for quenching.
Keep in mind that about 15-22% of the burned material (by volume) will be produced into biochar.
Use dried animal manure sparingly as raw material because it can have high salt/heavy metal content.
Adding moisture to the biochar before application can help with loss due to wind erosion.
Quality of biochar can vary significantly depending on the feedstock used and the production temperature, therefore it is hard to standardize the final product.
BENEFITS
This intervention contributes to:
COSTS
Factor
Estimated Value
Total Cost
Sub-Saharan Africa: Applied at a rate of 12 tons per hectare, the final cost for biochar applied to arable land was $132 USD per ton, with an estimated range of about $99 to $165 USD per ton. Alternatively, application cost ranged from $1187 - $1978 USD per hectare.
North-Western Europe: Applied at a rate of 13 tons per hectare, the final cost for biochar was $207 USD per ton, with an estimated range of about $155 - $259 USD per ton. Alternatively, application cost ranged from $2019 - $3365 USD per hectare Source.
Labour Time
In one study, the labour to produce biochar made up about 27.07% of the overall production and application cost Source.
A separate study estimated that it would take about 4 hours to produce about 1 cubic meter of biochar in a flame cap kiln (excluding the time it took to harvest and prepare the material) Source.
In Stockholm, Sweden, they have developed a method called The Stockholm Tree Pit Method which focuses on the challenge of growing trees in confined spaces within urban areas. They discovered a mix of stones, and a 1:1 ratio of biochar and compost created ideal conditions for the development of trees. Often urban environments face issues including soil compaction and limited space for root growth. The results from the start of the trials of this project indicated that trees planted with biochar had overall better long term growth, including improved root growth, reduced needs for infrastructure maintenance, and more sustainable drainage systems
In this case study, biochar was applied to enhance crop yields and food security by improving soil conditions that support plant growth. Because biochar remains stable in the soil for long periods, it allows for a reduction in nitrogen and phosphorus inputs while maintaining overall productivity. In Benin, farmers produce biochar as a byproduct of daily cooking using small gasifier stoves. These stoves not only reduce the need for firewood but also burn more cleanly, emitting less smoke and carbon into the atmosphere. Common feedstocks include corn husks and tree prunings. Field trials with corn demonstrated an increase in yield from about 0.2 to 0.7 tons per hectare for each ton of biochar applied. A single household using a gasifier stove can generate around 300 kg of biochar annually, which is enough to treat roughly 0.2 hectares at an application rate of 1.5 tons per hectare. To maximize effectiveness, farmers typically apply biochar directly to seeded rows.
