On-Farm Production and Use of Biochar: What were the practical challenges?

In the first blog of this series, we explored the motivations for introducing biochar into sustainable farming practices. In this second of three blogs, we share insights into the processes involved in on-farm biochar production and application and explore the challenges identified along the way. As this blog focuses on the farmer experience of working through the process of producing and applying biochar on-farm, it is primarily written from the perspective of the farmers with whom the Climate Spheres’ UK team collaborated at Aqualate Farms.

1. Gathering materials for biochar production (November 2023)

The Aqualate Farms team processed naturally fallen oak boughs for the biochar, cutting sections to the required size with a small chainsaw before loading it into a high sided farm trailer. This required significant labour to process the timber down to optimum sized pieces for the kiln and this stage should not be underestimated in terms of either time or fuel costs in the production process. Due to wetter than usual conditions over the past year, the wood was still too wet to be made into biochar so it was left under cover in a barn to dry out. While we had allowed time in our timeline for drying, the burn was delayed by over a month as a result of the dampness with the wood drying for a total of 3 months. In future projects, we would want to include more contingency time here.

2. Biochar production (February 2024)

After nearly 3 months under cover, the wood had dried sufficiently to go in the kiln. Next we needed to construct the kiln from parts and load it with approximately 6 tonnes of oak. Assembling and filling the kiln was heavy work and we needed to bring over more farm workers to help with this. Some logs were still too large, creating too much air space in the kiln so had to be broken down further. We arranged smaller logs at the bottom as kindling, and larger logs through the rest of the kiln. We used the tractor to dig a load full of sandy soil, and used some of this to block the air gaps around the bottom of the kiln. We lit the kiln using a gas bottle and pipe fed through one of the vents, and let it burn for approximately 24 hours, moving the chimneys round a few times to ensure an even burn. 

Once the smoke had mostly stopped, we blocked off the gaps and chimney vents with more sandy soil and left the kiln for a further 48 hours for the biochar to cool. Although we had guidance from a biochar expert, we ourselves were unfamiliar with using the kiln and felt uncertain in our timings and in how we would spot any early indicators of problems. Thankfully, the burn seemed to go according to plan. At this point we were still unclear on how much biochar would be coming out, making it hard to plan for the workload for removing it.

3. Emptying the kiln (March 2024)

Once the biochar was fully cooled, we emptied the kiln and transferred the biochar into tonne bags using a tractor loader. We wanted to know the bulk weight of the biochar and considered a few options given the farm equipment that we had to hand. In the end, we weighed the filled bags on a set of hanging scales hooked onto the tractor tines. A full kiln of oak had produced approximately ½ tonne of biochar. We sent a 1 kg sample to be tested by Eurofins. The biochar test results came back with no red flags on content or composition, however it is not immediately clear how the more detailed results should be interpreted. It was important to have both project partners and known experts that could review the results to give us confidence that the biochar was suitable for use. This coming back positively, our biochar was ready for crushing down and charging with nutrients.

5. Spreading the biochar mix (May 2024)

The biochar and manure mix was spread later than originally intended, due to the land still being too wet to use heavy machinery. The main challenge here was how to spread a small volume. The quantity was too small to use our full size spreader, however we were able to borrow a small 1 tonne spreader from a neighbour. We aimed to approach the regulatory limit of 1 tonne per hectare, while staying comfortably below.

After spreading, we passed over with a disc drill partly to ensure that the biochar was at least partially incorporated into the soil to reduce the risk of smaller particles blowing away. The wetting and mixing with manure will also have helped to reduce this risk. A herbal ley seed was then sown over the site.

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