Could Drones allow for Biochar Application on Paludiculture Fields?
© Nottingham University
Jenny Rhymes, Lily McGuinness and Scott Dowell
The economic viability of paludiculture—farming on rewetted peat—remains uncertain. Unlike conventional farming, which relies on drainage to grow high-value crops like broccoli, paludiculture requires a shift toward different crops, often non-food varieties, that tend to be of lower market value. Additionally, productivity is generally reduced due to the waterlogged conditions. As a result, farmers may need to rely on alternative revenue streams, such as carbon credits from voluntary carbon markets, which are still underdeveloped. Furthermore, the upfront costs of converting farmland to paludiculture can be significant, posing another barrier to its widespread adoption.
Why biochar?
Biochar, a stable form of carbon created by heating biomass under low-oxygen conditions (pyrolysis), could help mitigate some of these financial challenges. With over 70% carbon content and high stability, biochar can enhance carbon sequestration, opening up revenue opportunities from voluntary carbon credit markets. Importantly, biochar feedstocks could be sourced from within the farm itself, using crop residues or materials from hedgerow management, minimizing costs for transport and production.
In addition to its carbon benefits, biochar could potentially increase crop yields. This boost in productivity could provide farmers with higher returns from the sale of paludiculture products, offsetting some of the revenue losses from transitioning to lower-value crops. Furthermore, biochar has been found to suppress methane emissions, one of the most potent greenhouse gases, a trade-off associated with rewetting. However, how biochar behaves specifically on peat under paludiculture conditions is still not fully understood, representing an important research gap that needs further exploration. This dual benefit of enhanced yields and methane suppression could make biochar an even more valuable addition to paludiculture systems, supporting both environmental and economic goals.
Can Drones Overcome Barriers to Biochar Application?
A significant challenge for paludiculture more generally is accessibility onto the land for essential farm tasks such as planting, harvesting, and applying soil amendments. Wet soils are difficult or even impossible to access with traditional machinery, here drones could come in as a potential solution.
We tested the feasibility of using drones for biochar application, utilizing AutoSpray Systems’ XAG P100 Pro. Equipped with an 80-litre granular hopper and capable of lifting up to 50 kg —ideal for biochar, as 80 litres of biochar weighs just 16 kg.
XAG P100 Pro | Specifications |
|---|---|
Max lift capacity: | 50 kg |
Max takeoff mass: | 110 kg |
Battery weight: | 7 kg each (x2) |
Spray base capacity: | 50 litres |
Granular hopper capacity: | 80 liters (suitable for granules, fine grass seed, or pellets up to the size of large grapes) |
Our first flight revealed some challenges, particularly with the moisture content of the biochar. The biochar was too wet, leading to "bridging," where the material clogged arching over the augers, preventing it from being fed to the spreader discs and stopping the application process. To resolve this, we had to optimize the moisture level—damp enough to prevent dust, which poses health and safety risks, but not so wet that it caused blockages. Achieving the right moisture balance is crucial, as permissions for spreading biochar require that the biochar is sufficiently wet to mitigate dust. Further trials are necessary to fine-tune this for various biochar types, ensuring that the biochar flows continuously to the spreader discs without causing delays.
Following this adjustment, we conducted calculations to assess the time involved. At a coverage rate of 1 tonne per hectare (current regulatory application rates per year), each flight (from takeoff to landing) took around 5 minutes, requiring 62.5 flights and approximately 5.2 hours to cover one hectare. For larger applications, the time commitment increases significantly. For example, a rate of 10 tonnes per hectare would require 625 flights, taking roughly 52 hours, and at 20 tonnes per hectare, 1,250 flights would be needed, totalling 104 hours.
While drones offer a promising solution for accessing wet peatlands, the financial viability of using them for biochar application remains questionable. With biochar currently valued at around €125 per tonne in voluntary carbon credits, the high costs associated with drone operations outweigh potential revenue, especially for large-scale applications. For this approach to be financially feasible, the value of voluntary carbon credits would need to increase significantly.
However, drones could still play a valuable role in overcoming accessibility barriers for other paludiculture farming activities, such as seed spreading, where the lighter weight of seeds makes this method more practical. There are already successful examples of drone-assisted seed spreading in practice, click here to read more. For now, applying biochar directly to the land, rather than from the air, appears to be the more cost-effective option for paludiculture.
