Biochar in the Field: What We Learned from Real Farm Trials in Cornwall
Lettuce yield being measured post harvest having been planted with biochar
At Restord, we believe that good ideas must be tested in the real world. That is why we were excited to work with Ewan Swan, an MSc researcher from the University of Plymouth, to run field trials on biochar during his placement with us and as part of his masters dissertation.
The study set out to answer two simple but important questions:
Can biochar improve crop growth and soil health on UK farms?
Can biochar help reduce nutrient pollution from farmland entering streams and rivers?
Why Biochar Matters
Biochar is a charcoal-like material made by heating wood or other plant matter without oxygen. When added to soil, it can improve structure, hold water and nutrients, and support plant growth. It also stores carbon in a stable form for hundreds of years.
Farmers in the UK are under pressure to improve fertiliser use, improve soil health and protect local rivers from agricultural runoff. Biochar could help on all three fronts.
How the Trials Worked
Ewan led two field trials at farms near Liskeard, Cornwall:
Both trials used Restord biochar, made locally from waste wood from Cornwall and environs.
Trial 1: Biochar Improved Lettuce Growth
At Mora Farm, biochar was mixed with chicken manure and added to soil at different rates. The experiment tested five treatments: a control (no inputs), a manure-only plot, and manure combined with 2%, 4%, and 8% biochar by soil mass. These correspond to approximately:
2% → 3.9 kg m² ≈ 15.8 t acre⁻¹
4% → 7.8 kg m² ≈ 31.6 t acre⁻¹
8% → 15.6 kg m² ≈ 63.2 t acre⁻¹
These rates assume a 15cm tillage depth and an average soil bulk density of 1,300 kg m⁻³, consistent with typical vegetable-growing soils.
Biochar was incorporated before planting to ensure even distribution through the soil layer in alignment with Mora farm’s existing practices. Manure was applied at the same rate across all amended plots to isolate the biochar’s effect, and lettuce was chosen for this experiment because it grows quickly and shows early changes in soil conditions.
Applying biochar and manure to lettuce bed
What Happened?
Biochar improved soil moisture retention and electrical conductivity (EC) across all treatments. These changes indicate better water-holding capacity and increased nutrient availability. The effects were most pronounced at the 2% and 4% application rates, where soil moisture was consistently higher during dry periods and EC levels indicated a balanced nutrient environment.
The 2% treatment (~3.9 kg m²) produced the highest total biomass yield, showing large lettuce and roots compared with the control and manure-only plots. The 4% and 8% rate also performed significantly better than the control and manure only.
Lettuce yield being measured post harvest
Biochar amendment rate vs total biomass
It’s worth noting that the 8% application rate offered no further yield advantage, suggesting that beyond a certain point, adding more biochar does not translate into better results, an important consideration for practical on-farm use.
“We found the sweet spot was between 2% and 4% biochar. That was enough to improve soil and help the plants without ‘overdoing’ it.”
- Ewan Swan, Researcher
Trial 2: Biochar Helped Reduce Phosphate in Water
While the first trial focused on crop yield and soil quality, the second explored how biochar might help protect waterways from agricultural runoff. Nutrient leaching - particularly phosphates and nitrates - is a persistent challenge in UK farming, leading to eutrophication in rivers and lakes.
To test biochar’s filtration potential, we set up a simple but effective system using mesh bags filled with Restord biochar placed at three points in a small stream running through Bokenna Farm. Water samples were collected weekly for analysis at upstream, midstream, and downstream locations.
The results were telling:
Phosphate concentrations decreased by roughly 25% between upstream and downstream readings where biochar filters were installed.
Nitrate concentrations remained largely unchanged, indicating that while biochar can effectively adsorb phosphorus compounds, it may need further enhancement to capture nitrates.
The filters held up well under heavy rainfall, demonstrating physical stability even when water flow increased.
This suggests biochar has potential as a low-cost buffer to help protect streams from farm nutrients.
Water filtration trial in Bokenna farm
Together, the two trials illustrate biochar’s versatility across agricultural and environmental systems. On the soil side, it can improve crop resilience and moisture balance; on the water side, it’s capable of capturing excess nutrients that would otherwise leave the field.
Carbon Benefits Included
Every tonne of Restord biochar locks away around three tonnes of CO₂ equivalent, based on testing from an independent lab. The biochar used in the trials passed European Biochar Certificate stability standards, with a H/C ratio of 0.34, which means it stores carbon safely for the long term.
What This Means for Farmers
The trials showed that biochar is:
✅ Useful in organic and regenerative farming
✅ Strong results from a 2 - 4% application rate with manure or compost
✅ A long-term soil improvement tool
✅ Able to support water quality efforts
✅ A carbon removal solution that works on real farms
Next steps include testing biochar with more crops, soils and farms across the UK. There is also interest in improving biochar filters to tackle nitrates as well as phosphates.
Lessons we’ve learnt
Conducting trials is time consuming and can be expensive. We were very lucky to have the time and knowledge from a dedicated student
We iterated a lot from the first trial ideas. Be open to accepting that your first trial idea may not be the right one
These are small scale field trials which is to say that results would most likely change as you scale these applications up.
We would like to test lower application rates i.e. 0.5%, 1%, 1.5% to test biochar’s effectiveness at lower levels. Scaled up, 2, 4 & 8% application rates equates to a large amount per acre and higher than what is currently allowed in the UK under EA guidance.
PLEASE NOTE:
This work summarises findings from an MSc dissertation project rather than a peer-reviewed journal article. We aimed to apply sound methods and report results transparently, but these are small-scale field trials and the findings should be interpreted with appropriate caution pending further research.
Download the Full Research Report
This blog shares highlights only. The full report includes:
✔ Full data charts
✔ Soil and water measurements
✔ Nutrient analysis
✔ Field photos
✔ Practical recommendations
The report is in the works. Tell us here if you’d like the report and we’d send it to you when it’s ready.
Contact us if you'd like help trying biochar on your farm or would like to take part in future trials.
