Information for Farmers

Biochar is a carbon-rich substance produced by pyrolysis. Pyrolysis is the thermal decomposition of biomass at a very high temperature and under oxygen-deprived conditions. Three by-products are produced: biochar (solid), bio-oil (liquid) and syngas (gas).

Biochar can be produced from a range of organic sources including organic waste that has no other use. It can be produced from virgin wood, domestic green waste, agricultural waste (including crop residues and livestock manure) and forestry waste, but biochar cannot be produced from waste wood due to contaminants which may have detrimental effects on plant growth, groundwater and the food chain.

At the Biochar Demonstrator, our plan for agricultural field trials is to use biochar supplied from a manufacturer that uses virgin wood as the source material for the biochar.

Biochar made from agricultural and forestry residues can be applied to soils and is potentially a means of sequestering (locking up) carbon for thousands of years, thereby removing carbon dioxide from the atmosphere. It can also act as a soil conditioner by increasing pH of acidic soils, improving water holding capacity, modifying nutrient exchange between plant and soil, and improving soil aeration and structure, especially in heavy soils. These are beneficial to plant health, yield and can minimise fertiliser losses.

Effects on plant growth can be seen within 1 year due to the addition of nutrients from the biochar (e.g. P and K). Generally, most beneficial effects are seen in the first few years. In some cases, no added benefit to crop growth is seen, but benefits are seen in the soil (e.g. in terms of increasing soil C content).

However, biochar has been shown to have both positive and negative effects on the soil. The negative effects may include to be reduced soil-applied pesticide and herbicide efficiency, washing off of biochar into watercourses under heavy rain, wind erosion of biochar dust. In summary – there is continuing uncertainty, which is why trials are of the upmost importance.

Biochar costs between £400 and £1000 per tonne wholesale. The retail cost is considerably higher for biochar products for the garden purchased typically in litre quantities. For farmers taking part in our trials, the Biochar Demonstrator is suppling biochar at no cost to the farmers.

The best time to apply biochar to arable fields is before cultivation or crop establishment. For harvested crops like winter wheat, this would mean applying the biochar in the previous autumn.

It is possible to apply biochar with a conventional Farm Yard Manure (FYM) spreader if the biochar is mixed with FYM prior to application. It is also possible to apply biochar with specialist equipment (e.g. lime spreader) directly on to land.

For farms that want to apply biochar with FYM, and if they have the equipment, then farmers can apply this themselves. For farmers who want to apply the biochar without FYM a lime spreading contractor can do the application.

For farmers working with the biochar demonstrator, we would arrange an appropriately timed delivery of biochar to your farm and any contractors needed for application.

Biochar lasts for hundreds or thousands of years in the soil. Most forms of biochar degrade very slowly so will be retained in the soil during a human lifetime. However, depending on how biochar is produced movement of biochar may occur over shorter timescales. Once added, it is almost impossible to remove the biochar from the soil.

Normally, farmers apply between 10 to 20 tonnes of biochar per hectare, however, trials have shown that up to 100 tonnes per hectare can be added over several years to a field with no negative consequences on plant growth and soil health. However, the Environment Agency currently only allows up to 1 tonne of biochar per hectare to be spread over any 12 month period.

Adding biochar to cultivated land can in principle contribute to climate change mitigation.

Biochar aims to mitigate climate change through the capture and storage of atmospheric carbon, whilst also increasing the stock of soil carbon in agroecosystems. There is also the potential for decreases in nitrous oxide emissions from nitrogen fertiliser applications. A typical soil in the UK contains 70 t C ha-1 in organic matter; adding biochar at 10 t ha-1 therefore increases the C content of the soil by 10% as the biochar contains ca. 70% carbon.

Gardeners are already using biochar to increase water and nutrient retention in soils, to improve drainage and aeration of soils, and to improve plant health. The Royal Horticultural Society (RHS) provides advice on its use. Gardeners in the UK can purchase biochar from companies including Carbon Gold, SoilFixer, and The Oxford Charcoal Company.

In agriculture, biochar has been used in a trial by Innovative Farmers. In this trial, biochar was fed to beef cattle to evaluate the effect on manure ammonium and nitrate content, ammonia emissions, worm burden, pH, and the resulting manures’ effect on grass growth. The trial was not able to detect any changes to cattle health or improvements to grass growth. In a three year field trial in Wales to evaluate the effects of biochar on soil quality and crop performance no negative impacts on crop growth, crop nutrition or soil quality were found following the application of biochar. Studies have also been undertaken with farmers in Norway, and Poland, in order to understand their knowledge and perspectives on biochar. The farmers in these studies were interested in biochar’s potential to improve soil quality and increase crop production.

The term ‘biochar’ appears to have been coined at the 2006 Pennsylvania Soil Conference where it was a topic of discussion. Whilst biochar seems a relatively new material, it has a long and complex history. Biochar is related to terras pretas, otherwise known as Amazonian Dark Earths. These soils are small areas (2 to 20 hectares) in the lowland regions of Amazonia which contain large amounts of black carbon from the incomplete combustion of organic materials. Terras pretas are not natural but were formed through human intervention. Indigenous people burnt wood in hearths, and the carbonised remains were applied to the soils enabling the terras pretas to form.

Attempts to recreate terra preta led to the Terra Preta Nova Project in 2002 and to the commercialisation of terra preta. Terra Preta Nova is an artificially produced soil which can be produced anywhere in the world through a technical process. Terra Preta Nova became connected to the idea of climate change mitigation and sustainable development, and moved the benefits of carbon sequestration and soil fertility from a local scale to a global focus. From 2006, the focus shifted from Terra Preta Nova to biochar.