Trials have shown that adding relatively small amounts of biochar to soil can significantly increase the amount of nutrients essential for crop growth, boosting crop yield.

The charcoal-like substance is produced when biomass – animal and plant matter such as manure, food waste or wood – is heated up at very high temperatures without oxygen. Biochar improves local soil properties around roots, allowing the crop to access more nutrients, and also increases soil carbon storage, so can help mitigate climate change.

Black Bull Biochar (BBB), Scotland's Rural College and the UK Centre for Ecology & Hydrology (UKCEH) are assessing its effectiveness and practicality as an additive to slurry on dairy farms in a project funded by the UK Government’s Department for Energy Security and Net Zero. Unlike previous field trials that have spread a large amount of biochar on farmland, typically 10 tonnes or more per hectare, the new project has used just 0.5 tonnes per hectare, which would make it more practical to implement at scale within agriculture.

Initial results from the trials in Dumfries showed grassland plots with biochar and slurry contained 51% more carbon and 22% more nitrogen in the soil compared to the plots with only slurry applied. These two nutrients are essential for plant and soil functions.

Preliminary results in the trial showed there was a 16% increase in the amount of grass harvested, which is typically stored to provide winter fodder for livestock.

The scientists involved in the project say the initial findings suggest that the practice of low-dose, tailored biochar application holds substantial promise for improving productivity and sustainability on farms. 

“Results from the first year of the BBB field trials are really exciting as they demonstrate that in addition to storing carbon in the soil, biochar application to grassland has benefits for crop productivity and nutrient retention,” says Professor Jeanette Whitaker, Principal Scientist in Soil and Land Use at UKCEH. She adds, “We will continue to monitor the longer-term impacts of this innovative delivery system as the applications of slurry and biochar are repeated annually.” 

A separate project, led by UKCEH and funded by a £500,000 grant from Natural England, is identifying cost-effective methods for biochar application under paludiculture conditions, maximising the ability of lowland peat soils to remove and store carbon. 


*Edited on 25 June to clarify the role of the nutrients