Biochar in Agriculture More Complex Than Many Think, Says SLU Researcher

Swedish University of Agricultural Sciences aims to develop practical guidelines for farmers as biochar adoption faces technical and economic challenges

The use of biochar in agriculture is attracting growing interest for its potential to improve soil quality, increase water-holding capacity, and recycle valuable nutrients. However, according to a researcher at the Swedish University of Agricultural Sciences (SLU), biochar should not be viewed as a universal solution for increasing crop yields.

Helene Larsson Jönsson, a researcher at SLU's Department of Biosystems and Technology, is leading research efforts to better understand how different types of biochar interact with agricultural crops. Her goal is to develop practical guidelines that can help farmers make informed decisions about biochar use.

“Biochar is a bit more complex than many think,” Larsson Jönsson said.

Biochar is produced through pyrolysis, a process in which biomass is heated in an oxygen-free environment. Feedstocks can include forestry residues, agricultural waste, compost materials, and sewage sludge from wastewater treatment plants.

According to Larsson Jönsson, one of the main challenges is that biochar properties vary significantly depending on the raw material used during production.

“There is quite a lot of discussion about biochar, and sometimes it is generalized a little too much,” she explained. “There is a big difference in properties depending on the type of biochar, for example whether it is made of wood, sludge or compost. Crops also respond very differently.”

As a result, no single biochar product can be expected to perform the same way across all agricultural systems.

Despite this complexity, Larsson Jönsson believes research can identify broader patterns that will allow farmers to benefit from practical recommendations.

“For biochar to become useful in agriculture, it must be possible to give general advice,” she said. “It cannot be a specific recommendation for every crop and every type of biochar.”

To achieve this, researchers are evaluating the effects of biochar on a range of crops over longer periods of time through field-based studies.

One crop of particular interest is potato. Larsson Jönsson hopes to include potatoes in future field trials because the crop requires substantial amounts of water and may benefit from biochar's water-holding capacity.

Today, however, the economic reality remains a major obstacle to broader adoption.

“Biochar is too expensive to be used by farmers on a larger scale,” she noted.

One possible solution, according to Larsson Jönsson, is the use of carbon credits. Under such a model, companies could finance biochar applications as part of their climate compensation efforts, while farmers would gain access to the material without bearing the full cost.

“A company can pay for the biochar as climate compensation, since carbon is stored in the soil in this way,” she said. “That way the farmer gets the biochar for free.”

Beyond carbon storage, Larsson Jönsson also highlights the environmental benefits associated with nutrient recycling. Phosphorus contained in biochar can help reduce dependence on synthetic fertilizers, while converting waste materials into useful agricultural products supports circular resource management.

One area she finds particularly promising is the use of sewage sludge-derived biochar.

“What I find most exciting right now is whether sludge biochar, that is, from wastewater treatment plants, can be used in agriculture in a safe way,” she said. “It would be a major societal gain if we could make biochar from it.”

The ongoing research at SLU seeks to provide the scientific foundation needed to support practical biochar use in agriculture. By improving understanding of how different biochars perform under different conditions, researchers hope to move the technology from experimental applications toward broader agricultural adoption.