Biochar has been used by farmers around the world for millennia - but it could offer a way for dairies to reduce their problematic carbon emissions.
Biochar is a charcoal-like substance which is produced by burning vegetable matter in a controlled process called pyrolysis which releases little to no fumes.
Biochar captures carbon into a stable form that can’t easily escape into the atmosphere.
New research has shown that adding biochar to a dairy’s manure-composting process reduces methane emissions by up to 84%, according to a study by University of California, Merced.
Scientists believe that biochar – commonly used by gardeners – could be an important way to stop gases such as CO2 being released from soil, according to the World Economic Forum.
Life and environmental sciences professor Rebecca Ryals said: "This is a wonderful example of an untapped climate solution.”
"Biochar reduces pollutant emissions from open burning of biomass and methane emissions from decaying biomass."
"Composting the solid manure isn't common practice, but if we go from stockpiling to composting, now we've gone from a carbon source to a carbon sink.
"Composting in and of itself is a very climate-beneficial practice. And you can basically double your impact by adding a little bit of biochar into that compost."
In California, where the study took place, dairy manure is one of the largest sources of organic waste.
Farmers flush the waste from their barns and the liquids go into large, uncovered ponds, while the solids are piled up.
Sometimes farmers cover the ponds to capture methane gases, which are fed into generators and burned to produce electricity.
Fourth-year graduate student Brendan Harrison said, "It's actually a pretty good way to reduce methane emissions, given the technologies that are currently available.”
"But what it leaves out are all the solids, which is a problem because basically they either spread it on adjacent fields just to get rid of it or they store it in big mounds.
"You can see them when you go past a dairy, covered with white plastic held down with tires. They can build up so much heat they spontaneously catch fire."
The study looked at composting the manure with biochar instead of stockpiling it.
Mechanical engineering professor Gerardo Diazio said that biochar also improves the composted manure so that it makes a better fertiliser for farmers to use on other parts of their land.
"We were looking at how to reduce emissions but also how to provide some benefit to the community, especially underserved communities," Diaz said.
"We looked at the possibility of developing a mobile unit that we could take to different sites to process some of the material there."
The study suggested small farmers would be able to use the improved fertiliser on their own farms to increase yield or sell it to others who need it.
Watch: Marine heatwaves - a sea in flames