Several studies now show the sustainability benefits of biochar. But a new meta analysis reveals how much more could be gained for crops and climate, if farmers keep applying biochar to their land over the long term.
Farmers who keep up this habit for years can increase crop yields by on average 10%, and cut farming-associated emissions by 20%, the new analysis finds, drawing on evidence from over 400 studies.
In fact on a global scale, its sustained use could offset 4.6% of global CO2 emissions from fossil fuels, the PNAS paper showed.
The analysis brought together a pool of 438 studies on biochar, a carbon-dense soil-enricher made by burning agricultural waste materials like straw at high heat without oxygen. Dozens of studies included in the analysis cataloged its effect over longer periods of four years and more. The research took place across various geographies and soil types, and focused primarily on farms of rice, wheat, and maize.
The first result that leapt out from the analysis was that steady, annual biochar application increases crop yields on average by 10.8%, and most interestingly, this effect held over time: studies showed that at five years or more, average yield increases attributed to biochar remained at 10.7%.
These gains were apparent across soil types, but sandy and loam soils in particular experienced a striking average yield surge of 42% at the five-year mark. This suggests that short-term studies on biochar might not reveal the cumulative benefits of biochar and shows the value of tracking its benefits over time.
Out of the grain crops surveyed, dryland crops like maize and wheat showed higher yield gains of up to 13% on average thanks to biochar, compared to rice. That’s because in the saturated soils of rice paddies, biochar is less able to clump together and form nutrient-retaining aggregations that help feed the crops.
The analysis showed that biochar also locked in large amounts of nitrous oxide emissions from fertilizers, reducing those emissions by an average 21.4% with repeated applications, by encouraging the growth of nitrogen-fixing microbes in the soil.
Biochar also substantially brought down methane emissions on rice paddies by 13.5%, due to increased aeration of the wet soil, which suppresses the growth of methane-producing microbes. It also raised soil organic carbon levels by a striking 52.5%.
Compared to these results, on farms where biochar was applied just once its effects dwindled after about three years. So the key lies in its repeated annual application on farms.
Curious to see how these benefits would extrapolate to crops and climate on a global scale, the researchers carried out a thought experiment. If 70% of all straw was converted into biochar and put into the soil, how big would the benefit be?
This amount of biochar would boost crop yields by 190 million tons, which is equivalent to a third of the US’s annual grain production. Subtracting the emissions produced by biochar production, transport, and application, the researchers determined that the straw biochar would still be able to lock away 1.84 billion metric tonnes of CO2-equivalent per year.
That’s 4.6% of global carbon dioxide emissions—a startling achievement for something as simple as waste straw. This carbon-reduction potential could be even higher if biochar was made using renewable sources instead of fossil fuels.
Biochar offers an inherently simple solution to the twin challenges of food production and climate. But to make it truly effective, it needs to be widespread, and for that, farmers need to be helped by government subsidies and other financial support mechanisms over the initial cost hurdles of producing it and applying it to their land, the study’s author’s argue.
In short, biochar is a solution that is both scalable and sustainable, they add say, and it sits quite literally at our fingertips. “These results position biochar as a critical climate mitigation tool.”
Yan et. al. “Sustained benefits of long-term biochar application for foodsecurity and climate change mitigation.” PNAS. 2025.
Image: ©Anthropocene Magazine
