Farmers in the US can expect to see an increase in crop yield of between 4.7 and 6.4%, on average, if they apply biochar to their fields. A charcoal made from plant remains, biochar may recondition soils stripped of nutrients by hungry crops.
“Adding biochar improves soil quality, helps the soil store both nutrients and water and makes the soil a better media for plant roots,” says David Laird of Iowa State University, US.
Farmers often burn or plough the stalks and plant debris left after harvesting. If instead these remnants cook slowly in low-oxygen conditions, the resulting biochar can be reused as a soil conditioner.
Hamze Dokoohaki, then at Iowa State University, US, investigated where farmers in the US are likely to see benefits from biochar. Together with Laird and other colleagues, Dokoohaki collated data from previous studies to analyse the relationship between biochar application and crop yields.
“While there is no or little incentive for farmers to adopt most climate change mitigation practices, the potential yield increase following biochar application has made it a promising new climate mitigation strategy,” write the scientists in Environmental Research Letters (ERL). “Farmers will have to weigh the cost of applying biochar—which usually happens in the first year—with the increase in revenue triggered by higher yields in subsequent years. Thus, the ability to accurately predict crop yield response to biochar applications is critical to the development of a viable biochar industry and to the design of incentive programs to enhance biochar adoption and carbon sequestration.”
“Under current economic and regulatory conditions, biochar is not going to be profitable for most grain farmers,” says Laird.
But farmers working on poor quality soils and those growing high-value crops could still benefit. Applying biochar to maize tended to boost revenue more than using the technique on soybeans or wheat.
“The US southeast has highly weathered soils that are acidic and have low nutrient holding capacity,” says Laird. “These soils are anticipated to be very responsive to biochar, because biochar treatments can be engineered to help solve these problems.”
To be economically worthwhile for take-up by farmers across a quarter of US cropland, biochar would need to produce yield increases of over 6%, the team found. Covering one tenth of US cropland would need yield increases of 8.8% upwards.
If carbon taxes were introduced in the US, biochar would become far more economically viable.
With yield increases of around 5.5%, biochar application in the US would sequester enough carbon in soil to offset just over 0.5% of US greenhouse gas emissions, the results showed.
Worldwide, tropical and subtropical regions tend to have some of the poorest soil quality. Countries like China and India have a long history of burning crop residues, which forms a major source of air pollution. Switching to producing biochar could both reduce air pollution and significantly increase crop yields.
Dokoohaki, Laird and colleagues published the study in Environmental Research Letters (ERL).