Biochar, a carbon-rich material produced by heating organic materials in low-oxygen conditions (pyrolysis), is usually made from agricultural wastes. Due to its porous structure and physicochemical properties, it can boost crop growth, enhance carbon sequestration and reduce non-CO2 greenhouse gas (GHG) emissions.
However, most evidence supporting biochar’s benefits comes from short-term experiments (<3 years), leaving uncertainty about long-term effects, especially with repeated annual applications. Is the magic of biochar application in ensuring food security and mitigating climate change sustained over the long term? What happens in the long term if biochar is applied annually or once at large quantity?
Recent research led by Professors YAN Xiaoyuan and XIA Longlong from the Institute of Soil Science, Chinese Academy of Sciences (ISSCAS), analyzing high-quality field experiment records from 438 studies addressed these questions, and the results were recently published in Proceedings of the National Academy of Sciences of the United States of America.
The study found that annual biochar application over four years or more not only sustained but often amplified its benefits, on average, boosting crop yields by 10.8%, reducing methane (CH4) emissions by 13.5% and nitrous oxide (N2O) emissions by 21.4%, and increasing soil organic carbon (SOC) content by 52.5% in global croplands. These findings were supported by annual consecutive data from 29 long-term field experiments. Single application showed weakened effects over time due to aging effect, but was still beneficial, with continued yields and SOC rise, and continued CH4 and N2O mitigation, albeit at a weakening trend.
“This result is exciting. We wonder how significant biochar’s potential could be for carbon sequestration and emission reduction in global farmlands under long-term application,” said YANG Jingrui, first author and PhD student from ISSCAS.
Based on current straw and biochar management practices, researchers estimated that converting 70% of straw into biochar for agricultural fields could boost global grain yields by 190 million tons annually and enhance carbon dioxide removal (CDR) potential by 2.01 Pg of CO2-eq annually—about 30% of China’s average annual grain yield from 2018 to 2021. After accounting for GHG emissions from biochar production (0.25 tons of CO2 per ton of biochar), the net CDR potential remained at 1.84 Pg of CO2-eq per year, offsetting about 4.6% of global fossil fuel CO2 emissions.
Researchers suggested that strategic deployment of biochar at multi-year intervals or with break periods between yearly applications could maintain its benefits cost-effectively while minimizing risks. Expanding field experiments and comparative trials across different soil types, climates, and cropping systems are crucial for refining application strategies, especially in determining optimal frequencies and rates.
While periodic biochar application tailored to local conditions can reduce costs and secure long-term advantages, the initial economic burden may deter risk-averse farmers. “Since farmers are unlikely to increase their input costs unless they’ve got solid proof that it’ll work, running large-scale demo trials in major grain-growing areas—like the North China Plain and the U.S. Corn Belt—is key to proving that using biochar makes economic and environmental sense,” said YAN Xiaoyuan, the leading scientist of this work from ISSCAS.
Cost-benefit analysis showed that the net economic and environmental benefit, driven by enhanced crop yields and decreased GHG emissions, could compensate for roughly 81% of biochar procurement costs. This ratio could rise further when considering the mitigation of reactive nitrogen losses. Government-backed subsidy programs are essential to encourage farmers to adopt biochar in their land management strategies.
Long-term benefits of biochar application on food security and climate change mitigation (Image by Yan Xiaoyuan's research team).
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