In a new study published in the journal PNAS, researchers led by Jingrui Yang and Longlong Xia have clarified a long-standing debate about the long-term effectiveness of biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More. While previous research has largely focused on short-term trials (three years or less), this comprehensive analysis synthesizes data from 438 global studies to show that biochar’s benefits not only persist but can actually intensify over time with repeated annual applications. This is a crucial finding for farmers and policymakers looking for sustainable solutions to enhance food security and combat climate change.

The research directly addresses a key question: does the effectiveness of biochar fade over time? The answer depends heavily on the application strategy. The global dataset, which includes results from 29 long-term field experiments (4 to 12 years), reveals a significant difference between single and annual biochar applications. When biochar is applied annually, its benefits are sustained and even enhanced. Over a period of four to twelve years, this method led to an average increase in crop yields of 10.8%, with the yield benefits becoming more pronounced after five years of application, reaching a 10.7% increase. This sustained increase in yield is a powerful argument for the long-term economic viability of biochar.

The study also provides critical insights into biochar’s role in climate change mitigation. It found that long-term annual applications significantly reduced methane (CH4​) emissions by 13.5% and nitrous oxide (N2​O) emissions by 21.4%. These reductions were particularly notable in paddy fields for CH4​ and in upland soils for N2​O. The reductions in GHG emissions are attributed to biochar’s ability to stimulate beneficial microbial activity, promoting the conversion of harmful gases like N2​O to harmless dinitrogen (N2​). The paper emphasizes that these reductions become more pronounced over time, showcasing biochar’s value as a sustained climate solution.

One of the most compelling findings of the study is biochar’s impact on soil organic carbon (SOC) content, a key indicator of soil health and carbon sequestration. Long-term annual applications of biochar led to a remarkable 52.5% increase in SOC content on average. This effect was shown to be cumulative, with SOC increases becoming more pronounced over time, rising to 69.0% after three to five years and 83.5% after more than five years of application. The study highlights that this increase is due to biochar’s stable carbon content and its ability to promote the retention of plant and microbial carbon in the soil. In contrast, single applications showed an average SOC increase of 30.5%, which, while still significant, did not show the same sustained, compounding growth over time.

The study also delves into the factors that influence biochar’s effectiveness. It found that sandy soils showed greater increases in crop yields, with a jump from 11.4% in the first year to 42.1% after five years, suggesting that biochar’s ability to improve soil structure and nutrient retention is particularly beneficial in these soil types. Management practices are also critical, with higher nitrogen fertilizer rates (≥240 kg Nha−1) leading to greater and more stable yield increases (12.2% to 14.9%) when combined with annual biochar application. This underscores the importance of a holistic approach to agricultural management rather than viewing biochar as a standalone solution.

Ultimately, the research provides strong evidence that a strategic, long-term approach to biochar application is essential to unlock its full potential. The authors propose that applying biochar at multiyear intervals or with tailored break periods can sustain its benefits while minimizing potential risks and costs. The study concludes by estimating that converting 70% of global straw to biochar could increase global grain yields by approximately 0.19 Pg y−1 and remove 2.01 Pg of CO2-equivalent per year, positioning biochar as a critical tool for both food security and climate mitigation.

Source: Yang, J., Xia, L., van Groenigen, K.J., Zhao, X., Tia, C., Wang, W., Du, Z., Fan, M., Zhuang, M., Smith, P., Lal, R., Butterbach-Bahl, K., Han, X., Meng, J., Liu, J., Cai, H., Cheng, Y., Liu, X., Shup, X., Jiao, X., Pan, Z., Tang, G., & Yan, X. (2025). Sustained benefits of long-term biochar application for food security and climate change mitigation. PNAS, 122(33), e2509237122.