Soil minerals slow the downward movement of biochar-derived carbon during gentle rainfalls

Researchers from Kunming University of Science and Technology have discovered that certain soil minerals can trap dissolved organic matter released from biochar, keeping more carbon in the soil and potentially enhancing its long-term storage. Their study, published in Biochar, reveals that low-intensity rainfall helps retain this dissolved carbon within mineral-rich soils, limiting its downward movement and loss.

Biochar, a charcoal-like material made from plant matter, is increasingly used to improve soil fertility and sequester carbon. Yet as biochar ages, it can release dissolved organic matter (DOM) that may move through the soil during rainfall, reducing its carbon storage benefits. To better understand this process, the research team simulated rainfall on soil columns containing biochar and two common soil minerals, hematite and montmorillonite.

The experiments compared the behavior of dissolved organic carbon during both high- and low-intensity rainfall. The team found that montmorillonite, a type of clay mineral, was especially effective at capturing DOM, reducing its migration by over 80 percent compared to soils made mostly of sand. Moreover, under low-intensity rainfall, DOM concentrations increased gradually and were more likely to be adsorbed by minerals. In contrast, high-intensity rainfall quickly flushed DOM through the soil.

“Low-intensity rainfall gives dissolved organic matter more time to interact with soil minerals, which helps trap carbon near the surface,” said Professor Bo Pan, senior author of the study. “This mineral retention process is especially strong in soils rich in montmorillonite.”

Fluorescence analysis showed that humic-like substances within the DOM were preferentially adsorbed by minerals, while smaller, aromatic compounds tended to move more freely through the soil. This selective adsorption may influence both soil carbon storage and fertility, since humic substances are important for soil health.

The findings highlight the importance of mineral composition and rainfall conditions in determining how biochar-derived carbon behaves in soil systems. In environments dominated by clay minerals and exposed to frequent light rainfalls, more carbon is likely to remain sequestered in the soil rather than leaching downward.

This work provides new insights into the long-term fate of biochar in agricultural and natural soils and offers guidance for managing biochar applications under different climate conditions.

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Journal Reference: Li, F., Duan, X., Zhou, J. et al. Inhibited vertical mobility of biochar-derived dissolved organic matter under low-intensity rainfall: role of mineral retention. Biochar 7, 99 (2025). https://doi.org/10.1007/s42773-025-00484-w  

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About Biochar

Biochar is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field. 

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