Biochar helps farmland soils withstand extreme rain and drought by steadying carbon loss

Researchers led by Yue Pan at Shenyang Agricultural University tested how swings between wet and dry conditions affect soil organic carbon breakdown in a clay loam Alfisol from Northeast China, and whether biochar can soften these impacts. The team incubated soils for 90 days under three moisture patterns and three levels of corn straw biochar to mimic the more extreme rainfall expected under climate change.​

The study showed that stronger moisture variability sped up soil organic carbon decomposition, increasing cumulative carbon dioxide release by up to 17.2 percent compared with constant moisture. At the same time, fluctuating moisture boosted soil microbial activity and shifted the balance of bacterial groups that drive carbon cycling.

Climate change is already increasing the frequency and intensity of extreme rainfall events in many parts of the world, especially across Asia. These shifts translate into more frequent drying and rewetting of agricultural soils, which can disrupt soil structure and cause pulses of carbon dioxide as microbes rapidly consume newly exposed organic matter.​

In the experiment, the highest moisture variability treatment produced the greatest soil carbon losses, while even moderate variability still raised decomposition compared with stable conditions. The authors also observed that an initial burst of carbon dioxide after rewetting gradually faded as soils experienced repeated wet dry cycles.

Biochar is a charcoal like material made by heating crop residues or other biomass in low oxygen conditions, and is widely promoted as a tool to improve soils and store carbon. In this study, adding corn straw biochar changed both the physical structure of soil and the behavior of its microbial communities under variable moisture.​

“Biochar did not stop soil carbon from decomposing, but it helped the soil system become more resilient to water stress,” said lead author Yue Pan. At a moderate application rate, biochar increased the share of larger, more stable soil aggregates by about 19 percent and reduced the finest clay fraction by roughly 23 percent, making carbon less exposed to rapid microbial attack.

To track soil life, the team used phospholipid fatty acids as biochemical fingerprints of microbial biomass and different microbial groups. Moisture variability raised total microbial lipids by about 30 to nearly 40 percent compared with constant moisture, indicating more active microbial communities under fluctuating conditions.​

However, these communities changed in composition: the ratio of Gram positive to Gram negative bacteria increased under variable moisture, reflecting a shift toward microbes that tolerate stress and may use carbon differently. Biochar addition lowered the ratio of fungi to bacteria, likely because the alkaline biochar and possible contaminants were less favorable to fungi, further reshaping the pathways through which carbon moves in soil.

The study links faster carbon loss under moisture swings to both breakdown of soil aggregates and microbial shifts, highlighting that physical and biological processes are tightly intertwined. Where moisture variability increased the smallest soil particles that expose labile carbon, carbon dioxide release also rose, especially when microbial biomass and stress tolerant bacteria were abundant.​

“Managing how carbon is protected in soil requires thinking about structure and biology together, not in isolation,” Pan said. The results suggest that carefully managed biochar use, especially at moderate doses, can reinforce soil aggregates, buffer moisture stress for microbes, and partially offset the extra carbon losses driven by more erratic rainfall.​

Because the work was done under controlled laboratory conditions, the authors caution that field trials across different climates and cropping systems are needed to confirm long term effects. In real fields, plant roots, changing temperatures, and complex weather patterns will interact with biochar and moisture variability in additional ways.​

Future studies will aim to disentangle how different biochar types, application rates, and irrigation or rainfall regimes jointly influence soil carbon storage and greenhouse gas emissions. By clarifying these mechanisms, researchers hope to offer practical guidance for farmers and policymakers seeking to build more resilient, climate smart agricultural soils.​

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Journal Reference: Pan, Y., Tan, T., Ren, R. et al. Soil organic carbon decomposition in response to moisture, microbial communities, and biochar addition in Alfisols. Biochar 8, 5 (2026).   

https://doi.org/10.1007/s42773-025-00513-8  

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About Biochar

Biochar (e-ISSN: 2524-7867) 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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