A new study shows that hydrochar, a carbon-rich material made from wet biomass, can improve soil structure and help soils store more carbon more effectively than several common organic amendments.
Healthy soil depends on two closely linked foundations: stable soil aggregates and sufficient soil organic carbon. Together, they help soil retain water, cycle nutrients, support plant roots, and resist erosion. Yet many agricultural soils remain carbon-deficient, and commonly used amendments such as straw, manure, and conventional biochar do not always improve both soil carbon storage and soil structure at the same time.
Now, researchers report that hydrochar may offer a promising dual solution. In a microcosm incubation study published in Biochar, the team compared hydrochar with maize straw and straw-derived biochar in purple soil, a widely distributed agricultural soil type in China. They also tested hydrochars made from different feedstocks, including maize straw, pig manure, and Zanthoxylum stalks.
"Our results show that hydrochar is not just another carbon amendment. It can actively help rebuild soil structure while also increasing soil carbon storage," said corresponding author Ran Xiao. "This dual function is especially important for carbon-deficient croplands where both fertility and physical stability need improvement."
Hydrochar is produced through hydrothermal carbonization, a process that converts wet organic biomass into a carbon-rich solid under moderate temperature and pressure. Unlike conventional biochar, which is produced by dry pyrolysis at higher temperatures, hydrochar often contains both labile carbon fractions that can stimulate microbial activity and more stable carbon fractions that can persist in soil.
In the study, hydrochar treatments substantially increased the proportion of macroaggregates, the larger and more stable soil particles that protect organic carbon from rapid decomposition. Hydrochars also improved mean weight diameter, a key indicator of aggregate stability, and increased soil organic carbon compared with the untreated control. Among the feedstocks, Zanthoxylum stalk-derived hydrochar showed particularly strong performance, delivering high carbon retention and strong improvements in aggregate stability.
The researchers found that the mechanisms behind these benefits were not driven by carbon content alone. Dissolved organic carbon, microbial activity, lignin-derived compounds, and the balance between labile and recalcitrant carbon fractions all played important roles. Hydrochar-originated carbon was mainly stored as particulate organic matter and accumulated in macroaggregates, suggesting that physical protection within soil structure helped stabilize newly added carbon.
Feedstock selection also mattered. Pig manure-derived hydrochar supplied more nutrients and promoted microbial biomass carbon, while stalk-derived hydrochar was more effective for carbon retention and soil aggregation. This means hydrochar production could potentially be tailored for different agricultural goals, such as improving fertility, increasing carbon storage, or enhancing soil structure.
"Choosing the right feedstock is critical," said corresponding author Xiaoxuan Su. "A manure-based hydrochar may be useful when nutrient supply is the priority, while a lignocellulosic stalk-based hydrochar may be better suited for long-term carbon sequestration and aggregate stability."
The findings point to a practical opportunity for sustainable agriculture: transforming agricultural and livestock residues into targeted soil amendments. By converting waste biomass into hydrochar, farmers and land managers may be able to improve soil quality while contributing to carbon management.
Although the study was conducted under controlled microcosm conditions, the authors note that it provides mechanistic evidence for future field trials. The work suggests that hydrochar could become a customizable amendment for climate-smart soil management, helping croplands store more carbon, form stronger soil aggregates, and support more resilient agricultural systems.
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Journal Reference: Sun, L., Wang, J.J., Wei, S. et al. Hydrochar as an effective amendment for enhancing soil aggregation and carbon sequestration: evidence from comparative microcosm experiments. Biochar 8, 69 (2026).
https://doi.org/10.1007/s42773-025-00547-y
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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.
