Sunlight supercharges soil superfoods: Boosting fertility and microbes with aged hydrochar

Degraded soils and the burgeoning challenge of agricultural waste pose significant hurdles to global food security. A recent study, published in Carbon Research, unveils a promising solution: using solar radiation to enhance hydrochar, a carbon-rich material derived from biomass, to create a more effective soil amendment. This innovative approach offers a low-energy pathway to transform materials like pig manure and mandarin peels into powerful tools for soil remediation.

The research team prepared hydrochars under varying hydrothermal carbonization temperatures (180 °C and 260 °C), then subjected them to simulated solar aging for 200 hours, including periodic wetting. Comprehensive characterization using advanced techniques such as FTIR, XPS, 3D-EEM, and ESI-FT-ICR MS was employed to track changes in the hydrochar's physicochemical properties and the composition of its dissolved organic matter (DOM). Soil microcosm experiments further evaluated the impact of these modified hydrochars on paddy soil for 45 days, assessing changes in soil properties and microbial communities.

Unlocking Hydrochar's Potential with Sunlight

The study found that solar aging significantly modified the hydrochars, particularly those produced at higher temperatures. Aging promoted the development of micropores and facilitated the transformation of oxygen-containing functional groups, such as C=O and C–O, through photochemical reactions. While solar aging reduced the total amount of DOM, it remarkably increased its molecular diversity, specifically enhancing the proportion of low-molecular-weight, bioavailable organic compounds like protein-like substances by 1.2% to 5.5%.

A Boost for Soil Health and Microbial Life

When applied to soil, the hydrochar amendments delivered impressive results. Soil organic carbon content increased by 53.3% to 110.0%, and total nitrogen rose by 14.2% to 28.5%. The aged hydrochar also selectively enriched beneficial microbial taxa, including Geobacter and Bacillus, and upregulated genes associated with carbon, nitrogen, and phosphorus metabolism. These changes collectively enhanced overall soil fertility and microbial activity, showcasing the profound impact of the treated material.

Deeper Insights into Nitrogen Dynamics

Notably, while aged hydrochar reduced ammonium nitrogen (NH₄⁺-N) content in the soil, the researchers clarified this as a positive outcome of enhanced nitrogen transformation. It points to a regulated shift in nitrogen cycling toward improved retention and reduced loss pathways, rather than a decline in overall soil nitrogen fertility. This molecular-level understanding of how solar-driven carbon structure evolution in hydrochars interacts with soil microorganisms provides a robust foundation for their application.

Suggested author quote for approval:

"Our findings underscore the remarkable potential of solar radiation as a low-energy modification strategy for carbon-based materials," states Professor Yanfang Feng from the Jiangsu Academy of Agricultural Sciences. "By understanding the molecular interplay between solar-aged hydrochar and soil microbiota, we can develop sustainable solutions that not only remediate soils but also contribute to carbon sequestration and advance precision agriculture."

The current research was conducted within the specific context of flooded rice systems. Future work will focus on field-scale validation, optimizing the parameters for solar aging, and systematically evaluating the broader ecological and economic benefits of these solar-aged hydrochars. This strategy holds significant promise for promoting the widespread application of carbon materials in sustainable soil remediation and nutrient management.

Corresponding Author: Yanfang Feng

Original Source: https://doi.org/10.1007/s44246-026-00277-1

Contributions: All authors contributed to the study conception and design. Lili He and Yahui Ji contributed equally to the study conception, design, investigation, data analysis, and the writing of the original draft. Detian Li and Yuying Wang contributed to material preparation, investigation, data collection, and analysis. Haohao Lyu, Bingyu Wang, Bingfa Chen, Xiangyu Liu, and Chengrong Chen contributed to experimentation, resource provision, and data validation. Bin Guo and Neng Li contributed to supervision, project administration, and resource support. Yanfang Feng oversaw the project, acquired funding, supervised the research, and reviewed and edited the manuscript. All authors participated in reviewing and revising the manuscript and approved the final version.