Abstract
Biochar reshapes soil composition for years, yet most evidence comes from short-term, single-element laboratory incubations, leaving multi-element dynamics in tropical soils poorly resolved. We tracked 11 elements in longan-wood biochar and biochar-amended Ultisols over three years after a single field application, combining micro-XRF with SEM–EDX (one Map Sum Spectrum per group). Soil Fe and Al showed a non-linear response: both peaked at Year 1 (Fe 17.77 ± 3.93; Al 21.33 ± 1.88 wt.%; ~ 3.1- and 1.75-fold above control), fell at Year 2, then rose again at Year 3—a pattern invisible to single time-point studies, consistent with organo-mineral coating formation and reworking. Soil P stayed below detection despite annual fertilisation, indicating persistent Fe–Al phosphate fixation, while soil K peaked at Year 2 (1.82 wt.%). The biochars were Ca-rich (> 60 wt.%), acting as strong liming agents. EM-inoculated biochar showed higher surface carbon (92.7 vs. 77.6 wt.%), consistent with microbial biofilm deposition, though EM did not alter inorganic composition; a high Year-3 N signal (13.52 ± 23.42 wt.%) is a semi-quantitative artefact, not a reliable soil-N value. These findings reveal non-linear multi-element redistribution from a single biochar application and show the value of pairing bulk and surface analysis for long-term biochar–soil studies.
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Acknowledgements
The authors gratefully acknowledge the owners of all longan orchard plots for their kind cooperation and facilitation of this research. The authors also thank the Maejo IQS facility (Institute of Product Quality and Standardization, Maejo University) for access to the field-emission SEM and EDX facilities used in this study.
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Aumtong, S., Soongsoongnoen, P. & Wanwinit, D. Temporal dynamics of nutrient elements in biochar and biochar-amended soils over three years: a comparative micro-XRF and SEM–EDX study.
Sci Rep (2026). https://doi.org/10.1038/s41598-026-59314-z
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DOI: https://doi.org/10.1038/s41598-026-59314-z
Keywords
- Biochar aging
- Micro-XRF
- SEM–EDX
- Fe–Al redistribution
- Organo-mineral coatings
- Effective microorganisms
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