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Overall, compost and vermicompost represent the most sustainable solutions for promoting stable carbon
sequestration and long-term soil health in Mediterranean and similar agroecosystems. Future studies should
focus on long-term field trials, deeper humic fraction characterization, and microbial functional profiling to
strengthen predictive models of carbon stabilization under different climate and management scenarios.

Although this study provides strong evidence of carbon stabilization via humification, the experimental
period (two years) limits conclusions about long-term persistence. Future research will focus on: (1)
extending monitoring to 5-10 years to evaluate the stability of HA and humin fractions; (2) including humin
characterization, as it is often the most stable component of HSs; and (3) exploring how HA/FA and E4/E6
ratios evolve under different cropping systems, soil management practices, and climatic conditions, and how
these indices correlate with deep-soil carbon sequestration.

DECLARATIONS

Acknowledgments
The authors express their gratitude to the Orfei Farm for providing both their land and personnel for the
open field experiments.

Authors’ contributions
Methodology, data collection and analysis, writing - original draft: Muscolo, A.; Maffia, A.
Conceptualization, writing - review and editing: Maffia, A.; Muscolo, A.; Marra, F.
Project administration, supervision, and funding acquisition: Muscolo, A.
Methodology: Maffia, A.; Battaglia, S.; Marra, F.; Mallamaci, C.
Data collection, writing - review and editing: Maffia, A.; Battaglia, S.; Marra, F.; Mallamaci, C.
Data collection, writing - original draft: Muscolo, A.; Maffia, A.
Review and editing: Muscolo, A.; Maffia, A.; Marra, F.;

Availability of data and materials
Data in this study are available from the corresponding author upon reasonable request.

Financial support and sponsorship
This research was funded by the Italian Ministry for University and Research (MUR) under Project
CN_00000022, “National Research Centre for Agricultural Technologies - Agritech” and “Solutions for Soil
Quality Assessment and Protection” 3.2.1.

Conflicts of interest
All authors declared that there are no conflicts of interest.

Ethical approval and consent to participate
Not applicable.

Consent for publication
Not applicable.

Copyright
© The Author(s) 2026.

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