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environmental benefits.

INTRODUCTION
Reducing the carbon footprint (CFP) of agri-food systems while sustaining soil health and improving
productivity is a global priority in the context of climate change and food security. Two complementary
research directions have emerged as central to this challenge: (i) robust CFP assessments, which quantify
emissions across the life cycle of agricultural inputs and practices, and (ii) analyses of carbon dynamics in
food production systems, which elucidate the mechanisms of carbon sequestration, stabilization, and
turnover in soils. Against this background, waste-derived fertilizers represent a promising circular economy
strategy, simultaneously addressing waste management, soil fertility, and climate mitigation. Recent
studies [1-3] highlighted the potential of fertilizers produced from organic residues to significantly reduce
greenhouse gas (GHG) emissions compared to conventional mineral fertilizers, increasing soil carbon
sequestration. Anaerobic digestates, composts, and vermicomposts are particularly relevant as sustainable
fertilizers. Over the past decade, anaerobic digestion has undergone substantial expansion on a global scale .
[4]
Within Europe, as of 2021, this development was reflected in the establishment of 1,023 industrial
biomethane production plants in addition to approximately 20,000 anaerobic digesters of varying
capacities . Beyond its technological diffusion, anaerobic digestion provides dual environmental and
[5]
agronomic functions: the generation of renewable biogas as an alternative to fossil-derived energy sources,
and the production of nutrient-enriched digestate that can be utilized as an organic soil amendment. A
recent study showed that nutrient-rich digestate can benefit plant growth by slowly releasing nutrients,
[6]
including nitrogen, phosphorus, and potassium. However, it should be used as fertilizer only after careful
testing of its chemical composition and potential contaminants, as well as after conducting growth
experiments. Composting stabilizes organic residues, reducing methane emissions otherwise associated with
landfill disposal, while vermicomposting produces amendments rich in bioavailable nutrients and beneficial
microbial communities . These technologies, when assessed through CFP analysis, reveal significant
[7]
mitigation potential when compared with synthetic fertilizers. For instance, a life-cycle perspective
demonstrated that compost derived from municipal solid wastes could replace up to 71% of synthetic
nitrogen, phosphorus, and potassium (NPK) fertilizers in urban and peri-urban agriculture, lowering
eutrophication potential and mitigating GHG emissions . Badewa et al. found that, compared with other
[7]
[8]
organic amendments (digestate and biosolids), compost had the greatest soil carbon sequestration potential.
Similarly, a recent review emphasized that organic fertilizers and biowaste-based amendments can serve as
key tools in Mediterranean agroecosystems to sustain soil fertility, enhance crop growth, control GHG
emissions, and increase soil carbon . Vermicomposting represents an environmentally sustainable
[9]
bioconversion process in which earthworms facilitate the degradation of organic residues, resulting in a
stabilized compost that is rich in nutrients and humic-like substances . The incorporation of vermicompost
[10]
into soil contributes to an increase in total soil carbon stocks by supplying organic matter and enhancing the
formation of stable soil aggregates. These aggregates play a critical role in physically protecting organic
carbon from microbial decomposition, thereby reducing carbon losses . The stability of soil organic carbon
[11]
(SOC) is further reinforced by the relatively high calcium content in vermicompost, which promotes
aggregation through cation bridging mechanisms. Carbon that becomes physically and chemically stabilized
within these aggregates exhibits lower turnover rates, resulting in greater long-term sequestration. Such
processes not only improve soil structure and fertility but also represent an important strategy for enhancing
soil health and mitigating atmospheric CO accumulation, with potential implications for climate change
2
adaptation and mitigation. The addition of different amendments to the soil plays a key role in driving soil
microbial diversity and, in particular, affects the fungi-to-bacteria ratio, thereby modulating soil carbon
dynamics by governing the balance between stabilization and mineralization, largely through mechanisms of