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Page 6 of 19 Maffia et al. Carbon Footprints 2026, 5, 7

Box method , using tannic acid as standard. The concentration of water-soluble phenolic compounds was
[31]
expressed as tannic acid equivalents (μg TAE g D.W.). Cation exchange capacity (CEC) was analysed with
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barium chloride method . Cations and anions were detected using ion chromatography (Dionex ICS-1100,
[32]
Thermo Fisher Scientific, Sunnyvale, CA, USA) .
[29]
Soil biological analysis
Microbial biomass carbon (MBC) was assessed with the chloroform fumigation-extraction procedure on
[33]
fresh soil. Fumigated and unfumigated soil sample extracts were used to detect soluble organic carbon .
[28]
Fluorescein diacetate hydrolase (FDA) activity was determined according to the method of Adam and
Duncan . Dehydrogenase (DHA) activity was assessed with the method used by Von Mersi and Schinner .
[35]
[34]
The decrease in the absorbance was measured at 240 nm, using the extinction coefficient of 39.4 M cm .
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Protease activity was detected as reported in Muscolo et al. . Urease activity was determined as described by
[15]
Kandeler and Gerber . Ammonium concentrations were determined at 690 nm by using a calibration curve.
[36]
The results are reported as μg N-NH g d 3 h .
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4
Percentage CFU (%) = (CFU of the group / Total CFU) × 100 (3)
[15]
where:
• CFU of the group = colony-forming units of fungi, bacteria, or actinomycetes;

• Total CFU = sum of CFU of all groups.

The biomass of each group is calculated using :
[15]

μg C g = fraction of each group × total MBC (4)
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where:

• Fraction of the group = CFU of the group / Total CFU;

• MBC = microbial biomass carbon (µg C g ).
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Environmental impacts based on life cycle assessment
The environmental impacts of fertilizers were evaluated using the Life Cycle Assessment (LCA) approach,
following the ISO 14040:2006 (Environmental management - Life cycle assessment - Principles and
framework) and ISO 14044:2006 (Environmental management - Life cycle assessment - Requirements and
guidelines) standards [37,38] . The methodological framework was applied in accordance with ISO 14025:2006
(Environmental labels and declarations - Type III environmental declarations - Principles and procedures)
and the Product Category Rules (PCRs). Since no specific PCRs currently exist for organic fertilizers derived
from organic matrices, PCR 2010:20 (EPD, 2010) , which refers to fertilizer production, was adopted, as
[39]
suggested by Egas et al. .
[40]

According to ISO 14040:2006 , an LCA consists of four phases:
[37]

I. Goal and Scope Definition: The aim of this study was to assess the contribution of different fertilizers to
climate change by quantifying their Global Warming Potential (GWP, 100 years), expressed as kg CO eq per
2