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Page 8 of 19 Maffia et al. Carbon Footprints 2026, 5, 7

Table 1. Chemical and humic properties of compost (C), vermicompost (V), digestate (D), and sulfur bentonite with olive pomace
(SBO)

C V D SBO
TOC 44 ± 1.4 53 ± 2.4 45 ± 1.5 6.3 ± 0.5
a
c
b
b
TEC 17 ± 1 24 ± 1.1 18 ± 1 1.8 ± 0.5
b
c
a
b
HA + FA 14 ± 1 14 ± 1.2 11 ± 1 nd
a
b
a
HA 9 ± 0.5 8 ± 0.9 3 ± 1 nd
b
a
a
FA 5 ± 0.3 6 ± 1.0 8 ± 0.2 nd
a
b
b
c
a
b
HA/FA 1.8 ± 0.4 1.3 ± 0.4 0.35 ± 0.2 nd
HR 30 ± 1.8 28 ± 1 24 ± 1.4 nd
b
a
a
HD 81 ± 1.9 65 ± 2.5 61 ± 1.9 nd
b
a
b
HI 0.37 ± 0.01 0.22 ± 0.04 0.63 ± 0.06 nd
b
a
c
E4/E6 3.3 ± 0.9 4 ± 0.8 9.1 ± 1.0 nd
a
b
b
WSP 2.3 ± 0.06 2.1 ± 0.03 5 ± 1 nd
b
a
b
Total Organic Carbon (TOC, %), Total extractable Carbon (TEC, %); Humic acid carbon (HA%); fulvic acid carbon (FA%); humic acid carbon (HA,
%) + fulvic acid carbon (FA, %), humification rate (HR %), humification degree (HD, %), humification index (HI, %), E4/E6 (ratio of the
absorbances at 465 and 665 nm), Water soluble Phenols (WSP, mg TAE g d.w). Different superscript letters within the same row indicate
-1
significant differences among treatments according to Tukey’s Honestly Significant Difference (HSD) test (P < 0.05).
Table 2. Chemical properties of soil at the beginning of the experiment (CTR0), untreated soil (CTR), and soil treated with compost
(C), vermicompost (V), digestate (D), and sulfur bentonite with olive pomace (SBO)
CTR0 CTR C V D SBO
pH (H 2 O) 8.3 ± 0.55 8.2 ± 0.52 7.6 ± 0.80 7.6 ± 0.40 7.2 ± 0.40 5.2 ± 0.40
b
c
d
b
a
a
EC (dS/m) 310 ± 10 350 ± 12 433 ± 9 375 ± 12 421 ± 12 120 ± 11
a
c
b
a
e
d
a
a
WC (%) 21 ± 2.6 22 ± 2.1 27 ± 1.7 28 ± 1.70 24 ± 1.70 25 ± 1.70
a
b
a
b
WSP (µg TAE g d.s) 16 ± 2.0 18 ± 2.8 44 ± 2.7 40 ± 3.3 41 ± 3.2 28.8 ± 2.8
c
a
-1
a
b
a
c
TOC (%) 1.0 ± 0.16 0.9 ± 0.16 1.7 ± 0.15 2.1 ± 0.25 1.3 ± 0.25 1.54 ± 0.19
b
b
b
a
c
bc
TN (%) 0.13 ± 0.01 0.14 ± 0.01 0.30 ± 0.02 0.22 ± 0.04 0.21 ± 0.03 0.14 ± 0.02
b
a
b
c
c
c
C/N 7.6 ± 0.35 6.4 ± 0.4 5.7 ± 1 9.5 ± 0.6 6.2 ± 0.5 11 ± 0.9
b
ab
a
b
c
a
SOM (%) 1.72 ± 0.3 1.55 ± 0.27 2.92 ± 0.25 3.6 ± 0.13 2.24 ± 0.13 2.64 ± 0.23
b
ab
c
b
c
cb
HC (%) 0.50 ± 0.06 0.55 ± 0.03 0.63 ± 0.02 0.70 ± 0.01 0.60 ± 0.01 0.62 ± 0.01
a
b
b
b
b
b
FC (%) 0.40 ± 0.06 0.39 ± 0.08 0.26 ± 0.05 0.38 ± 0.03 0.55 ± 0.03 0.59 ± 0.02
c
d
a
a
c
b
HC/FC 1.25 ± 0.05 1.41 ± 0.09 2.42 ± 0.8 1.84 ± 0.9 1.09 ± 0.04 1.05 ± 0.04
d
b
a
a
c
d
c
c
e
d
MBC 899 ± 5 789 ± 7 1,087 ± 12 999 ± 11 957 ± 13 932 ± 14
a
b
CEC [cmol(+) Kg ] 18.9 ± 1 18.7 ± 0.9 22 ± 1.1 23 ± 1.2 22 ± 1 19.9 ± 0.9
-1
b
a
a
b
a
b
Control 0 (CTR0) is the soil before the start of the experiment. pH; OC: organic carbon (%); OM: organic matter (%); C/N: carbon-nitrogen ratio;
CEC: cation exchange capacity (meq/100 g); Tot N: total nitrogen (%); EC: electrical conductivity (dS/m); WC: water content (%); TOC: total
organic carbon; TN:total nitrogen; C/N: carbon to nitrogen ratio, dimensionless; SOM: soil organic matter; HC:Humified Carbon; FC: fraction of
carbon; MBC: microbial biomass carbon. Data are the means of three replicates ± standard deviation. Data are the means of three replicates ±
standard deviation. Different superscript letters within the same row indicate significant differences among treatments according to Tukey’s
Honestly Significant Difference (HSD) test (P < 0.05).
Soluble Phenols, Total Organic Carbon , and Total Nitrogen also increased compared to CTR0 and CTR.
Soil analysis further revealed significant differences among treatments [Table 2]. Soil texture remained
unchanged (data not shown); however, pH decreased under all treatments compared to CTR0 and CTR, with
the most pronounced reduction observed for SBO.