Agriculture Reference
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and P2 (particularly between January and April) caused TEs dilution, and thus a significant
decrease in Zn, Cu, and Pb average concentrations was observed in the soil profile, and this
trend persisted in the period between April and August, due to TEs uptake by growing plants.
However, Cd nearly constant average concentration in the soil profile between parcels P1 and
P2 indicated its accumulation in the soil matrix. In the period between September and
December (P2-P3), the drying-wetting cycle of the soil caused the re-augmentation of Zn and
Cu average concentrations in the soil profile. However, a different behavior was observed for
Pb and Cd that showed a slight decrease of their average concentration between P2 and P3
(13.06 and 12.70 mg kg -1 for Pb, 0.50 and 0.44 mg kg -1 for Cd in P2 and P3, respectively),
indicating possible uptake by plants or leaching toward the saturated zone.
Metals Mobility in Soil
In order to assess the chemical form of TEs and thus their mobility and potential risk on
the environment, speciation of Cu, Cd, Zn and Pb were performed in all parcels (R, PG1, PG2
PG3, PF1, PF2 and PF3). Five geochemical fractions were determined: the exchangeable
fraction (F1), the acid-soluble fraction (F2), the reducible fraction (F3), the oxidizable
fraction (F4) and the residual fraction (F5). The time-variations of concentrations of TEs in
the chemical fractions (F1, F2, F3, F4 & F5) at the different study depths (0-20 cm, 20-35 cm,
and 35-55 cm), were plotted on separate charts for each of the considered metals (Cu, Cd, Zn
& Pb) over the study period, as shown in Figure 5 and Figure 6. Different behaviors were
shown for the selected metals in the two applications as we explained below:
Figure 5. Time-variation of TEs geochemical fractions concentrations in the soil profile - Reference
parcel R (T=0); PG-amended parcels P1 (T1 = 5 months); P2 (T2 = 12 months); and P3 (T3 = 16
months). F1-Exchangeable; F2-Acid Soluble; F3-Reducible; F4-Oxidizable; and F5-Residual
fraction.
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