Agriculture Reference
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background range. The time-variation of Cu concentrations over the studied depths exhibited
generally a steady function increasing at slight rate with time.
Following PG amendment, a general increase of TEs concentration could be observed.
During rainy period (October - April), Cd concentration decreased (0.5 to 0.35 mg kg
-1
)
(Figure 3), whereas Zn, Pb and Cu concentrations were generally increasing at almost all
depths (110.61 to 115.76, 12.88 to 15.49, and 38.31 to 39.90 mg kg
-1
respectively). However,
in the deeper layers (35-55 cm), Pb and Cu concentrations decreased (P< 0.01) while Zn
concentration showed no significant difference between parcels in this particular layer. Cd
concentration displayed a significant difference (P < 0.05) between parcels (R, PG1, PG2 and
PG3) only in the upper layers (0-20 cm). A general remarkable decrease in TEs
concentrations was observed over the study period in the layer (10-20 cm) particularly over
the spring-summer period. On the other hand concerning PF application, to simplify the
tracking of the profiles variations, the eight layers in each parcel were grouped in three depth
zones: upper (0-20 cm), intermediate (20-35 cm), and lower zone (35-55 cm); zone TE
concentration was taken as the average content of TE in the zone layers. Generally, a similar
trend was observed for
the studied TEs. For the overall profile, peak concentrations of TEs
(Cu: 43.13, Cd: 0.52, Zn: 116.36, and Pb: 14.92 mg kg
-1
) occurred four months after
amendment (in January, parcel P1). Then, TEs average total concentration decreased between
parcels P1 and P2 (February-August) to finally reach near background values in parcel P3
(December) (Figure 4). However, Cd average concentration remained relatively constant
between parcels P1- P3 (0.44 to 0.52 mg kg
-1
). Changes in Cd concentration between parcels
occurred only in the upper layers (0-20 cm) (0.31 to 0.71 mg kg
-1
), thus not reaching deeper
layers, indicating possible in situ release and recovery. A soil enrichment of about 0.30 mg
kg
-1
(~100% enrichment) in Cd remained in P3 (11 months after PF application) in the upper
zone (0-20 cm). Layer 35-55 cm showed an increase in Pb content between P1 and P2
(February-August). Practically, with the exception of Cd, slight variations in TE total
concentrations occurred between P2 and P3 (August-December), where the TEs content in the
soil approached the background levels, indicating the direct effect of PF on the soil profile
took place mainly during around a year following PF application. No evidence of released
TEs accumulation in the soil was observed by the end of the sampling period (15 months after
PF application)-Except for Cd which was somewhat accumulated in the upper layers (0-20
cm). However, Cd content in this layer was decreasing between P2 and P3, and by
extrapolation, it would eventually reach the background level.
A decrease of soil pH following the PF amendment was detected from the surface (0-5
cm) till layer 15-20 cm that showed the lowest value with slightly acidic pH (6.6 ± 0.2) in
parcels P1 and P2. Statistically, the fluctuation of TEs concentration in all depths with time
proved a significant difference in the average concentration between parcels for Cu, Zn and
Pb. The upper layers of the parcels (down to 25 cm) showed a significant difference with time
for Cd.
As a result of local and temporary pH decrease after PFs amendment, and heavy rainfall
during October-January, TEs average concentrations increased in the soil profile to reach
their highest values in parcel P1 (Figure 4). However, despite the relatively massive quantity
of PFs amendment, their concentration remained below the permissible limits of TEs in
agricultural soils (Cu: 63, Cd: 1.4, Zn: 200, and Pb: 70 mg kg
-1
) (CCME 1999). TEs were
transferred from PF and moved downward through the soil profile with incoming rain water
creating temporary leaching conditions. Generally, the continuous rainfall between parcels P1
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