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Figure 7. Transfer factor of TEs in the plants - Reference parcel R (T=0); PF-amended parcels P1 (T1 =
4 months); P2 (T2 = 11 months); and P3 (T3 = 15 months).
The copper TF went through an increase in P1 by about 44% relative to the reference,
declined to the reference value in P2, then increased again by about 71% in P3 (Figure 7). If
we examine Figure 6 for Cu fractions in layer 0-20 cm, we find a similar fluctuating pattern in
the mobile fractions (F1 & F2) concentrations, with the pH factor favoring the availability of
the carbonate fraction (F2) to plant uptake.
Similarly, the Pb TF went through an increase of nearly 52% from R to P1, a drop in P2,
followed by an increase of about 86% in P3 (Figure 7). However, this increase in
bioavailability of Pb in P3 is contradicted with the prevailing insoluble and residual Pb
fractions in layer 0-20 cm (Figure 6). This could be explained by the idea that some plant
roots were extended to deeper layer (20-35 cm), where the Pb plant available fraction F2
prevailed in P3 (Figure 6).
As for Zn, plant available fractions (F1 & F2) barely existed in parcels R, P1 and P2, with
bio-available fraction F1 appearing in parcel P3 with a concentration of about 20 mg kg
-1
in
layer 0-20 cm (Figure 6). Zn plant availability, however, remained the same in P3 as in the
other parcels, with relatively low TF (0.11 ± 0.01) (Figure 7). This could possibly be due to
the existence of competing available Cu (László Simon 2000; Tani and Barrington 2005) in
P3 layer 0-20 cm (Figure 6).
There was little evidence of significant elevated uptake of TEs in soil extensively
amended with PFs. Pb, Zn, Cu and Cd concentrations were within the normal levels reported
by Chaney (1989) (2-5 mg kg
-1
for Pb; 15-150 mg kg
-1
for Zn; 3-20 mg kg
-1
for Cu; 0.5-1 mg
kg
-1
for Cd) though they are considerably higher than the reference, particularly for Cd. This
phenomenon could be attributed to the formation of TEs phosphate compounds which are
non-absorbable. In fact, it is recognized that high levels of phosphate fertilization decrease Zn
concentrations in plant tissues (Lindsay 1972; Loneragan and Webb 1993; Moraghan 1984),
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