Agriculture Reference
In-Depth Information
phases with low atomic number elements. In order to increase the emission of backscattered
electrons, the SEM microscope was generally operated with a beam current of 3 pA and an
accelerating voltage of 20 keV.
Statistical Analysis
ANOVA tests were performed on the samples data of trace and major element
concentrations and pH values obtained for the soil profile in all parcels. The data was
distributed in different levels of two categories; time (T0, T1, T2, and T3, corresponding to
parcels R, PG1, PG2, and PG3, PF1, PF2, PF3) and depth (horizons 0-5 cm, 5-10 cm, etc.).
When significant differences were found, a multiple comparison of mean values was carried
out by the Walker-Duncan test (P < 0.05). Normality of variances was examined by the
Shapiro-Wilk test, before running ANOVA. Correlation analysis (Pearson r) was carried out
between trace and major elements, TE concentrations and soil characteristics. All statistical
analyses were performed using SPSS Version 17.
R ESULTS AND D ISCUSSION
Soil Background Reference
The mineralogical results (XRD) showed that the background soil contained Quartz
(SiO 2 ), Calcite (CaCO 3 ), clay minerals (Montmorillonite, Kaolinite), Anatase (TiO 2 ) and
Hematite (Fe 2 O 3 ). The soil pH showed alkaline range (8.23 ± 0.12), and the cation exchange
capacity (CEC) exhibited relatively high values (31.06 ± 0.5 cmol kg -1 of dry weight) with a
dominance of calcium ions at the exchange sites.
The average background soil contained relatively low Cd concentration (0.30 ± 0.02 mg
kg -1 ) and high Zn concentration (103.35 ± 6.72 mg kg -1 ). As for Cu and Pb, their average
concentrations were found to be 35.84 ± 2.33 mg kg -1 and 11.50 ± 0.75 mg kg -1 , respectively.
No significant differences were found in TEs distribution with depth (till 55cm), except in
layer (30-55 cm) where Cu and Pb concentrations decreased with respect to upper layers.
It follows that, the study area presented elevated Zn total concentrations and slightly
elevated Cu concentration when compared to the world agriculture soils (20-30 mg kg -1 and
50 mg kg -1 for Cu and Zn, respectively) (Alloway 1995). Pb and Cd concentrations were
within the range of agricultural and normal soils (10-30 mg kg -1 and 0.2-1 mg kg -1 for Pb and
Cd; respectively) (Alloway 1995; Baize 1997). Moreover, the total Zn and Cu concentrations
exceeded the background values (12 ± 2 and 64 ± 2 mg kg -1 for Cu and Zn, respectively)
reported for the arable soils of North Lebanon (Nsouli et al. 2004). In general, the natural
occurrence and concentration of the studied elements were homogenous with depth.
However, Cu and Pb concentrations decreased in the deeper layer (30-55 cm). Chemical
speciation of the studied TEs in the reference soil showed they were mainly associated with
Fe and Mn oxides and hydroxides (reducible fraction F3) (64, 45, 43 and 13% for Cd, Pb, Zn
and Cu, respectively) and bound to the structure of clays (residual fraction F5) (63, 56, 23 and
11% for Cu, Zn, Pb and Cd, respectively). This partition of the studied elements is due to the
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