Agriculture Reference
In-Depth Information
I NTRODUCTION
Large application of phosphate fertilizers and by-products has been practiced on arable
lands, to improve crop production, induced soil nutrients deficiency, and increasing the levels
of available S and P. However, contamination of agricultural soils with trace elements (TEs)
such as Cd, Pb, Zn and Cu, and with fluorine can occur as these elements are transferred
during manufacturing from phosphate rock to phosphate fertilizers (PFs) and by products
such as phosphogypsum (PG) which is a di-hydrate calcium sulfate. Concentrations of Cd,
Pb, Zn and Cu can vary in PFs and PG depending on the origin of phosphate rock and the
process used.
Many studies have been conducted on assessing the use of PFs and PG as amendment on
agricultural soil (Adriano 1986; Arocena et al. 1995; Conkline 1992; Guttormsen et al. 1995;
Jeng and Singh 1995; Lambert et al. 2007; Loganathan et al. 1995; Malavolta 1994;
McLaughlin et al. 1996; Morvedt 2005). Cd has been the most concerned element in PFs
application since it can accumulate in relatively high amounts in soil and plants which could
be harmful to human health (Kirkham 2006). Al-Masri et al. (2004) indicated that Cu, Zn and
Cd could be transferred from PG into water and subsequently to the soil horizons, which
should be considered when PG is used as amendment to agricultural soils. Furthermore, in
studying the cumulative effect of the amendment of PG on the uptake of elements by
tomatoes, Abril et al. (2008) showed a possible direct effect of PG amendment in increasing
Cd levels in tomato crops, which was less than the permissible limit (50 ppb). On the other
hand, earlier studies showed that PFs application in recommended rated on Brazilian soils did
not increase TEs concentration to hazardous levels in short and medium terms (De Conceicao
and Bonotto 2006; Malavolta 1994). Depending on their different forms and phases in soil or
mobility, TEs can be accumulated in plants, migrated into groundwater, or associated with
different soil components (e.g., organic matter, clays, Fe and Mn oxides, carbonate minerals).
Determination of different forms or phases of a TE, referred to as speciation, is primordial to
assess its mobility and thus the potential risk of its bioavailability. Soil properties such as pH
play a key role in releasing or holding a TE in a defined phase (Kabala and Singh 2001).
A recent study on the effect of phosphate industry emissions on soil contamination
showed that PG had the highest contribution in TEs input into the surface soil (Kassir et al.
2012b). Results suggested that soil contamination with TEs carried with PG and phosphate
particulates could be potentially hazardous to plants and groundwater. Nevertheless, further
investigations on the behavior, forms and dynamics of these TEs in the soil had been
recommended to better assess the risk factor.
It follows that our study has been focusing on the time variation aspect of TEs mobility
following PFs and PG application on soil and their transfer factor to plants.
M ETHODS
Experimental Study Area
For this purpose, an experimental field has been realized in an area located off the
Mediterranean east cost in north Lebanon, and extends over 100 km 2 of agricultural lands
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