*2.4. Soil Sample Analysis*

Soil samples were dried at room temperature and then sieved using a vertical sieving machine to separate and sort grain-size fractions. The pH was measured following METHOD 9045D. Loss on ignition (LOI) analysis was used to determine the organic matter content (%OM) of the three soil samples. The colorimetric molybdenum blue method

was used to determine the available phosphorus in soil samples as orthophosphate after digestion by HNO3-HCL 1:3 (*v*/*v*). The cation exchange capacity (CEC) is related to the soil's clay and organic matter content. This measurement makes it possible to know the total quantity of exchangeable cations (K<sup>+</sup> , Ca2+, Mg2+, Na<sup>+</sup> , H<sup>+</sup> , etc.) tending to retain the nutrients and phytosanitary products available to plants. The CEC of the soils was determined using the Metson method [41], which is based on the extraction of cations by 1N ammonium acetate at pH 7.0.

Major elements such as Ca, Fe, K, Mg, and Na, and heavy metals such as, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Se, Ti, and Zn were determined in the fine fraction of the soil (<63 µm fraction) using inductively coupled plasma–optical emission spectroscopy (ICP-OES, Agilent 5100, Tokyo, Japan). Analysis was performed after acid digestion (HNO3-HCL 1:3 (*v*/*v*)) using a DigiPREP blocks digestion and heating system (SCP Science, Montreal, QC, Canada). The concentrations of heavy metals were expressed on a dry mass basis (mg/kg). Given that the sampled soils were characterized by a coarse texture mainly dominated by sand particles, trace elements and macronutrients were analyzed on the fraction below 63 µm. From another point of view, the objective of analyzing the fine fraction of the soil despite its low percentage is to give an idea about the role of the silty and clayey fraction in the retention of heavy metals in sandy soils.
