2. Materials and methods
2.1. Experimental design
The experimental site was located in an agricultural area, where broccoli, lettuce, cotton and artichoke are mainly produced, near San Ginés de la Jara (Murcia) (longitude W00°50′50″, latitude N37°38′45″), 3.2 km from the Mar Menor sea and 2 km north from the closest old mining site. The soil was a calcareous clay loam with 39.2% clay, 27.4% silt and 33.4% sand, classified as Xeric Torriorthent (Natural Resources Conservation Service, 1999). Some properties of the soil are shown in Table 1. The concentrations of Zn and Pb in this soil greatly exceed the limits established by the EU for agricultural soils (Council of the European Communities, 1986). The different particle size fractions of the soil were isolated and their mineral composition was determined by X-ray diffraction (data not shown). The clay fraction (