2.4. Statistical analysis
The data obtained were analysed to check its normal distribution using the Kolmogorov-Smirnov test, and the homogeneity of variance was also analysed using the Levene test. After fulfilling both assumptions, the data were analyzed using the parametric mean comparison test (ANOVA), considering the study periods (years) and the types of amendments (Org., Cal. and Arc.) as independent variables. Subsequently, the Tukey post hoc test determined the significant differences (p<0.05) between the different independent variables considered. All statistical analyzes were carried out using SPSS software v.20.0 (SPSS Inc., USA).
To show the mean values of the concentrations of soluble and bioavailable contaminants in the different sampling periods, radial charts were constructed with Excel, the scale was determined independently for each item. The area obtained for each element was measured with Adobe Acrobat 9.0 (Adobe Systems Incorporated, USA) and the sum of the areas obtained for each treatment and each year was calculated. Finally, the soil remediation index (RA) was calculated according to Xiong et al. (2015), who define this index as the relationship between the surface of each polygon in each sampling period and the surface of the initial polygon (1998), therefore considering RA equal to 1 for the year 1998.