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.