PCA is a way to identify the controlling processes in a complex data
set and state the data so as to highlight the similarities and differences
[21]. PCA was performed with the concentrations of Cd, Pb, Cu, and Zn
in leachates after SAR leaching in order to establish the basic clustering
patterns of nine soils. Two principal components were extracted,
explaining 89.5% of the total variation in original variables (Fig. 4). The
line with a closed circle in red provides extra information at a glance
on the heavy metal characterization of leachates from each soil
treatment