3.3. Evaluation of the Soil Quality Index (SQI)
The eigenvalues of the first four components were all ≥ 1 and explained
84.87% of the total variance (Table 3). In the first component (PC-1),
the indicators with the highest weight were aeration porosity (AP),
saturated hydraulic conductivity (Ksat), zinc content
(Zn) and exchangeable acidity (EA). AP and Ksat showed a
high correlation (r>0.80) (Table 4), therefore, due to the
higher load and ease of measurement, AP was selected as an indicator in
PC-1. In the second main component (PC-2), TOC and pH had the highest
loads and showed a high degree of significant association (P≤0.01), with
r = -0.79 (Table 4), thus, TOC was selected in PC-2. In the third main
component (PC-3), total porosity (TP) and soil bulk density (BD) had the
highest loads and also showed a significant correlation, with r = -0.63
(p<0.05). However, since total porosity did not show
significant differences in Tukey’s mean comparison test and considering
that bulk density is an integrative variable and influences different
important functions that define soil quality, it was selected
(Blanco-Canqui & Ruis, 2018). Finally, in
PC-4, leaf litter (LL) production was selected because it showed the
highest load.
Table 3.
Table 4.
Based on this, the minimum data set selected to calculate SQI were Zn,
AP, TOC, BD and Leaf litter. With the value of the weights or loads
based on the PCA (Table 5), the SQI was determined using the following
equation Eq (3):