3.4 Selecting soil quality indicators
To evaluate the sensitivity of different soil chemical and physical
quality indicators, we performed a principal component analysis. The
first three principal components were selected because they accounted
for approximately 50% of the total variation. Though the contribution
of the three PC to the explanation of the total variation is relatively
small, it still displays loadings above 0.4 with at least three soil
properties (S. Material 3). CEC, total carbon, total Phosphorus, and
Inorganic Phosphorus contributed more strongly to the variability of
PC1. PC2 is positive related to available ammonium, available Olsen-P
and Porosity, and negative related to nitrate. PC3, which explains the
11% of the total variation, have large negative loadings for the
infiltration rate and K-RUSLE and positive with porosity.
The k-means clustering algorithm display that the CG site tends to
differ from the OG sites even though both PC’s only accounts for
approximately 40% of the total variation (Figure 4). The chemical
properties allow a fair clustering of the sites where loadings of total
and inorganic Phosphorus, CEC, and Kjeldahl Nitrogen contribute the
most. All the differences described above and shown in Figure 5.