2.4 Statistical analysis.
For each chemical and physical parameter, comparisons between treatments
were carried out using a two-way ANOVA following the general linear
model of the ”CAR” R package (Fox et al., 2012), followed by posthoc
multiple comparisons (LSD test). All the data was checked to meet the
assumptions of normality of residuals and homoscedasticity and
transformed when needed. For P Olsen, we used a Negative Binomial Hurdle
model approximation because of the amounts of zeros (concentrations
below the detection limit). Soil data were subjected to a principal
component analysis (PCA) for data ordination and reduction and
distinguished if conditions were different, and determined what groups
of soil indicators were more effective on differentiating grazing
intensity. The data was auto-scaled previous to the PCA because of the
different natural scales between variables and to attribute an equal
weight to each variable (Sena et al.,2002). All statistical analysis was
conducted in R (R Core Team, 2013).
3. RESULTS