2.4 Soil sampling and analysis
A soil profile was opened, described, and classified in each vegetation plot according to the World Reference Base for soil resources (FAO, 2015). We collected deformed composed samples in the superficial horizons (A Horizon) in each profile, which varied from two to 10 cm in depth. We only considered this horizon because it exerts a more significant influence on the regenerating stratum since the roots of the seedlings do not yet reach the deepest horizons (Taiz et al., 2017). The collection method was based on the Field Soil Description and Collection Manual (Santos et al., 2005). We used a properly sanitized garden shovel, avoiding contamination risk of the samples, and collecting approximately 2 kg of soil in plastic bags.
These samples were air-dried, ground, and sieved in a 2 mm sieve prior to analysis. The coarse sand, fine sand, silt, and clay contents were determined after slow agitation with 0.1 M NaOH by the sieve-pipette method (Donagema et al., 2011). The soil pH was determined in deionized water (1: 2.5). The Al3+, Ca2+, and Mg2+ contents were determined by 1 M KCl extraction. K+, Na+ and P were determined after Mehlich-1 extraction. Potential acidity (H+Al) was determined by calcium acetate at pH 7.0. The soil organic carbon content was determined by acid digestion, according to the Walkey-Black method (Silva and Mendonça, 2007). The total nitrogen content was determined by the Kjeldahl method. the sum of bases (SB), cation exchange capacity (CEC), base saturation (V), and C/N ratio were subsequently calculated from these procedures.
Undisturbed samples were collected using volumetric rings (Donagema et al., 2011). The bulk density, particle density and the soil water retention curve (0, -6, -10, -30, -100, -1500 kPa) were determined. Total porosity, field capacity (FC), wilting point (WP), water subject to drainage, available water, and unavailable water were calculated from these data.