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.