2.2.1 Determination of soil physical characteristics
The SWRC was measured for matric potentials of -1, -2, -4, -6, -8 and
-10 kPa using Buchner funnels (Haines, 1930) and for matrix potentials
of -33, -66, -300 and -1,500 kPa using a Richards pressure plate
extractor (Klute, 1986). The samples were allowed to reach the
equilibrium moisture content at each potential, weighed and subjected to
the next potential as per drainage procedure. After exposure to a
tension of 1500 kPa, the samples were re-saturated and equilibrated at a
tension of 6 kPa for determination of the PR. The samples were then
dried in an oven at 105 ± 2 ºC for 24 hours to determine the water
content (θ) and BD.
The soil penetration resistance (PR) was determined using an electronic
bench penetrometer equipped with a straight circular cone tip of 45° and
a diameter of 4 mm at a constant velocity of 2 mm s-1for the entire length of the sample (50 mm) (Tormena et al., 1998).
After disregarding the first and the last 25 readings, an average PR
value for each sample was calculated (Serafim et al., 2013). The
clay-sand contents and PD were measured according to Teixeira et al.
(2017). For the granulometric analysis, the soil was physically
dispersed in a Wagner-type rotary agitator with slow agitation.