All air dried test media was oven dried for 8 hours at 110 °C
before samples were prepared. Polyvinyl chloride (PVC)
cylindrical columns (internal radius=10 cm, height=12 cm)
were used with markings at volumetric intervals of 50 cm3
from 950 cm3 to 1100 cm3. For each tested medium, starting
with dry media, an incremental amount of tap water was added
to and mixed with the dry media to produce tested media of
different water content levels. And then packed samples into
plastic bags out of bounds, and left for at least 24 h. The
samples were then re-mixed thoroughly, before being packed
carefully into cylindrical columns using the same degree of
tamping between each addition of material to marking column,
according to a predetermined bulk density, where the soil
is 1.18g/cm3, the peat 0.333/g/cm3, the perlite 0.16g/cm3
and the vinegar residue 0.136g/cm3. The probe sensitive side
closely placed above the samples, and tested on 3 different
directions (get the mean value of the three data). Note that
the samples of peat and vinegar residue were tamped to next
marking column in order to obtain another series points under
different bulk density. Despite that known amount of water
was applied, a gravimetric method, which is an only direct
reference method, was used to determine soil volumetric water
content. Assuming specific density of water to be 1 g/cm3,
soil volumetric water content was evaluated as a ratio of
mass of water (difference between mass of wet media