Semi-detailed Soil Survey of the LIuidas Vale Area, St. Catherine-St ...

MATERIALS AND METHODS
Bulk density: Bulk density is determined by drying a known volume (100 cc)
of undisturbed soil at 105°C, after which the oven-dry weight of the
soil is divided by the volume of the soil.
Calcium carbonate: (according to Van Wesemael; only in samples with
pH(H20) > 6.5). Gravimetric determination of the loss of weight, after
treatment with 4N HC104.
CEC(-NH40Ac): For the cation exchange capacity, the sample is leached
subsequently with 1 M ammonium acetate at pH 7.0. 80% ethanol to
wash out the excess of ammonium and 10% KG at pH 2.5 to replace
the absorbed ammonium. In the leachate, ammonium is determined
by distillation and titration.
EC (1:2.5): The electrical conductivity is measured in a 1:2.5 soil-water
extract.
Exchangeable acidity/aluminium: (only in samples with pH < 5.5). The soil is
leached with 1 M KC1. Exchangeable acidity (Al + H) and aluminium are
determined titrimetrically.
Exchangeable bases: Exchangeable Na and K are determined flamephotometrically
in the leachate of the CEC-determination.
Exchangeable Ca and Mg are determined in the same leachate using an
atomic absorption spectro-photometer.
Organic carbon: (according to Walkley and Black). Organic matter is oxidized
with an excess of potassium dichromate in an acid medium. The excess
is back-titrated with ferrous ammonium sulphate.
Particle size analysis: (pipette method). The sample is pre-treated with H2O2
and sodium acetate, in order to remove organic matter and CaC03.
After dispersing with Na-hexametaphosphate, the clay and silt
fractions are calculated for samples, taken from the suspension with a
pipette. The total sand fraction is determined by wet sieving; the
different sand fractions are determined after dry sieving.
pH (H2O): Potentiometric determination in a 1:2.5 soil-water suspension.
pH (KG): Potentiometric determination in a 1:2.5 soil-1 M KG suspension.
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