Carbon is present in soils in an organic and inorganic form. In calcareous
soilswith neutral to basic pH, inorganic C canmake up a significant
fraction of the total C, whereas in acidic soils it is absent. The chemical
quantification of total soil C is performed by dry combustion in an
Elemental Analyzer (EA), while inorganic C is commonly measured
by the pressure transducer method where the CO2 pressure builds up
after addition of HCl . Organic C can then be
obtained by difference. Also, organic C can be measured by EA, after
acid digestion of the samples (Harris et al., 2000), but a correction factor
may be needed at high concentrations of inorganic C . A few laboratories, where an EA is not available, use wet chemical
oxidation of organic C, referred to as the Walkley-Black method
to determine SOC. Conversion equations
for the harmonization of C data have been derived but need to be
used with caution because the readily oxidizable C measured by the
Walkley-Blackmethod is not necessarily correlated to themeasurement
by EA