Soil carbon determination by high temperature combustion a comparison withdichromate oxidation procedures and the influence of charcoal and carbonate carbon on the measured value
Gl. Kerven et al., Soil carbon determination by high temperature combustion a comparison withdichromate oxidation procedures and the influence of charcoal and carbonate carbon on the measured value, COMM SOIL S, 31(11-14), 2000, pp. 1935-1939
The measurement of organic carbon in soils has traditionally used dichromat
e oxidation procedures including the Wakley and Black and the Heanes method
s. The measurement of carbon in soils by high temperature combustion is now
widely used providing a rapid automated procedure without the use of toxic
chemicals. This procedure however measures total carbon thus requiring som
e means of correction for soil samples containing carbonate and charcoal fo
rms of carbon. This paper examines the effects of known additions of charco
al to a range of soil types on the results obtained by the Walkley and Blac
k, Heanes and combustion methods. The results show, that while the charcoal
carbon does not react under Walkley and Black conditions, some proportion
does so with the Heanes method. A comparison of six Australian Soil and Pla
nt Analysis Council reference soil samples by the three methods showed good
agreement between the Heanes method, the combustion method and only slight
ly lower recoveries by the Walkley and Black procedure. Carbonate carbon wi
ll cause an overestimation of soil organic carbon by the combustion method
thus requiring a separate determination of carbonate carbon to be applied a
s a correction. This work shows that a suitable acid pre-treatment of alkal
ine soils in the sample boats followed by a drying step eliminates the carb
onate carbon prior to combustion and the need for an additional measurement
. The measurement of carbon in soils by high temperature combustion in an o
xygen atmosphere has been shown to be a rapid and reliable method capable o
f producing results in good agreement with one of the established dichromat
e oxidation procedures.