Determination of Organic and Carbonate Carbon in Calcareous Soils Using Dry Combustion

A procedures is proposed which utilizes dry combustion and gravimetric determination of evolved CO 2 for the determination of both organic and carbonate C in soil samples. A series of experiments was designed to determine the optimum temperature and duration of combustion that would be consistent with efficiency of analysis. Heating at 575 °C for 900 s using an O 2 flow rate of 3.3 mL/s allows for determination of organic carbon (OC). Carbonate C from CaCO 3 and dolomite is then determined by subsequently heating the same sample at 1000 °C for 600 s using the same O 2 flow rate. This method gives quantitative recovery of organic and carbonate C from standard materials. Values for organic and carbonate C from 14 soil samples are in good agreement with existing procedures. The method is simple, requires a minimum of equipment, and has the benefit of using essentially the same procedure for both organic and carbonate C.