A method of and apparatus (41) for determining the organic carbon content of soil in heated air or gas is forced through a soil sample (36) to burn off or oxidize organic carbon in the sample with the change of weight of the sample (36) indicating the carbon content in the soil sample (36) and thus the soil from which the sample (36) is taken. The apparatus (41) includes a housing (47) in which one or more soil samples (36) may be located, a heater unit (51) for heating the air or gas for passage through the soil samples (36) to burn off organic materials therein including organic carbon. The apparatus (41) also includes a weighing device (76) which enables the change of weight of the soil samples (36) to be determined while the samples (36) remain within the housing (47).