DETERMINATION OF ORGANIC CARBON IN SOIL AND PLANT MATERIAL

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Abstract
Summary: A wet‐oxidation technique for determining organic carbon in soil, plant material, and aqueous plant extracts is described. The oxidation is carried out by heating the soil or plant sample (containing 50–100 mg. carbon) with a mixture of potassium dichromate, sulphuric, and phosphoric acids for 10–15 min., and the carbon dioxide liberated is determined gravimetrically after absorption in soda‐lime. With slight modifications, the method has proved useful for the determination of carbon in plant extracts and would also appear suitable for a soil extract. A method is described for the removal of carbonates without loss of organic carbon. It is shown that heating a wet soil at 105° C. causes considerable loss of organic carbon. Inert carbonaceous material, such as coal or charcoal, is oxidized by this wet‐digestion method, thus producing erroneously high results for the carbon content of soil organic matter.The method is at least as accurate as the conventional dry‐ combustion technique, and is less time‐consuming, only one hour being required for a determination. The apparatus is of simple design and with the exception of the needle valve can be readily constructed from normal laboratory glassware. The method can deal with fairly large samples of materials, thus preserving an essential feature of established macro‐methods.This technique of determining carbon is convenient for the fairly rapid analysis of soils and plant materials where an accurate total‐carbon value is required.