A Modified Procedure for Determination of Carbonate Carbon and its Application for Estimation of the Reactivity of Calcitic Limestone in Field Soils

Abstract

A modified procedure for determination of carbonate carbon and its application for estimation of the reactivity of calcitic limestone in field soils. Received hlay 15, 1985. Acta Agric. Scand. 36:71-80. 1986.A simple method of determining inorganic carbon, especially adapted to low-carbonate soils, is described. It consists in the digestion of the sample, containing between 0.5 and I20 mg carbonate-C, in approximately 1 hl HCI at room temperature. The C 0 2 evolved during a 2-h treatment on a rotary shaker Nas absorbed in a KOII trap. After addition of BaCI,, the COz \$as quantified by a two-end-point acidimetric titration. In samples containing dolomite, the digestion period had to be prolonged to 4 h. Owing to relatively slight interference by decarboxylation, the detection limit (=twice the background level) for carbonate-C in the topsoil layer of cultivated soils (~4 % Ohi) and of the forest floor ( 4 0 ton ha-') \\as estimated at 400 and 20 kg CaCO,, respectively. The above method was applied to the estimation of the dissolution rate of a Cretaceous limestone, when applied on the surface of forest soil. From data on residual carbonate in the soil profile registered after an observation period of 16 months, it xas concluded that, with a limestone-application rate of 3 200 kg CaCO, ha-', the proportion of the limestone dissolved varied between 13 and 59%, depending on the particle size fraction of the limestone used. The lower figure refers to a particle-size fraction of 1.0-3.0 mm, and the higher to a fraction <O. I5 mm (dia.).