Gravimetric Determination of Soil Organic Matter

Studies were carried out to evaluate a gravimetric method for the determination of soil organic matter by the mass loss at 300C. The gravimetric method was compared with Walkley-Black, using several brazilian soils with variable chemical and physical properties. Gravimetric method was positively correlated with Walkley-Black method with the following linear regression equation: y = 3.72x + 0.29, r = 0.94. The angular coefficient 3.72 for tropical soils was greater than those reported in the literature for temperate soils (from 1.68 to 2.13). The difference was due to greater oxidation degree of the organic matter. When compared with Walkley-Black method, gravimetric technique showed certain distinct advantages such as no environmental contamination with Cr and improved laboratory safety eliminating the use of concentrated sulfuric acid.