A RAPID MICROWAVE DIGESTION METHOD FOR COLORIMETRIC MEASUREMENT OF SOIL ORGANIC-CARBON

Soil organic matter is an active component of agroecosystems. Rapid an d precise measurement of organic carbon (C-org) is essential to monito r changes in organic matter and soil quality. A new semi-micro wet dig estion method for the determination of Corg Was developed using rapid microwave energy applied at 500 J mL(-1) digestion mixture to enhance oxidation of C-org by K2Cr2O7 and cone. H2SO4. This proposed method an d three existing methods of soil C determination were compared with th e LECO dry combustion carbon analyzer. The r(2) value for the proposed microwave method regressed against LECO C was 0.9913. The recovery of C-org by the rapid microwave digestion method for spectrophotometric measurement was 91.7+/-1.2% (conversion factor 1.09) of C measured by the LECO dry combustion method. Compared to the traditional Walkley-Bl ack's method, the proposed spectrophotometric with microwave digestion method was rapid and more precise, used smaller reagent volumes, and produced less waste.