METHODS FOR DETERMINING ORGANIC-CARBON IN PODZOLIC SANDS

We compared three methods of estimating soil organic carbon (dichromate oxidation with and without external heating and loss-on-ignition) with a method for total carbon measured in an automated resistance furnace. In 38 surface (0–150 mm) podzolized sands the concentration of total carbon ranged from 0.39 to 4.57% and was highly correlated with all three methods (r2=0.99, p<0.0001, in each case). Dichromate oxidation with and without external heating recovered 99.1 and 88.8% of total carbon respectively, indicating that all carbon was organically bound, and that the ‘heat of reaction’ was not sufficient for total oxidation of organic carbon. Because the organic carbon content of the organic matter varied from 38% to 55% a mean value of 46% would be more appropriate for these soils than the Van Bemmelen factor of 58% for converting organic matter to organic carbon concentration The loss-on-ignition procedure represents a precise technique for the estimation of organic matter and, when calibrated, organic carbon in surface sandy soils. © 1990, Taylor & Francis Group, LLC. All rights reserved.