Organic Carbon

Carbon (C) is the chief element of soil organic matter that is readily measured quantitatively. Values for the organic-C content of soils may be expressed as such or may be reported as total organic matter by multiplying the figure for organic-C by the conventional "Van Bemmelen factor" of 1.724. Methods for the determination of total-C in soils by wet- or dry-combustion are basic for all quantitative estimates of organic-C. With noncalcareous and unlimed soils, total-C is considered to be organic-C. With calcareous soils, carbonate must be removed before analysis for total-C, or the total-C must be corrected by subtracting carbonate C determined on a separate sample. With calcareous soils, the choice between determining organic-C on the sample after removal of carbonate-C, or computing organic-C by subtracting carbonate-C from total-C depends on the need for quantitative data on carbonate-C.