Humus Determination.—For some time quantitative determinations of humus have been carried out, humus being understood to consist of organic matter in the process of decomposition. Scil samples from different root layers should always be examined separately. The simplest process for determination of humus is that used for soils with no lime and little clay. About 3 to 10 g. of air-dried soil are heated to white heat in a platinum crucible for 30 to 60 min., and the amount of loss determined. At the same time a sample is dried for 3 hr. at 110°C. The resulting loss of water is calculated for the ignited soil and deducted from the loss due to ignition. (Braun-Blanquet 1932:252)
BRAUN-BLANQUET, Josias. 1932. Plant sociology: the study of plant communities. (Trans.: George D. Fuller; Henry S. Conard) New York: McGraw-Hill Book Company.