Anderson, D. W., authorPaul, E. A., authorSt. Arnaud, R. J., authorAgricultural Institute of Canada, publisher2007-01-032007-01-031974-08Anderson, D. W., E. A. Paul, and R. J. St. Arnaud, Extraction and Charaterization of Humus with Reference to Clay-Associated Humus. Canadian Journal of Soil Science 54, no. 3 (August 1974): 317-323. https://dx.doi.org/10.4141/cjss74-041.http://hdl.handle.net/10217/80856An extraction-fractionation method was developed with which it is possible to isolate 60–67% of the humus of Chernozemic and Luvisolic soils. Two humic acid fractions were obtained: (1) a conventional alkali-pyrophosphate extractable HA-A; (2) a clay-associated HA-B fraction isolated after ultrasonic dispersion, in water, of the residue of the alkali-pyrophosphate extraction. As compared to the HA-A, the HA-B fractions had lower C contents but greater N contents, narrower C:H ratios, higher molecular weights, and less resistance to hydrolysis in 6 N HCl. It was concluded that the HA-B is a weakly humified, potentially labile humic constituent stabilized by adsorption to clay. Spectral measurements on low-ash (< 2 %) humic acids showed a positive correlation between extinction coefficient at 280 nm (E280) and C:H ratio, and negative correlations between E280 and percent of hydrolyzable C and N. The E4:E6 ratio was related to molecular weight, as determined by agar gel filtration, increasing with decrease in molecular weight.born digitalarticleseng©1974 Agricultural Institute of Canada.Copyright and other restrictions may apply. User is responsible for compliance with all applicable laws. For information about copyright law, please see https://libguides.colostate.edu/copyright.organic heteropolymerssoil organic matterextraction-fractionation methodhumusTexthttps://dx.doi.org/10.4141/cjss74-041