Extraction and charaterization of humus with reference to clay-associated humus
An 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 ...
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