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ZUNINO H; APPELT, H; BERNARDI, C
Soil Science: July 1974
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ABSTRACTThe presence of humic acid B fraction in alkaline extracts of volcanic ash-derived soils (high in reactive aluminum) was studied. The humic acid B does not exist as defined organic matter in these soil extracts. Its formation as an insoluble fraction at pH 4.8 is due to an Al(OH)3 gelatin precipitate formation which adsorbs onto its surface the soluble fulvic acid fraction. The phosphate extracted by the alkaline extractant would be adsorbed on the Al(OH)3 surface in a similar way.The artificial formation of the so-called HA-B is easily avoided by eliminating the Al ions of the acid organic matter solution by means of a cation exchanger. In this way the extracted soil organic matter can be fractionated only into two really different fractions according to their solubility in alkaline or acid medium: humic and fulvic acids.

The presence of humic acid B fraction in alkaline extracts of volcanic ash-derived soils (high in reactive aluminum) was studied. The humic acid B does not exist as defined organic matter in these soil extracts. Its formation as an insoluble fraction at pH 4.8 is due to an Al(OH)3 gelatin precipitate formation which adsorbs onto its surface the soluble fulvic acid fraction. The phosphate extracted by the alkaline extractant would be adsorbed on the Al(OH)3 surface in a similar way.

The artificial formation of the so-called HA-B is easily avoided by eliminating the Al ions of the acid organic matter solution by means of a cation exchanger. In this way the extracted soil organic matter can be fractionated only into two really different fractions according to their solubility in alkaline or acid medium: humic and fulvic acids.

© Williams & Wilkins 1974. All Rights Reserved.