1. MACROMOLECULAR PROPERTIES OF SOIL HUMIC SUBSTANCES: FACT, FICTION, AND OPINION
2. MOLECULAR WEIGHT AND SHAPE OF HUMIC ACID FROM SEDIMENTATION AND DIFFUSION MEASUREMENTS ON FRACTIONATED EXTRACTS
3. M. M. Kononova , Soil organic matter, its nature, its role in soil formation and in soil fertility , Pergamon Press , New York, NY , 1961
4. F. Stevenson , Humus chemistry: Genesis, Composition, Reactions , Wiley , New York, NY , 2nd edn, 1994
5. A. Piccolo , in Advances in Agronomy , Elsevier , 2002 , vol. 75 , pp. 57–134