Their definition. Humic substances have attracted the attention of soil chemists for over two centuries; in spite of intensive investigations, knowledge of the nature of these materials is still limited, however. Part of the difficulties experienced are caused by inaccuracy and inconsistency of definitions used. Over the years the terms humus, soil organic matter and humic substances have been redefined continuously. The large number of definitions has lead to many confusions and is partly caused by attempts of many investigators to relate definitions of these materials with their structural features. Because these materials have a very complex, mainly macromolecular nature it is understandable that analytical data of all kinds related to partial structures present in these materials are interpreted in many different ways.

21 pages, 6 figures, 2 tables, 34 references. Trabajo presentado por Cesáreo Sáiz-Jiménez en la tesis doctoral para la obtención del grado de doctor en la Technische Universiteit Delft.

This research has been funded by the C.S.I.C., Spain (Project No. 781).

Peer reviewed