Lumping or splitting: Holistic or fractionation approaches to studies of humic substances

Abstract

Some scientists (the 'Lumpers') argue that soils and especially soil organic matter should be studied in its entirety; others (the 'Splitters') choose to fractionate and study the component species or molecular entities. Though it is true that the agricultural and environmental functions of soils involve the holistic assembly of its components, many of the specific reactions and interactions involve components, both organic and mineral, that may be only a small fraction of the total assembly. In order to understand how the different species react and interact, it is therefore necessary to have an awareness of the surface properties of the species and of aspects of their compositions and structures. This is especially true of the organic components, and it is therefore necessary to study their abundances, properties, and interactions with other soil components. The present study shows how the compositions of fractions of humic extracts from two soils and from their drainage waters differ as the result of management practices. One soil is in long-term grassland, and the other is in long-term cultivation. Two humic isolation procedures were used: (1) the procedure for the isolation of the IHSS soil standards and (2) a modification of the resin procedure introduced by Malcolm and MacCarthy (Environ Int 18:597-607, 1992).