INFLUENCE OF ORGANIC-MATTER ON AGGREGATION IN OXISOLS RICH IN GIBBSITE OR IN GOETHITE .1. STRUCTURES - THE FRACTAL APPROACH

The structural implications of the influence of organic matter on surface charges in Oxisols were studied. Oxisols rich either in goethite or in gibbsite have irregular and self-similar aggregates of elementary ordered card-house-type assemblages of rigid kaolinite-goethite or kaolinite-gibbsite associations. The size of the elementary structural pattern decreases as a function of organic matter content and positive charge neutralization by organic matter which infills pores < 0.2 mum. The fractal approach also appears to be a useful tool for understanding the underlying mechanisms in the creation of Oxisol aggregates. The compactness of these aggregate structures increases towards the surface of the soil due to rearrangements during drying events of repeated wet-dry cycles. A correspondence between fractal interface and both aggregation kinetics during air-drying of wet aggregates and surface tension at the interface is suggested.