Soil Colloids and Soil Organic Matter Associativity - the Basis of Soil Structure

Abstract In the hierarchical model of soil structure, the lowest scale of structure is the combination of clays < 0.2 um diameter to form 2 um domains. to investigate the basis for soil structure, two highly weathered soils from Brazil (Oxisols) were selected and the < 2 um size fraction extracted by sedimentation for analysis. The first soil used in this study, classified as Xanthic Hapludox, was collected in 1991 at an EMBRAPA research station outside of Manaus, Brazil from a tropical forest site collected from the 0-8 cm depth. The second soil (0-20 cm depth) was sampled from a topographically flat area inside the Brasilia National Park, Brasilia D.F. Brazil by Dr. Flavio Vasconcelos. The samples were analyzed by NMR spectroscopy, transmission electron microscopy, atomic force microscopy, and scanning electron microscopy. NMR spectroscopy revealed the organic materials within this size fraction consisted predominantly of polysaccharides.