Aggregation in soils with small amounts of swelling clays. I. Aggregate stability

SUMMARY The respective role of organic materials and poorly‐ordered Al and Fe hydrous oxides on soil aggregate stability was studied in silty soils with little swelling clay, using both multivariate analysis and physico‐chemical approaches. Soil disaggregation is a function of the hydrophobic character of organic matter (OM), which depends on the nature of the organic materials, cationic environment and the aggregating effect of Al and Fe hydrous oxides. Two kinds of aggregates >50 μm can be distinguished in organic soils, one being about six times more stable than the other. In soils poor in organic matter, weak aggregates dominate; the binding agents are Ca or Al OM rich in polysaccharides and peptides.