Organo-mineral complexes and their effects on the physico-chemical properties of soils

A wide array of organic compounds, including HS, PS, amino acids, peptides, proteins and aliphatics are adsorbed to the soil's mineral components, clay and hydroxides in particular, to varying degrees, thereby playing an important role in the determination of aggregate stability. Adsorption is determined to a large extent by the properties and charge of the organic and mineral components, pH, ionic strength and the nature of the exchangeable cation on the clay surface. Organic substances of microbial and plant origin cement the soil particles together to form macro- and micro-aggregates. Plant residues and PS play a dominant role in determining the stability of macro-aggregates while HS including humin are more important when micro-aggregates are of concern. Integrating all these effects influences the physical properties of soils. Coating of micro-aggregates or sand particles with DOM, HS or charred soil OM, under slow air drying can induce water repellency which, although considered a negative property of soils, will stabilize soil aggregates.