Chapter 15 - Interaction of Humic Substances and Soil Clays

Abstract

Adsorption is the controlling step that helps in the formation of microaggregates, as well as in the transport of nutrients and pollutants along the soil profile in many soils. Adsorption on soil colloids depends on the nature and properties of the surfaces available for interaction with ions and molecules present in the soil solution. Active sites on soil clays are masked by the presence of hydrous oxide material coating their surfaces and much of these surface particles are coated by humic substances. Thus, the complex soil colloids show surface properties attributable to clay, hydrous oxide, and humic compounds. These types of associations are present in soils to different extents. Residual products from the transformation of animal and plant remains as well as the products of the microbial degradation of organic materials added to soils as amendments are the origin of the naturally occurring components of the soil organic matter acting as component of soil aggregates. Humic substances (HS) and soil polysaccharides are the main active components of soil organic matter, which interact with the soil inorganic components in the formation of the organomineral complex as a base of the soil aggregates.