Formation of Soil Aggregates and Accumulation of Soil Organic Matter

Soil structure is the arrangement of particles in soil and the particles of sand, silt, and clay, bound together into aggregates of various sizes by organic and inorganic materials. The structural stability is the ability of the aggregates and pores to remain intact when subjected to stress, e.g. when aggregates are wetted quickly. In soils stabilized by organic matter, these stages of aggregation, or aggregate hierarchy, probably develop over many years, during the growth of roots, especially roots of grasses. Aggregation has been studied in at least two ways: the formation and stabilization of aggregates in suspensions of pure clay, and the separation of aggregates from soil disrupted by different amounts of energy. Microaggregates, which can be further divided into different sizes, are held together by different organic and inorganic materials. Microaggregates less than 2 im diameter have been studied in suspensions of pure clay, or have been isolated from soils subjected to ultrasound.