Microaggregate

Microaggregate is a term used primarily in soil science and sedimentology to describe small, cohesive clusters of mineral particles bound together into a single particle. In soils, microaggregates are typically less than 0.25 millimeters in diameter and form a key part of the soil’s microstructure, coexisting with larger macroaggregates. They consist of mineral particles cemented by organic matter, clays, iron and aluminum oxides, and biological products produced by plants and microorganisms.

Formation of microaggregates occurs through physical, chemical, and biological processes. Plant roots, root exudates, and microbial byproducts such as fungal glomalin and other organic polymers promote binding. Clay minerals can act as cements, and multivalent cations like calcium, iron, and aluminum help bridge particles. Wetting and drying cycles, soil fauna activity, and long-term inputs of organic matter contribute to the development and stabilization of these tiny aggregates.

Microaggregates play a major role in soil function. They help stabilize soil structure, influence porosity and water infiltration, and protect soil organic matter from rapid mineralization, contributing to long-term carbon storage. They also affect nutrient cycling and availability, particularly for micronutrients, and can influence erosion resistance and soil fertility. Management practices such as reduced tillage, cover cropping, and organic amendments tend to enhance microaggregate stability and buildup.

Analytical approaches to microaggregates involve separating soil fractions by size and dispersion techniques, followed by measures of aggregate stability and composition. In other fields, the term can refer more broadly to small particle aggregates in sediments or composite materials, reflecting a common concept of tightly bound particle clusters.