Soil aggregation

Soil aggregation is the binding of mineral particles and organic matter into clusters called aggregates. Aggregate size and stability shape soil structure, pore space, and water movement.

Soil organic matter: The mixture of decomposing and living organic materials in soil, including plant residues, microbes, and humus. Decomposition products and organic compounds help cement particles into stable clusters.
Soil texture: Soil texture is the relative proportion of sand, silt, and clay-sized mineral particles. Texture sets the particle sizes available to assemble into aggregates.
Wet sieving: Wet sieving measures soil aggregate stability by exposing aggregates to water and separating them by size. It provides a common laboratory measure of resistance to slaking and breakdown.
Infiltration (hydrology): Infiltration is the entry of water from the ground surface into soil. Aggregate arrangement and connected pores affect how quickly water enters.
Soil aggregate stability: Soil aggregate stability is the resistance of soil clusters to forces such as wetting, raindrop impact, and tillage. It is a central outcome, but measurements depend on the disturbance and method chosen.
Soil fungi: Fungi are organisms that grow as networks of microscopic filaments and decompose or exchange nutrients in soil. Fungal hyphae physically enmesh particles and can connect aggregates.
Soil structure: Soil structure is the arrangement of soil particles into aggregates and the spaces between them. Aggregation is the process that produces key units of soil structure.
Mean weight diameter: Mean weight diameter is a weighted average of the sizes of soil aggregates in a sample. It summarizes aggregate-size distributions measured by sieving.
Water-stable aggregates: Water-stable aggregates are soil clusters that resist disintegration when wetted. Their persistence helps maintain pore networks during rainfall and irrigation.
Slaking: Slaking is the rapid breakdown of dry soil aggregates when they are suddenly wetted. It links wetting conditions to aggregate failure and water-stability measurements.

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