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Aggregate Stability

  • Soil Health

  • Physical

Summary

Aggregates, formed through interactions among soil biota, plant communities, and soil mineral components, consist of multiple soil particles bound together. These structures play a pivotal role in various aspects of soil health, influencing water movement, storage, soil aeration, physical protection of soil organic matter (SOM), erosion prevention, root development, and microbial community activity (Arias et al., 2005).

The vulnerability of soil aggregates to external forces is quantified through aggregate stability (Arias et al., 2005). Aggregate stability involves microorganisms producing glues, such as soil carbohydrates, which, along with fungal hyphae and fine roots, contribute to binding the aggregates. Soil aggregation integrates biological, chemical, and physical soil properties, and serves as a vital indicator of soil health (Stott, 2019).

The breakup of soil aggregates can result in oxidation, leading to a subsequent reduction in soil organic carbon (SOC). This also brings about a decrease in mean pore size, reducing plant-available water, plant growth, and microbial biomass and activity, through an increase in bulk density and a decrease in macroporosity (Merrington, 2006).

Methodology summary

The easiest way to measure aggregate stability on-site is to use the Emerson test:

  • Select 3 air-dry aggregates, 5–10 mm diameter.
  • Place 75 mL deionised water in a container. Place the 3 aggregates in the container of water, spaced equally around the side. Do not stir or otherwise disturb.
  • Record the time placed in the water. After 2 hours and 20 hours, assess aggregate behaviour according to the following:
    • Record whether the aggregate has disintegrated. If there has been no disintegration, record if there has been any swelling of the aggregate.
    • If the aggregate has dispersed, note the degree of dispersion.

For more detailed information watch the following video and read the following instructions from the New South Wales Government:

Metric threshold or direction of change

A Mean Weight Diameter (MWD) of 2 mm is regarded as optimal for both productivity and environmental well-being. A decline in MWD below 2 mm, or even reaching 1 mm, is seen more as an environmental concern (Merrington, 2006). There is a consensus that the trend in aggregate stability aligns with the “more-is-better” principle (Stott et al. 2019), as the higher proportion of stable aggregates with a MWD of around 2mm can be associated with environmental well-being.

Technological innovations

Laser diffraction method shows promising agreement with the wet sieving method, whilst having a faster processing time and lower variability of results (Gyawali & Stewart, 2019; Kubát et al., 2022).

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  • Agricultural
  • Forest
  • Grassland
  • Peatland
  • Saltmarsh
  • Wetland

Scale

  • Community

Cost

  • Low

Tier

  • Tier 2

Technical expertise

  • Low

Standardised methodology

  • No