In this webinar we go in-depth and learn more about how aggregates are an important part of a healthy soil. We’ll start with the basics of how aggregates form, what stabilizes them and how they naturally turnover with time. We’ll also talk about how to evaluate aggregation using a shovel in the field along with options for analyses in the lab. The benefits of stable aggregation are not just physical, but also biological. This is part of why aggregation can be a great indicator of a healthy soil. Knowing what aggregates can do for you and how to manage for this part of the system when it comes to achieving on-farm goals really shows the importance of this soil property.

1 CEU in Soil and Water Management.

Presenter: Abbey Wick, Soil Health Extension Specialist, North Dakota State University

Sponsors: Illinois Soybean Association, North Dakota Soybean Council and North Dakota Corn Utilization Council

Aggregates: Groups of soil particles that bind to each other more strongly than to adjacent particles.
  • Respond to changes in management
  • Combination of sand, silt, clay, animal-derived debris and other organic material
Functional vs. Non-functional Aggregates
  • Functional create great habitats for microbes
  • Functional give more stability to the soil, have more pore space, and more water-holding capacity and air space
Aggregates Based on Function
  • Microaggregates are primary soil particles that are pulled together by physical-chemical forces
  • Macroaggregates are greater than 250 microns—form from organic debris and microaggregates
    • Fine roots and fungal hyphae will wrap around and stabilize
  • Microaggregates are held together by microbial glues; macroaggregates are held together by fungal hyphae
Aggregates Based on Size
  • Dr. Johan Six – for western U.S.
    • Less divisions because western U.S. doesn’t form aggregates as easily because it’s drier
  • Dr. Julie Jastrow – out of Illinois
Aggregates and Farm Systems
  • More large macroaggregates in pasture converted to corn system
  • More microaggregates in conventional tillage row crop system—create really tight pore spaces, not a lot of room for water to infiltrate soil
  • Balance of aggregates in no-till, cover crop, row crop system
Aggregate Formation, Stabilization and Disintegration
  • Aggregates are meant to turn over
  • Formation happens when primary soil particles and organic matter are held together by fungal hyphae
  • Fungal hyphae and roots pull particles into stable aggregates
  • When aggregates are stable, wet-dry cycles pull aggregate closer together
  • Microbes eat organic matter and aggregate disintegrates
  • When the aggregate breaks down it releases organic matter into the soil
    • Tillage shortens aggregate cycle
  • Aggregates can also form from earthworms. The soil minerals mix in their digestive system and are excreted

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