Nets and Glues: How Microbes Build Soil Structure

Sponsored by Heliae® Agriculture

Does your soil sometimes seem more likely to make pottery than grow crops? Or does it feel like trying to build a sandcastle out of dry sand? If so, you may need to pay more attention to the fungi and bacteria living below the surface. These microorganisms release substances which act as nets or glues, building soil structure by forming and stabilizing soil aggregates.

Aggregates are the Foundation of Soil Structure

An aggregate, in technical terms, is “a group of primary soil particles that cohere to each other more strongly than to other surrounding particles.” But what does this mean in the field? Depending on your soil’s texture, fertility, and carbon content, soil particles and microbes mesh together to form 3 dimensional shapes, primarily determined by the products of living and dead bacteria and fungi in the soil.

Aggregates are essential to many basic functions of soil, from holding on to nutrients and preventing erosion, to supporting root systems and avoiding water stress. These functions are strongly tied to the soil microbiome, where a healthy community of bacteria and fungi provide support for optimized crop growth. The sticky qualities of many microbe products can directly hold on to nutrients and soil particles. Indirectly, through creating aggregates, improved soil structure encourages root development and moderates water content.

An aggregate, in technical terms, is “a group of primary soil particles that cohere to each other more strongly than to other surrounding particles.”

Bacteria and Fungi in the Soil

Bacteria in soil tend to live in aqueous environments, moving with water in the soil. They can be single cells, moderate groups, or most important for aggregation, large populations living in biofilms. Bacterial cells attach to and digest pieces of organic matter, producing weak glues in the process that attach to a few surrounding soil particles. Over time and around larger pieces of organic matter, some bacteria will form biofilms or secrete sticky and slimy polymers called EPS (extracellular polymeric substances). These can act as stronger glues in the soil, attaching soil particles together to form aggregates and maintain water content in the soil.

Beneficial fungi have a slightly different role in building aggregates, acting more as nets than glues. Fungal mycelia (the vegetative parts of the organism), consisting of a complex network of branching hyphae, act as a major decomposer in the soil ecosystem. These networks also help to physically attach small aggregates, wrapping them up to form larger aggregates in the soil. Even when a branch of fungal hyphae is severed or otherwise begins to decay, this supports aggregate formation. During decomposition, biomolecules such as glomalin[KW1]  and mucilages are released from the cell walls. These substances are resistant to decomposition and can remain in soil for up to 50 years. Due to the nature of fungal hydrophobicity, fungi help aggregates stay together during rewetting by preventing water from penetrating deep into the aggregate. This reduces stress and swelling forces within small and large aggregates and lends stability to soil structure.

Microbes and Soils – Partners in Field Quality

Soil structure in agricultural soils is degrading at an alarming rate, with up to 30% of cultivated soils around the world considered degraded or eroded land in 2020[KW2] . Intensive agricultural practices can negatively affect microorganisms that do work in your field to create and stabilize soil aggregates. By improving the below-ground ecosystem, bacteria and fungi can rebuild their communities and build your soil’s structure along the way

Soil acts as the foundation for your crops, but the microbes in that soil are essential to keeping it well-structured and healthy[KW3] . The biological ecosystems beneath the surface work with your soil to provide structure and promote the health of your crops. Regardless of your soil type or organic matter content, bacteria and fungi are an essential building block in your field’s structure and the health of your crops. And working to strengthen them will improve your soil’s structure and overall field health.

For more on EPS and soil health, join authors, Lindsay Vicars, Dr. Karl Wyant and other leadership from the Heliae® Agriculture team, at “Rethinking Soil Productivity”.

The 2-day webinar event kicks-off November 17 at 10 a.m.-11:00 a.m. CDT with a conversation on the Rhizophagy Cycle with Rutgers University’s Dr. James White. Day 2, November 18, 10:00-11:00 a.m. CDT offers practical application opportunities for soil health practices. Following the main session each day, regional, crop-specific breakout sessions will be offered.

The event will also offer 4 Certified Crop Advisor CEUs in the following certification areas:

Nutrient Management: 1
Soil & Water Management: 1
Crop Management: 1
Professional Development: 1

For more information and to register for sessions, visit: https://phycoterra.com/2020/09/23/heliaeagriculture-presents-rethinking-soil-productivity-a-2-day-webinar-for-growers-innovators-investors/

References:

  1. https://www.sciencedirect.com/science/article/pii/S0944501315300288
  2. https://www.sciencedirect.com/science/article/pii/B9780124095489050879
  3. https://www.sciencedirect.com/science/article/pii/S0065211316301122
  4. https://www.ars.usda.gov/ARSUserFiles/30640500/Glomalin/Glomalinbrochure.pdf
  5. https://www.sciencedirect.com/science/article/pii/S0038071720300638
  6. https://ohioline.osu.edu/factsheet/SAG-10

 [KW1]I added a USDA glomain link here

 [KW2]I added the FAO erosion page link here

 [KW3]Well said