Often, we focus our understanding of soil biology on invasive, harmful pathogens. However, within soils are numerous beneficial microorganisms vital to crop development. Mycorrhizae fungi make up such a segment of soil biology, critical to the overall supply of water and nutrients to many crops.

“Myco” – “rhiza” translates to “fungus” – “root.” These beneficial fungi form a symbiotic relationship with plant roots resulting in the development of hyphae (fungal root extensions). The plant manufactures organic molecules such as sugars via photosynthesis and supplies them to the fungi; in turn, the fungi then supply the plant with water and mineral nutrients, such as phosphorus, taken from the soil. The formation of hyphae, which are much smaller in diameter than root hairs, allows for access to pore space in which roots cannot. This increased area of accessibility provides a greater supply of water and nutrients. Hyphal extensions also significantly increase the overall root surface area. Studies have shown that mycorrhizae and the formation of hyphae can make up as much as 10 to 20% of the total root mass1. While roots play a role, the mycorrhizae fungi that live on the roots and in the soil serve as an essential means for bringing water and nutrients into the plant through the roots.

Why Soils Vary in Colonization, Hyphae Formation

The relationship between mycorrhizae and plants is mutually beneficial (or symbiotic). As the requirement for water and nutrients increases, the plant roots emit a biochemical invitation for mycorrhizae inoculation. The accepted request by soil mycorrhizae then results in root colonization, thus the formation of hyphae. Inversely, mycorrhizae fungi require plant roots to acquire sugar, carbohydrates necessary to survive. Endomycorrhizae, the classification of mycorrhizae associated with corn, soybeans, and wheat, live within root cells on carbon provided by plant roots. Without a host or plant material, mycorrhizae populations collapse.

Any circumstance that impairs pore space or oxygen levels can negatively impact the mycorrhizae community compaction, flooding, tillage (thus reduced soil aggregation), soil texture, or magnesium content. Acres that remain fallow for a period of time can significantly impact mycorrhizae populations.

Hyphae root extensions provide increased access to soil water and nutrients but also serve as a web to increase aggregate stability and water infiltration. On the surface of hyphae is the abundance of a glycoprotein substance known as glomalin. Glomalin serves as the “glue,” helping to bind soil particles together, allowing for greater water infiltration with intense rainfall. Glomalin is also a significant contributor to overall soil carbon. Carbon is a food source for many microorganisms. As a carbon source, glomalin biodegrades slowly over time and has been shown to persist for up to 40+ years in the soil, depending on climate and other soil parameters. Fungi are a major factory for converting soil carbon into soil organic matter (SOM). Each 1% of SOM equates to ~ 27,000 gallons of water holding capacity per acre or nearly an acre-inch of rainfall2.

Increase water availability - formation of hyphae, increased root surface area

Increase nutrient uptake - particularly N, P, and S

Improve aggregate stability → increases water infiltration

In Today’s Climate, is Traditional Fertilization Sufficient?

While the annual rainfall volume of some areas has increased slightly in recent years, the intensity at which we receive rain has changed dramatically. Extreme, vicious rains today are commonly proceeded by prolonged dry periods. Sporadic weather patterns have not only changed how we receive precipitation but also our soil's ability to accept and retain moisture received. Intense rains have also resulted in the net effect of increased soil bulk density, thus reducing nutrient accessibility. Adapting to changing weather patterns and maximizing soil water and nutrients may require supplemental mycorrhizae within certain management practices, soils, and situations.

Supplementing Mycorrhizae Will Have a More Significant Impact:

Lower water-holding capacity soils — ↓ OM (≤ 3%), sand, gravel, tight clays

Lower fertility soils - especially phosphorous

Tight, root-restrictive soils - ↑ magnesium content (> 20% base sat.), clay texture 5. Corn hybrids requiring more N and S later in development

The pictures below are from on-farm trials conducted utilizing EndoPrime SC™, which contains four different species of mycorrhizae fungi. All the trials were evaluated in a corn-after-soybean rotation, non-fallow acres.

1. https://dl.sciencesocieties.org/publications/jpa/abstracts/11/2/200?access=0&view=pdf