Should you inoculate your soil with microbials?

Wisconsin State Farmer
Soil fungi and bacteria are important for nutrient cycling and plant health.

Soil biology is an underappreciated aspect of agricultural systems. Soil fungi and bacteria are important for nutrient cycling and plant health and many can have a symbiotic relationship with crops, growing around or inside plant roots. Some microbes are so important that there may be benefit to adding them to soil at planting.

There is an increasing number of soil biological inoculant products. Many farmers and consultants may be considering their use, but aren’t exactly sure what they are or what their benefit would be. Three commonly sold inoculants are arbuscular mycorrhizal fungi (AMF), Trichoderma, and Bacillus amyloliquefaciens (BAA).

“Soil fungi such as AMF function as an extra root system for host plants and can increase P uptake from soil,” says Matt Ruark, Associate Professor of Soil Science at the University of Wisconsin-Madison/Extension. “Inoculation with AMF products can lead to faster root colonization of AMF, with greater potential for yield benefits in heavily tilled cropping systems or field that have been fallowed.”

Trichoderma (a species of fungus) and BAA (a bacterium) don’t live inside the plant root like AMF, but on roots or under root skin.

“The yield benefit of inoculating with Trichoderma or Bacillus will be beneficial when weather conditions are causing plant stress,” says Ruark. “However, there is limited field-based research in Wisconsin that demonstrates the economic value of inoculation.”

The efficacy of any of these products can vary significantly depending on field conditions, crop, and climate. University of Wisconsin-Extension scientists explain the products’ uses in three brief and easy-to-read articles that are available through the UW-Extension Learning Store. The articles can be downloaded and shared for free; they are also available as printed booklets for a nominal fee.

Direct links to the articles are:

The Value of Arbuscular Mycorrhizal Fungi for Field Crops:

The Value of Trichoderma for Crop Production:

The Value of Bacillus amyloliquefaciens for Crop Production: