4 Key Tips for Choosing the Optimal Mycorrhizal Inoculant

Since the reintroduction of microbials in the early 2000s, farmers worldwide have been exploring the potential of microbial inoculants as a “natural crop insurance” to help increase yield and improve soil health in a sustainable manner. In the last few years, bioagriculture innovation has helped farmers maximize nutrient uptake while enhancing plants’ stress resistance to help achieve a “double bottom line” of both profit and sustainability.

When formed in 2013, the BioAg Alliance predicted microbials would be on nearly half of all U.S. corn and soybean acres by 2025. This prediction is playing out real-time. In May 2021, Research and Markets updated its growth projections for the agricultural biologicals market at a compound annual growth rate (CAGR) of 11.02% between 2021-2026 to reach a market size of US$19.6 billion in 2026.


As microbial innovation has become commercially available, farmers are readily adding biological solutions to their toolbox for immediate and long-term benefits. The market now consists of many products with a variety of formulations and ingredients – often making it difficult to compare the efficacy and ROI of available options. The first step is understanding the relationship between plants’ root systems and the microbials that surround them in the soil.

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The microbial family contains a range of beneficial fungi; among the most prominent are mycorrhizae – the “queen of biologicals.” Mycorrhizae do more than attach to plant roots – they weave a supportive foundation for microbial network growth throughout the soil. Mycorrhizae are the infrastructural linchpin supporting entire microbial ecosystems, including helpful bacteria called mycorrhiza helper bacteria, that form symbiotic relationships with fungi and support plant growth. In fact, a whole forest connected by the mycorrhizal web can comprise of a single organism. The mycorrhizal filaments – called hyphae – construct biological superhighways funneling nutrients to plants in the most efficient, effective, and natural way. Mycorrhizae release otherwise inaccessible phosphorus for plant uptake in three critical ways:

  • first, by literally unlocking the bonds that phosphorus forms with the soil;
  • next, by transforming its molecular structure into one available to the plant, and
  • finally, by mobilizing it through the hyphae and into the plant roots.

Commercial use of chemical fertilizers since the 1940s depleted and damaged many fungi, including the vast network of mycorrhizal filaments. Since the development of mycorrhizae in agricultural settings can be triggered or encouraged with specifically tailored inoculants, new solutions were needed to deliver commercial scale products at the right price point.

Mycorrhizal inoculants are penetrating mainstream agriculture thanks to extensive research and development by companies like Groundwork BioAg. For the past several years, Corn Warrior and PodFathers podcast star Corey Atley, who grows corn and soybeans on his 8,000-acre farm in Ohio, earned the National Corn Growers Association’s yield contest after integrating mycorrhizal inoculant, Rootella, to improve his yield by 4-12 bushels per acre in corn and above 90 bushels per acre in soybeans. Today, growers can choose the right inoculant for their operations knowing that the benefits of mycorrhizae are cumulative beyond a single crop or season.

Here are tips for choosing the optimal mycorrhizal inoculant:

  1. Know your Soil: The right microbial can balance out chemical overuse, strengthen stressed plants and restore soil fertility. Insight into what your soil lacks will help further define your need. For example, mycorrhizal inoculants are essential to maximize phosphorus uptake and save on fertilizer.
  2. Concentration is Key: Product labels often include concentration in terms of spores or propagules per gram. A propagule is a structural unit of fungus that forms symbiosis with plant roots. Spores, however, are simply one type of propagule. Propagules can include spores, hyphae and inoculated root fragments. Whether in terms of propagules or spores, the best indication of inoculant potency is the concentration – the number of propagules or spores per gram of mycorrhizal species relevant for specific crops. Some products on the shelf offer 5-10 spores per gram, while only a few have achieved a concentration of thousands per gram or more. To ensure that an inoculant’s potency aligns with expectations, the concentration count must be clear, accurate and high.
  3. Beware of Misleading Labels: Not all mycorrhizae are created equally. Some list “mycorrhiza” on their labels while barely containing any or the right kind of the fungi in the product. Of the two relevant types of mycorrhizae – endo– and ecto-mycorrhizae – ecto-mycorrhizae associates with woody plants (trees and bushes) and offers no value for other crops. For row crops, only endo-mycorrhizae are beneficial, therefore that is the most important ingredient on the label.
  4. Mycorrhizae Should be User-Friendly: Many mycorrhizal inoculants are formulated to be used in conjunction with specific usage techniques and methodologies, such as drip irrigation or seed boxes. A quality mycorrhizal inoculant should allow for a range of application methods that allow for farmers to maintain their cultivation practices for each acre with the strongest concentration of mycorrhizal propagules per gram.

The ideal mycorrhizal inoculant will ensure a positive ROI for crops, soil, and the planetary biosphere. As a result, farmers can achieve higher yields with a natural crop insurance. Choosing the optimal mycorrhizal inoculant can literally bring life back into the soil, allowing farmers to let their ground work.