Q&A with Anissa Poleatewich

How do mycorrhizae interact with fertilizers?

Understanding the implications of mycorrhizal fungi with fertilizers, fungicides or pesticides comes down to understanding the basics of how fungi interact with plants and what governs that interaction. Mycorrhizal fungi form associations with plant roots; they actually grow inside of the plant roots. However, the plants dictate the formation of that association. When the plants are in need or in stress, they’re more likely to form that association faster because these fungi help plants tolerate stress and acquire water and nutrients such as phosphorus. The fungi help plants access areas of the substrate or the soil that the roots can’t reach, or that are not in a form that is available to the plant. However, when phosphorus is in excess, it can slow the formation of that relationship between the plant and the fungus. The plant doesn’t need phosphorus because there’s plenty around.

How should growers handle that interaction?

Best practice for using mycorrhizal fungi and fertilizers is to choose one that has a lower phosphorus amount in your NPK ratio so that you don’t hinder or slow the formation of mycorrhizae. You might consider reducing the parts per million of phosphorus compared to nitrogen, particularly in the early phases of when you’re applying the mycorrhizal fungi and you want the association to form. The early phases of when the root-fungus relation is forming is crucial and when the fungus is helping to provide the plants with nutrients is an important time you wouldn’t want to slow by having excess fertilizer.

What are the benefits of mycorrhizae and fertilizer working together?

When using fertilizer levels within the range of what the plant needs and the association has formed, you’ll start to see the benefits which include enhanced efficiency at which the plants utilize the fertilizer. For example, in container production once the mycorrhizal fungi have established themselves in the plant roots, there is less loss of nutrients from leaching. Part of that is because the hyphae of the fungus are transporting the phosphorus to the plant, but the other reason is as the hyphae grow through the soil and the substrate, they improve soil structure and allow the substrate to hold on to water and nutrients better. So you not only lose less fertilizer, but you lose less water as well. Going forward, you’re actually improving the efficiency of your investment in that fertilizer as opposed to losing it through the leach. That’s along with the benefits of improved root growth, above-ground growth and higher tolerances to stress that comes with mycorrhizal fungi.

How do you create the environment where they can work together?

The nice thing about it, is it is not overly difficult or complex to get mycorrhizal fungi to work in production. There are just a few scenarios where you’re encouraging the plant to allow this fungus to infect the roots. If you provide those conditions, then that association will form. It’s very similar to conditions you provide for encouraging other microbials, like bacterial biofungicides or entomopathogenic fungi as bioinsecticides. The key is to create the environment for beneficial microbes to be able to do their job.

For more: mycorrhizae.com

Questions? Anissa.Poleatewich@mycorrhizae.com