Q&A

DEAR NEW FARM:

I understand mycorrhizae fungi are subject to pH but I have not found an article saying what the parameters are.

Lou Doering
Florida

DEAR LOU:

We posed the question to Rodale Institute research agronomist Dave Wilson. Here’s what Dave had to say.

We don’t have any specific pH parameters for mycorrhizae fungi. This is what we do know:

In most well-aerated soils, fungi are the largest fraction of microbial biomass. In general, soil fungi exist over a wide pH range but are more tolerant of acid soils than are other microorganisms. Consequently, to select fungi instead of other microorganisms, people use a media that has an acidic pH.

But, if the soil solution is too acidic, plants cannot utilize N, P, K and other nutrients they need. The optimum pH range for most crops is 6.0-7.5 and for leguminous and other alkaline preferring crops, 6.5-8.0. Since the mycorrhizae need to infect the root and carry on symbiosis with living root material, it would stand to reason that the pH range most optimum for any given crop is also the pH range most optimum for the mycorrhizae types that infect that crop and live in symbiosis with it.

Note: High rates of fertilizers, especially phosphorus, inhibit the formation of mycorrhizae; organic forms of fertilizers seem to have less inhibitory effect on mycorrhizae than inorganic, soluble fertilizers.

As per our Fact sheet Improve Your Soil, increase your Yields, and Reduce Your Expenses with AM Fungi, we list the following steps to cultivate your soil’s native AM fungus population.

1. Don't fertilize with phosphorous. The benefits of mycorrhizae are greatest when soil phosphorous levels are at or below 50 ppm. Mycorrhizal infection of roots declines above this level with little if any infection occurring above 100 ppm P, even when soil is inoculated with a mycorrhizae mix.
2. Don't till more than necessary.
3. Don't let fields lie fallow in winter.
4. Do plant a cover crop.
5. Do develop a diverse crop rotation.
6. Do grow crops that support AM fungi.

NF

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