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BIOLOGICAL INOCULANTS

In the past decade we have learned a great deal about plant Mycorrhizal fungi (MF) are fungi that live on and within
species, their use as cover crops, and how they can create plant roots in a mutually beneficial relationship, and extend
healthier soils. We have learned that soil improvement root -like structures called hyphae that reach out as far as
comes primarily from soil microbes, and that one of the 18 inches past the root zone to obtain water and minerals
primary contributions of cover crops is to feed soil mi- for the host plant that plants alone cannot access. MF also
crobes. We actually know very little about those soil im- exude a substance called glomalin, a powerful soil aggre-
proving microbes; even the best soil microbiologists only gating compound that is more persistent than other forms
understand a small fraction of what goes on in the soil of soil organic matter. MF are present in all natural eco-
(see pages 46-51 for more biology information). We may systems, but are usually lacking or in very low numbers in
not know what individual microbes are doing and how tilled or fallowed cropland, because MF need a living host
to manage them on a species by species basis, but we can root to live. It is important to realize that MF are not a magic
apply some general principles that encourage the growth potion, but they can enhance yield by helping access addi-
of microbes in general and to consider using microbial in- tional water and nutrients. The best responses to inocula-
oculants when it makes sense. tion will result when natural populations of MF are lacking,
There are literally thousands of companies that sell “bugs as in a field with a history of tillage or long fallow periods,
in a jug” products. Most of these products have some le- and when moisture or minerals are lacking. Heavy clay soils
gitimate value, but some have such low concentrations that show the most improvement over time from the exuded
they can’t make a difference. Most commonly, though, the glomalin. Crops that respond best on a “dollars returned
soil has simply not been managed to provide good microbi- for dollar invested” basis are perennial crops like alfalfa and
al habitat. It is important to understand that it is impossible new seedings of perennial grasses, as the MF lives as long as
to simply inoculate your way to soil health, but we must the host plant, so a single inoculation can last several years.
create the conditions that promote healthy microbial pop- Another high return scenario from a single inoculation is
ulations - which happen to be the same as the principles of to inoculate at the beginning of a crop rotation featuring
soil health: limited soil disturbance, soil cover, year-round continuous living roots from a sequence of cash crops and
living roots, plant diversity, and livestock integration. Mi- cover crops.
crobial inoculation will provide the most visible benefits on
degraded soils that are having soil health principles applied.
At Green Cover Seed, we are constantly evaluating and ex- Photo by Wendy Taheri
ploring biological inoculants and any inoculant we choose
to put on the market must provide more dollars of benefit
than it costs. Our offerings will change as we learn more
about which products provide clear economic benefit and
fit well with the use of cover crops. We are always eager for
our customers to try out new biological products and give
us their honest feedback after doing due diligence to accu-
rately measure value.

In addition to rhizobium inoculants for legumes (which
few people question the value of), we offer several microbial
inoculants which we feel are useful. Wendy Tahari, one of the top soil microbiologists, also

points out that MF feed and support other soil microbes
that benefit the crops. When systems are managed to sup-
port MF, other beneficial organisms increase as well, and
less fertilizer and fewer inputs are required, as the diversity
that comes along with good management promotes plant
Photo by Brett Peshek health while creating competition that helps to keep pests

under control. Most agricultural chemicals have a negative
impact on soil microbes, so save them for the real emer-

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