Fungi must be present to perform their functions of competing with the more
difficult disease-causing organisms, retaining nutrients especially micronutrients
like calcium, and making macro aggregates which form air passageways and hallways
to allow air and water to move through the soil. This is a critical step
in improving soil structure, but cannot occur without the first step of good
The “correct” density of fungal biomass, or amount of fungal
activity, is just now begun to be understood based on observation in different
soils, climates and plant species. Seasonal variations and the requirements
of different plants appear to be the most important factors.
When total fungal biomass is too low, fungi must be added back into the soil
using either compost, compost tea. Alternatively, these fungi might be found
in healthy soil, especially the humus layer of a healthy forest. But be careful
not to destroy that resource by removing too much, or disturbing too much.
When total fungal biomass is high, most of the time this means improved
ability to perform fungal functions, but if the balance between total bacteria
and total fungi becomes inappropriate for the plant species, then the balance
needs to be restored. However, you don’t kill off fungi if they are
higher than the desired ratio, you improve bacterial biomass instead.
On rare occasions, total bacteria may compete with fungi for food resources,
and in this case, reducing bacterial foods may be a good idea, to allow
the fungi to have a chance to grow. High total fungal biomass, combined
with too low active fungal biomass may indicate a fungal disease outbreak
in progress. This can be confirmed by examining the roots for necrosis,
galls, or other signs of fungal disease.
Beneficial fungi require aerobic
conditions and if oxygen falls below 5 — 6 mg oxygen per liter, then
the beneficial fungi may not survive. Anaerobic bacteria attack and consume
fungi in these low oxygen conditions. Disease-causing fungi are benefited
by anaerobic conditions, either because they no longer have competition
from the beneficial's, or because they require anaerobic conditions for
best growth. In either case, anaerobic conditions select for and allow
the disease-causing organisms to “win” in
the fight for plant tissues.
Providing supplemental food for improved fungal activity
Just like any other creature, fungi require food. Feed the beneficial fungi,
if fungal activity is too low. Sloughed root cells and dead plant tissue
often supply the more complex carbon substrates that fungi require, such
as cellulose, cutins, lipopolysaccharides, complex protein-sugar-carbohydrate,
and lignins. Fungi are good at condensing organic matter into ever more complex
forms, such as fulvic to humic acids.
Fungi need N, P, K, Ca, and all the other nutrients as well, and obtain
those from organic matter as well as from inorganic sources. Many species
of fungi can solubilize mineral elements from the mineral components of soil,
but no one species effectively solubilizes ALL minerals. A diversity of species
is needed to obtain all nutrients.
Often soil tests will indicate that some nutrient is in low supply, but merely
by adding the appropriate bacterial or fungal species, these organisms will
convert plant unavailable nutrients into plant available forms.
Diversity is the key, as well as feeding that diverse set of species so
they will perform their functions.
Both bacteria and fungi are important in holding nutrients in the soil when
they would otherwise leach into deeper soil layers, and into ground water.
The importance of microbes in forming soil structure and preventing erosion
is well-known, but in order to hold the nutrients in soil, bacteria and fungi
must turn them into biomass, which is not-leachable as long as the glues
and strands that the fungi and bacteria use to hold themselves on any surface
are not destroyed.
If activity is low, then fungal foods need to be added to increase growth
rates and improve numbers. A diversity of foods needs to be added, and
thus dead leaf material is a much better choice than purified cellulose.
Fish hydrolysate also adds bacterial foods, and N and other micronutrients.
Wood, sawdust, bark, paper and cardboard can be used as well, but diversity
If activity is higher than the desired, then try to balance the ratios
of the organisms by improving the organism group that is too low.
If active fungal biomass is low, but total fungal biomass is high, this
is a good indicator that disease is either rampant, or about to be rampant.
Add BENEFICIAL fungal foods and build soil structure as rapidly as possible
to compete with the disease, and protect the plant roots from the disease.
In rare instances, it may be because some environmental disturbance occurred
that put the majority of the fungi to sleep, but did not kill them.
The percentage of the root system that must be colonized has not been fully
established in the mycorrhizal literature, mostly because determining benefit
is relative. Mycorrhizal fungi can protect the roots from disease organisms,
through simple spatial interference, by improving nutrient uptake, and by
producing glomulin and other metabolites that inhibit disease. Stress in
plants can be reduced because the mycorrhizal fungi can solubilize mineral
nutrients from plant not-available forms to plant available forms, and translocate
those nutrients to the root system in exchange for sugars provided by the
Given that mycorrhizal fungi can influence so many aspects of plant growth,
and documenting all these benefits is usually extremely expensive and difficult,
they have not been documented. Therefore, probably the best that can be done
is to say that perhaps as low as 12% colonization might be documented to
be beneficial (work by Moore and Reeves in the mid-1990’s), but more
likely a minimum level of 40% colonization is required, as suggested by Mosse,
and St. John in various publications and comments.
Early researchers found colonization as high as 80% in root systems, but
most likely because they did not differentiate false-arbuscular and vesicular
structures produced by disease-causing fungi from true VAM structures. Thus,
colonization is rarely as high as 80% is not commonly found now that we recognize
these non-mycorrhizal forms.
In the last 10 years, some researchers have suggested that some mycorrhizal
fungi do not produce vesicules under all conditions, and so VA mycorrhizal
fungi should be called arbuscular mycorrhizal fungi, not vesicular-arbuscular
mycorrhizal fungi. Just be aware that sometimes, people say VAM, sometimes
If the plant does not require mycorrhizal colonization, there probably
is no reason to assess the roots for mycorrhizal colonization. Although
the Allens showed that one way for certain plants to exclude non-mycorrhizal
plants from a community was to make sure the mycorrhizal fungi were present,
because the mycorrhizal fungi pulled nutrients from the non-mycorrhizal
plants. This is a probable mechanism for mycorrhizal crop plants being
able to out compete weeds and earlier succession plant species.
When mycorrhizal colonization is low, or less than the desired range,
given that the desired plant requires VAM or ectomycorrhizal colonization
or ericoid mycorrhizal fungi, then check how low the colonization is.
If less than perhaps 10% — 15%, then addition of mycorrhizal spores
would be a good idea. If it is an annual plant, placing VAM spores near
or on the seed or seed pieces is the simplest way to get the roots colonized
as soon as the roots area produced.
With permanent turf, adding VAM spores into the compost mixed into
the aeration cores gets the VAM spores into the root system without
destroying the turf.
With perennial plants, verti-mulching and adding the VAM or ecto-
spores into the compost mixed in the vertimulch is the simplest way
to get the spores next to the root system. In cases where we have added
inoculum in this fashion, roots have gone from 0% colonization to 25%
— 30% within 1 year, and to 50% — 60% in 2 years, with addition
of humic acids through the season to help the mycorrhizal fungi grow
If colonization is between 15% — 40%, then all that is needed is
additional fungal foods to help the mycorrhizal fungi improve plant growth,
reduce plant stress, and improve root protection.
There is a dose response relationship to humic acids additions. Typically
addition of 2 — 4 pounds of dry product, or 1 — 2 gallons of liquid
product per acre are adequate to improve fungal growth. But, if there
are toxic chemical residues to overcome, additional humics of fulvics
may be needed. It is best to check periodically to see that colonization
is improving as desired.
Be aware that that most humic acid products contain 10% — 12% humic
acids. If the product you are considering is less expensive, please
check the concentration of humic acid. Half the concentration of the
humic acid means they can drop the price, but your fungi get less benefit.
Check colonization periodically to make sure the fungi are growing
and colonization is increasing. Weather can cause problems with colonization,
and severe drought, floods, burns, compaction causing by over-grazing,
heavy machinery, herds of people walking on the lawns or turf can reduce
colonization. If that happens, additional applications of fungal foods
will be needed to help resuscitate the damage.
Fungi are just like
any other organism. If they are harmed, they need care to recover.
Triage for fungi includes adding foods they love (humic acid is like
chocolate to a choc-a-holic, but they’ll also accept any woody,
wide C:N ratio fungal food), and putting on a mulch or litter layer
on the soil surface.
If colonization is above 40%, then the plants are getting the help
they need from the fungi. Periodically check to make sure nothing has
What if colonization seems too high? This is extremely rare, but does
happen, and seems to be associated with the fungi taking more than their
fair share of the plant’s resources. Stop applying fungal foods.
Consider helping the bacteria compete with the fungi for a bit.
Read also: Flagellates, Amoebae, Ciliates