Elaine,
Quite often, mycorrhizal inoculum manufacturers have
formulated their inoculum ingredients to work efficiently with the spores,
hyphae, and host plant root fragments containing spores and hyphae. When
those ingredients are mixed into the tea, you lose the biological design of the
manufacturer. Making probe holes about 10 inches into the soil around the
plants and putting about a teaspoon of inoculum down each hole and then pushing
the soil in at the top of the hole will work quite well. (Depending upon
the manufacturer... some may require more inoculum because they have a low spore
count.) Where to place the holes has to be thought out too. If a
plant was recently planted, poking holes in the ground a couple feet or more
away from the plant probably isn't going to be any where near the plant's
roots. For most AM fungi, the hyphae are more infectious than the
spores.
Also, if you mix mycorrhizal inoculum into your tea, there
needs to be constant agitation or the spores can settle or float to the top and
you will have serious application problems. With the inoculum mixed into
tea there is also the problem of trying to figure out how much to apply.
For well established plants like trees, a set of holes out at
the drip line about 10 inches deep and a foot apart will work fine. I like
to get in close to the trunk 2-3 feet and put another set of holes in the soil
so the mycorrhizal fungi can grow out from the plant as well as get into the
feeder roots out around the drip line.
I've found that for well established grapes and roses, six
probe holes into the soil close the plants (about 3 inches from the trunk of the
plant) works quite well.
If a tree is surrounded by turf grass, do a core aeration and
mix the inoculum with carrier material (sand or trace minerals) and use a drop
spreader to apply the inoculum. Then water the area down well. Most
grasses will colonize to about 50% and the roots are mingled with the tree
roots. The AM fungi will vector over from the grass roots onto the tree
roots. Cover crops in between grape vines (if they are mycorrhizal) can
make very nice vectoring agents for getting the mycorrhizal fungi onto the
underlying grape roots.
The reason we want the inoculum on or as close to the plant
roots as possible is that there is a substance called (flavonoids,
flavonols, flavonone) which is part of the exudate coming out of the roots
which serves as a trigger to cause the AMF spores to germinate or the AMF hyphae
to start growing. In some cases, a combination of carbon dioxide and
flavonols are the triggering agents, in other cases, only
the flavonols are the triggering agents. There is a company in
the Midwest that now makes a flavonol product which can be mixed with water and
then put down as a soil drench and will cause a much higher colonization rate
with the AM fungi. That product can not be mixed with tea because the
bacteria will eat it all up. It also can't be put into the inoculum or it
will cause the spores to germinate in the inoculum or the hyphae to start
growing. Once the spores germinate or the hyphae start growing they have a
rather short time to work their way into the roots of a plant. It's the
plant that feeds the AM fungi and if it doesn't get hooked up fairly promptly
the fungi will expend it's food and die. This is why we want it near the
roots of the plant. Probe holes work slick when you can get in among a
bunch of roots. If you take the cover crop treatment approach, those
plants can easily be treated and the AMF will be sustained nicely and
transferred over to the plant roots you are trying to inoculate.
There is another bugaboo to be aware of... well three
actually... one has to do with phosphorous. If a plant has taken up
a lot of phosphorous, then colonization by the AM fungi can be totally inhibited
to none at all or a very low value. I think this has something to do with
a reduction of the flavonols in the root exudates. (This is just my
hunch.) I have to do some searching to see if there are any definitive
research abstracts available to verify my hunch. I'm thinking my hunch is
true because of no to low colonization rates. That would be expected if a
lot of phosphorous presence in the plant would somehow suppress the flavonol
production.
The second bugaboo... once the AM fungi is well colonized in a
plants root system, if a lot of free phosphorous is made available to that
system, the flow of nutrients through the hyphae of the mycorrhizae will shut
down and many of the leaves will turn yellow. In a severe case, the plant
leaves and stems, etc., will dry up and you can lose the plant... like a reverse
osmosis. If you make a tea that has a lot of free phosphorous present,
this situation can damage plants that are well colonized with AM fungi.
Bird manures can be the source of a lot of free phosphorous. I first
experienced this situation when I put some Alaska Fish Pellets around a couple
of rows of Raspberry plants. The NPK was 8-5-1. The leaves of the
plants yellowed up from the ground about 3 feet. A few of the well
colonized plants dried up and were lost. I scraped the fish pellets away
and watered the plants well and they all recovered except the ones that dried
up.
And a third bugaboo.... this probably won't affect people who
use compost teas. Strange as it may seem one can work with a grower and AM
fungi has been applied and CT is being used and don't be too shocked to find the
grower applying some sort of systemic fungicide to his plants as a precautionary
measure... even after you have spent all kinds of time educating the grower
about what to do and what not to do. You just can't predict what people
are going to do. Well, certain fungicides are super effective at killing
AM fungi and you will have to start all over from the beginning with another
application. Surprisingly, some fungicides at low levels are actually
stimulating to AM fungi.
Just a few tips to consider..
--Thomas Giannou
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