agroforestry question

truffler1635 at my-deja.com truffler1635 at my-deja.com
Tue Jan 18 11:20:41 EST 2000


In article <3883C867.3C13486C at michweb.net>,
  DVK <dvank at michweb.net> wrote:
>
>
> TREEFARMER at webtv.net wrote:
>
> > Regarding Joe's post on evapotranspiration causing yield loss.
> > Previously this idea was one I also subscribed to along with fertilizer
> > loss and shading. It was only after many hours of study of the forest
> > edges on our farm that I became convinced that the excess of moisture
> > caused the yield loss.
> > It seems we can have good yields next to timber if there is clear sky
> > directly above the plants and the canopy density of the adjacent timber
> > isn't dense. Maples and Osage Orange aren't good, Black or Honey Locust
> > is ok.
>
This discussion sounds like the problem is more one of mycorrhizal
fungi, or lack thereof.
> Doesn't the Locust also fix nitrogren into the soil (as would a legume)?
Locust is a legume which is considered nitrogen-fixing. However, new
research suggests it is not the legume itself that fixes nitrogen, but
rather a bacteria, usually associated with mycorrhizal fungi, which
cause the nitrogen fixation. At Oregon State University 3 years ago,
various common hypogeous fungi (truffles) were tested for their
association with this nitrogen-fixing bacteria. All four (Hymenogaster
parksii, Barssia oregonensis, Rhizopogon vinicolor and Tuber gibbosum)
were found to be associated with the bacteria. In addition, the root-
structures found associated with the bacteria are combinations of plant
and fungi.
> Yet another variable to consider.
>
> > Unfortunately moisture damage early in the crop's life, basically ruins
> > its chances for any yield later regardless of the weather or human
> > intervention. It's like once a runt always a runt.
Plant life without appropriate mycorrhizal fungi produce the same sort
of plants. While a seedling _may_ continue to grow, it seldom produces
seed.

As for fertilizing, to preserve mycorrhizal fungi it is best to use
little or no fertilizer. The fungi apparently act as micro-fertilizer
plants to begin with. But many mycorrhizal fungi are obligate. While the
fungi are beneficial as nutrient gatherers, the host plant can also
disassociate with the fungi if it nutritient needs are met, such as
providing it with fertilizer.

In addition, there may need to be a succession of mycorrhizal fungi as
individual plants mature. It was recently found that a since half-
centimeter of rootlet can host 7 different species of mycorrhizal fungi.
There are potentially many such sites on most plants.
> > Since we don't grow rice here I can't speak of that crop, only corn and
> > beans.
Both corn and beans (and 95% of all other plant life) needs mycorrhizal
fungi for survival. There are some soils where the Glomus species
necessary for corn survival is not present. (Glomus are among the most
primitive of mycorrhizal fungi, very similar to the Glomites found in
Devonian shale.) Corn in these soils sprouts, grows for perhaps 2-3
weeks, then dies.

Most other legumes (clover, vetch, soybeans, beans, etc) are so
dependent upon these mycorrhizal fungi and bacteria that they are pre-
inoculated by seed companies (coated to the seed) before planting.

It is my _belief_ that in nature, some insect species may the vectors
for doing exactly the same thing. Consider: various Nitulid beetles
consume Rhizopogon truffles. Some of these beetles are so specific that
individual beetle species have been reported only on specific Rhizopogon
species. While harvesting Rhizopogon, Barssia, Tuber, Hymenogaster,
Melanogaster and other truffle species, I have found some of these
beetles. I believe I have also seen them inside Douglas fir cones. They
appear to eat around the seed, allowing it to fall out of the cone
easier. It is possible that Rhizopogon spores adhere to the beetles and
are carried about with them, are transferred to seeds via feces or
physical contact, and thus are pre-inoculating tree seeds before they
fall from a cone. Keep in mind that an _average_ sized Rhizopogon of
2.5-5cm diameter may contain a billion spores. (The average sized
Agaricus bisoporus, by comparison, produces merely 25 million spores or
so.)

Daniel B. Wheeler
www.oregonwhitetruffles.com


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