permaculture

["Lawrence F. London, Jr." <venaurafarm@bellsouth.net>]

-------- Original Message --------
Subject: Re: [SANET-MG] Soil solution concentrations of phosphorus
Date: Wed, 29 Dec 2010 13:08:10 -0500
From: Beginning Farmers <beginningfarmers@GMAIL.COM>
To: SANET-MG@LISTS.IFAS.UFL.EDU

Speaking of microorganisms and phosphorus...

In the late 1980's researchers at Michigan State did a simple experiment
with white clover grown in the presence of mycorrhizae (which is extremely
important in phosphorus uptake by plants). In the experiment they used some
soil that was phosphorus deficient, and some that had plenty of available P.
What they found was that the P deficient plants were colonized by the
mycorrhizae at much higher levels than the plants that had plenty of
phosphorus.

A curious result. But that's not where the story ends. Based on this result
it was postulated that the plants were actually sending out a 'signal' when
they were under P stress that 'told' the mycorrhizae 'we need help'. Another
researcher, Muralee Nair, was able to isolate a compound called formononetin
- an isoflavanoid (think soybeans) that was responsible for the signal.
Formononetin was present in such small quantities that Nair didn't believe
the results at first. But after isolating and synthesizing the compound, he
consistently got significant increases in not only mycorrhizal colonization
but also rhizobial nodulation (associated with nitrogen fixation) in
legumes. You can get the paper for free here:
http://onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.1991.tb00568.x/abstract

When I was working with them testing the product, we were able to get
significant increases in plant growth and production by applying
formononetin at levels as low as 30 grams (yes, grams) per acre! I tested
this product on plants all over the country with mixed yield results (I
never saw significant decreases, but sometimes didn't get increases) - which
I attribute to the fact that conventional farmers typically apply so much
phosphorus that increased mycorrhizal colonization doesn't always result in
increased yield.

Just another example of the beautiful complexity of nature, the wonders of
symbiotic convolution, and the importance of healthy living soils for
optimal plant growth.