Mycorrhiza tolerance for fertilizer levels

K N and P J Harris ecoli at
Wed Dec 4 15:01:26 EST 1996

> ==========
> bionet/plants #2860, from don at, 1306 chars, Tue  26 
Nov 1996 09:45:09 +0
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> Article: 11433 of bionet.plants
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> From: don at
> Newsgroups: bionet.plants
> Subject: Mycorrhiza tolerance for fertilizer levels
> Date: Tue, 26 Nov 1996 09:45:09 +0000
> Organization: Internet Access of Ventura County 805.383.3500
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> It has been well documented that excess levels of nutrients - luxury
> levels - harm the mycorrhizal association with plants, in effect 
> the plants dependent on just their own root systems.  However, we are
> finding significant differences in opinion as to where the
> excess-nutrient dividing line occurs, especially for phosphorus
> amounts.  Does anyone know of good research on this topic, so that we
> might better advise our mycorrhizae inoculum customers who wish to
> convert to more biological growing methods?  Thanks in advance, Don
> Chapman, Bio/Organics, Camarillo CA
Hello Don,
The problem is mainly one of phosphorus obviously. The real problem in 
terms of defining a "cut-off" level is in the methods available for 
assessing "available" phosphate.Various extractants can be used and they 
tend to give variable results with different soils. The (probably) most 
wisely used is the "Olsen P" method but even then it is only useful on a 
comparative rather than absolute basis. The one we favour is an "anion 
exchange resin in a bag" method but it is tedious. I will copy your 
letter to my work address and see if I can find a few refs for you.
Peter Harris,
Reading University, Soil Science dept. UK.

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