From: "Lawrence F. London, Jr." <venaurafarm@bellsouth.net>
To: permaculture <permaculture@lists.ibiblio.org>
Subject: [permaculture] Fwd: [SANET-MG] Fertilizer effects on microorganisms and terroir
Date: Sun, 12 Dec 2010 20:26:11 -0500
-------- Original Message --------
Subject: [SANET-MG] Fertilizer effects on microorganisms and terroir
Date: Sun, 12 Dec 2010 20:15:29 -0500
From: Joel Gruver <jgruv@HOTMAIL.COM>
To: SANET-MG@LISTS.IFAS.UFL.EDU
Hello folks,
I have been too busy wrapping up the semester to give most recent SANET
posts more than a cursory glance... that said, as a soils person I feel
compelled to quickly comment on several recent topics of discussion.
fertilizer effects on soil microorganisms have been intensively
investigated...
some studies have looked at short term effects while others have looked
at longer term effects... some studies have evaluated effects on
specific microbially mediated processes while others have looked at
changes in microbial abundance and diversity.
The effects of specific fertilizer treatments on specific microbial
parameters vary widely depending on context... soil properties (e.g.,
pH, CEC, clay content, OM content), weather, season, cropping system,
duration of the experiment....
When considering such a diffuse cloud of evidence, I try to step back
and consider the broader ecological context.
The application of fertilizers (or any other type of agronomic input)
can be viewed as an ecological disturbance. Ecological responses to
disturbance depend on both ecosystem and disturbance
characteristics...the magnitude of the disturbance, the frequency of the
disturbance, opportunity for recovery between disturbances, specific
disturbance modes of action, and ecosystem resilience...
Fertilizers have a number of different modes of action through which
they "disturb" microbial communities.
nutritional effects
Both bacteria and fungi can directly utilize inorganic ions and organic
molecules so inorganic fertilizers can directly stimulate microbial
growth if the particular nutrients supplied by the fertilizers were
limiting. Responsive species may gain competitive advantage over less
responsive species. Nutritional effects on plant growth can have a
cascade of effects on the whole soil food web.
salt/osmotic effects
fertilizers vary in their saltiness or tendency to create osmotic stress
(quantified as the salt index of a fertilizer).
Method of application (banding vs. broadcast) and soil properties
(moisture content, texture, CEC, OM) have a big impact on the osmotic
stress created by a fertilizer...
direct toxicity
some fertilizer materials like anhydrous ammonia are directly toxic and
sterilize the zone of application
low levels of contaminants in fertilizers (e.g.,
heavy metals) can have toxic effects after many applications
affects on pH
many N fertilizers are acidifying... if the acidity is not balanced by
liming, the long-term effect can be quite suppressive of microbial activity
more subtle physiological effects
specific metabolic/enzymatic pathways are stimulated or suppressed
depending on the forms and concentrations of ions to which
microorganisms are exposed
effects on soil physical properties
fertilizers that add sodium can cause dispersion of soil structure... in
contrast materials like gypsum that add calcium and increase the ionic
strength of the soil solution can promote flocculation.
Bottom line… IMHO it is not possible to provide a meaningful rule of
thumb such as 100 lbs of *fertilizer*
per acre is harmful to soil microorganisms.
“Recreate the mineral profile of the North Central US
prairies on the prairies of the Willamette Valley of Oregon and the
nutritional content of the forage changes to that of the forage grown on
the North Central prairies. It works; I can post the soil and forage
tests to prove it, and the health records of the animals raised on that
land as well.”
Michael A, I would very much like to see your data showing
the effects of specific remineralization programs on the mineral content
of crops.
I am pretty skeptical that fertilizing top soil (i.e, the plow
layer) with specific minerals can recreate the effect that a full soil
profile has on crops in areas with exceptional terroir... but I would
love to hear about attempts to accomplish this.
I don’t know if you happened to take a look at the link I
provided a few weeks back for a presentation on soil testing… (I can
post another link if you are interested) but one of the key points was
the soil testing doesn’t tell you about most of what controls nutrient
uptake during a growing season…e.g., moisture, temperature, microbial
activity, rooting depth, root health…
I tell my students that soil testing is kind of like a 40 yard dash
time… it is a useful indicator but is far from the only thing a coach
needs to know to predict whether a prospect is likely to be a star player.
Soil is a black box that does many interesting things to applied
minerals… crop uptake is far from a guarantee.
Many factors affect the nutrient content of crops…
are you familiar with this report?
"Still No Free Lunch: Nutrient
levels in U.S. food supply eroded by pursuit of high yields"