permaculture

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

-------- 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.

******************************************************************************

Michael Astera wrote:

“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"

http://www.organic-center.org/science.nutri.php?action=view&report_id=115

The average nutrient levels in US produce are not really
much of a standard for comparison.

Do you have data from before and after mineral
application for the produce you mentioned in Maine?

Joel

Joel
Gruver

School of Agriculture
Western Illinois University
(309) 298 1215
j-gruver@wiu.edu