permaculture

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

-------- Original Message --------
Subject: Re: [SANET-MG] Soil phosphate (was organic vrs conventional) - 
chemistry and extraction methods
Date: Wed, 10 Nov 2010 19:24:25 -0500
From: Elaine Ingham <soilfoodweb@AOL.COM>
To: SANET-MG@LISTS.IFAS.UFL.EDU

 Standard soil chemistry reports give information about SOLUBLE phosphate levels in the soil, not the TOTAL phosphorus 
levels.

There are perhaps some 500 different extraction methods listed in soil chemistry books, all of which measure some 
portion of the phosphate in soil solution.  Each extraction method gives you different results, and indeed, the amount 
of organic matter, sand, silt and clay in different soils will influence the ability of any extracting agent to actually 
extract the phosphate present in the soil materials.


Total phosphorus concentrations in soil also can be extracted by different methods, and of course, each method varies 
inn its ability to extract what is actually present.  The stronger the acid, the great the amount of phosphorus 
extracted.  The longer the extraction time, the more extracted.  The more finely ground  the sample to start with, the 
more phosphorus is extracted.  But, many labs sieve out the organic matter bits and pieces before  starting any 
extractions, because organic matter messes up the ease of extraction and causes lots of variability.  I have always 
questioned why that is a realistic thing to do, since I always understood soil organic matter to be part of the soil.

Therefore, the soluble phosphate values given on a chemistry report reflect the extracting agent used.  I use a lab in 
Australia to do my soil chemistry assessments, because they give me data that includes 4 different extraction methods 
for soluble PO4.  I always have to giggle a bit when the values for soluble PO$ range from 0.5 micrograms, to 150 
micrograms, and values in between, all depending on which extraction method was used.

So, which one do you believe?

And then there's the "exchangeable" pool of nutrients, where surfaces of organic matter, sand,silt and clay can exchange 
various cations and anions.  these surface-bound nutrients can easily, in some conditions, become available to plants. 
But, only in certain conditions, so....... as a grower, how useful is it to know about this different set of extractions?

If you do not have any decent set of bacteria, fungi, protozoa, nematodes and / or microarthropods or earthworms in the 
soil, the nutrients in the total "pools"  will not, and cannot, be converted into forms the plant can use .... or 
available forms, or another synonym, ..... soluble.

With decent biology and nutrient cycling going on, the nutrients in not-plant-available forms can be converted rapidly, 
depending on the organisms present, into plant available forms.

So, since pesticides and high levels of inorganic fertilizers kill a large percentage of the life in your soil each time 
these toxic chemicals are used, then pretty soon, the grower will be dependent on inorganic fertilizers to try to get 
the nutrients into the soil in forms the plants can use.  All that is needed to reverse this dependency is addition of 
the right sets of organisms back into the soil.

And the full diversity of organisms are found in compost....... which by definition is an AEROBIC material.  Nothing 
stinky, smelly, black in color or slimy can be called compost.  But so many people in  the scientific world pay no 
attention to whether the stuff they are calling compost is aerobic, and has good biology in it.  Can you see why so many 
papers in the scientific literature contradict each other about whether compost "works" or not?

Just think what happens to N, P, or S, to pH, or toxic materials in organic matter if the material becomes anaerobic. 
No wonder stinky, smelly black stuff can kill plants.  And good aerobic material helps plants grow, as long as the 
proper life is present.


Elaine R. Ingham
President, Soil Foodweb Inc.