[compost_tea] Re: Inclusion of clay in compost

From: Tom Jaszewski <tom_at_livesoil.com>
Date: Mon, 07 Feb 2005 16:45:07 -0000

Anyone have additional information on access to lectures or materials
by Dr. Claude Bourguignon?


http://www.eap.mcgill.ca/MagRack/SF/Fall%2091%20A.htm
Bourguignon pointed out that everyone was concerned about the loss of
organic matter from our soils, but no one was worrying about the loss
of clay. it is just as important if not, more important than organic
matter in providing surfaces for nutrients to bind to.

In the laboratory, Bourguignon complements current soil testing
methods by determining the type and quality of clay present in the
soil. The clay type affects what percentage of the Cation Exchange
Capacity (CEC) is due to the clay. (The CEC is a measurement that
reflects a soils ability to retain cations, in effect a measurement
of the soil's ability to retain certain nutrients). The CEC that on a
soil test is that generated by the levels of organic matter and clay
present in the soil. Depending on the quality of each, the CEC can
also be higher or lower. For example, kaolinites have 30 m3/g (cubic
metres per gram ) of surface on which ions can exchange. Compare this
with montmorillonites , which have almost 30 times as much surface
area and the importance of the clay type in relation to a soil's
nutrient conservation mechanism immediately becomes apparent.
When the CEC based on clay quality has been determined, the CEC in
relation to organic matter can be calculated. Generally speaking, it
will vary 0.5 to 5 CEC for every 1% of organic matter. A good quality
organic matter can mean a 10 fold increase in the CEC of the soil and
consequently its ability to make soil nutrients available.
By stressing the importance of good quality clay and humus,
Bourguignon maintains that it's irrelevant to measure soil nutrient
availability alone, which is what appears in soil test reports. Such
information only gives a picture of the nutrients available at the
time the soil test was taken. It is more important to know whether
the total nutrient content is adequate, and whether the clay-humus
complex and microbial activity is in sufficient health to ensure
mineralization of these soil nutrients. This is why he advocates
measuring total soil N, P, K etc., instead of just available N, P, K
etc.








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Received on Mon Feb 07 2005 - 14:57:46 EST

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