Agriculture Reference
In-Depth Information
Top quality humate sources will have a humic acid content above 70% by weight
and an exchange capacity of 200-300 meq.Application rate varies depending on
soil type, but in low CEC soils around 400 lbs/ac or 400 kg/ha annually would be
our recommended maximum application.
Charcoal or Biochar (Terra Preta Soils)
Charcoal made from plant matter, more or less finely ground or powdered, and
intended as a soil amendment, is also called biochar. Charcoal or biochar has one
of the highest exchange capacities of any known material.
One of Biochar's secret assets lies in its large surface area of
approximately 500 m2 per gram! This is as a result of the micropores
formed during pyrolysis. In general the higher the pyrolitic temperature the
larger the surface area of the finished material until it reaches a
temperature at which deformation occurs. It is this large surface area that
provides a vast protective habitat for beneficial bacteria and fungi in soils
where it is applied; a sort of coral reef for Fungi and Bacteria.
Another important attribute is the Cation Exchange Capacity (CEC) of
Biochar. CEC is a measure of the surface charge in a soil or a Biochar and
in basic terms it is the ability of a soil/Biochar to hold onto nutrients. The
benefits for soil work both ways as it will absorb
[sic]
nutrients and prevent
leaching yet release the nutrients when required.
Researchers have measured the CEC of “fresh” biochar made from pine
sawdust pellets and pine timber ranging from 22meq to 138meq. (
Characterization
and Comparison of Biochar, Herbert et al, CalPoly2012).
It is also known that as biochar
ages its exchange capacity can increase, up to an order of magnitude (10x).
In 2006 researchers compared several ancient char-amended soils (terra preta
androsols) in the centralAmazon with adjacent soils to which char had not been
added. The most impressive result was an androsol with an Effective CEC of
213meq compared to adjacent soil with an ECEC of 23meq. This same androsol,
estimated to be 600 to 1000 years old, tested as containing 9064ppm Phosphorus
and 17 545ppm Calcium, vs the adjacent soil with only 273ppm P and 115ppm Ca.
(Black Carbon Increases CEC in Soils, B Liang et al, Soil Sci. Soc.Am. J. 70:1719-1730, 2006)
The advantages of using biochar to increase exchange capacity include:
Unlike organic matter and humus, which can quickly decompose,
especially in warm climates, biochar is stable for centuries or millennia.
Unlike humate ores, biochar can be used in large amounts.
Biochar can be made from free or inexpensive local waste materials and
produced nearby or on site.
The potential disadvantages of biochar are generally short-term:
