Chris Hogg wrote:
On Sat, 15 Mar 2008 17:53:24 GMT, Stuart Noble
wrote:

Chris Hogg wrote:
On Fri, 14 Mar 2008 17:38:48 -0000, "Donwill" popple @diddle .dot
wrote:

In acid soil and peat what are the acids that make it so?
Carbonic? a bit weak perhaps?
Nitric?
Wouldn't be Sulphuric.
Can't believe it would be Hydrochloric.
Any ideas, and where would it come from.
Don

The commonest soil acids are humic acid and fulvic acid. These are
organic acids with very complex structures, unlike some of the more
familiar organic acids such as acetic acid (vinegar) or fatty acids
such as cooking oils. They derive from decaying vegetable matter. Soil
scientists have studied them for years to try and understand their
structures, but AFAIK haven't come up with definitive results yet,
simply because the structures are so complex.

Humic acid can be extracted from peat, for example, by stirring it in
water with a few spoonfuls of baking soda to make it alkaline, and
letting it stand for a few days. Drain off the brown water that
results and add some vinegar or other acid to neutralise any remaining
baking soda, and a voluminous yellow-brown jelly-like mass will form.
This is 'pure' humic acid.

See also http://en.wikipedia.org/wiki/Humic_acid
and http://www.thekrib.com/Chemistry/humic.html

Humic acid was on sale at my local garden centre as a "soil
conditioner". Looks like coal dust and appears to be insoluble in water.
I read somewhere that it occurs naturally above coal deposits in parts
of the U.S. and Australia.

Lignite (soft coal, brown coal) is often rich in humic acids and is
sometimes processed commercially to extract the alkali-soluble
components in a manner much as I described above. The products are
used as protective colloids and dispersants for clays in a variety of
applications. There's a lot of lignite associated with ball clay
deposits in South Devon, but AFAIK it's not processed to extract the
humic acids. Kassel, in Germany, was at one time a well-known source
of lignite extracts.

But I doubt that what you've seen is the extracted material. Most
probably it's the lignite itself. Whether it has any beneficial
effects on soil in that form, I don't know, but I would guess it would
take years to break down and release the humic acids onto the mineral
particles in the soil, which is where it's needed. After all, the
lignite in South Devon has been in the ground for some 20 million
years, and has become pretty stable and inert over that time.


Yes, I did wonder about that. I guess the purveyors of humic acid are
banking on an alkaline soil. There seems to be a lot of controversy over
whether potassium or ammonium humates are beneficial.
Interesting that Kassel Brown is a recognised dye in the art world.