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Soil formation

Feldspar weathers into clayThe beginning of Life in the Soil covers the abiotic (non-living) elements that create soil, generally at a rate of about an inch every 500 to 1,000  years.  The type of soil that will be formed in an area is influenced by the type of rocks involved, the topography of the site, climate, time, and living organisms.  Of these elements, the one I found most fascinating involved the chemical reactions that occur in rocks to create soil.

For example, I hadn't realized that clay and sand both have specific chemical formulas and are created when feldspar (an abundant mineral in many rocks) reacts with carbonic acid (formed from water and carbon dioxide).  All feldspars contain aluminum, oxygen, and silicon, and each also has one of the following constituents: potassium, calcium, sodium, and Soil horizonsbarium.  When carbonic acid (H2CO3) and potassium-based feldspar (2K(AlSi3O8)) react and spit out clay (Al2Si2O5(OH)4) and sand (4SiO2), potassium carbonate is also formed.  Perhaps this is why old soils are often excessively high in potassium?

Another fascinating tidbit pertains to soil horizons.  If you've done any reading about soil, you probably know that natural soils have a layer of partially-decomposed plant matter (the O layer), beneath which is rich top soil (the A layer), then a small, pale E layer out of which the organic matter, clay, and nutrients have leached, followed by a slightly darker B layer.  Nardi explained that the textbook scenario is really only seen clearly in coniferous forests, where toxic levels of iron and aluminum build up in the B layer and keep most roots and soil life out.  In deciduous forests, in contrast, living things tend to mix the layers up, especially if earthworms have been introduced.

Stay tuned for more on the soil "mixers" in tomorrow's post.  In the meantime, you might want to check out my ebook for tips on taking a soil sample and learning more about your soil texture.

This post is part of our Life in the Soil lunchtime series.  Read all of the entries:

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Anna, I enjoy your nerdier posts. One of the more interesting things I learned is how the rain/CO2/geological weathering story might be fundamentally dominated today by plants. See lengthy scientific paper: I wonder how much soil profiles differ because coniferous forests are worse at geological weathering?
Comment by Brian Wed Jan 8 10:54:30 2014

Brian --- I'm glad to hear you like the nerdier posts --- I sometimes wonder if anyone reads those. :-)

Your link didn't work for me, though --- I think I didn't have the right permissions. Do you mind sharing the authors and title so I can look it up?

Comment by anna Wed Jan 8 12:23:51 2014

One very unique homestead, $1,500 per acre, the opportunity of a lifetime