Saturday, July 20, 2013

Soil Science

Now for a three part digression back to Science World. 

When I was at Dancing Rabbit, I discovered that they had a pretty good library.  I spent quite a bit of time there reading various books.  One thing they had a lot of were books on soil science.  (Which make a lot of sense since many people there were into growing food.)

As I was looking through the books, I realized that a lot of the things I'm interested in (composting--see my post Thinking in Circles, 1/6/13, humanure--see Humanure, 1/10/13, and growing food--see Gardening as Social Change, 5/7/10) were related to soil and that soil science was a very complex discipline involving the sciences of geology, botany, microbiology, ecology, and a lot of chemistry. (I will write more about chemistry in my next post.)   I've also written about extensively about soil and my interest in it before--see Food (Soil and Seeds), 5/13/09, and especially The Story of Soil, 3/13/10.  This post will be a recap of a lot of that.

Soil science begins with rock. Due to water and wind the rock is broken down or weathered.  The fractured rock becomes boulders, stones, cobble, and gravel.  This collection of loose mineral material is called 'regolith'.  This is the 'parent material' from which soil is born.

As even the gravel is pulverized, it's broken into the grains which become soil: sand, silt, and clay, each finer than the one before.  A soil of mostly clay won't drain water very well, a soil of mostly sand won't hold water and drains too quickly.  Loam, the best soil for growing things is 40% sand, 40% silt, and 20% clay.  (A little clay goes a long way.)

The most important element in the soil, both to hold water and for plant growth, is the organic matter, also known as humus.  This is the endpoint of things like compost and humanure.

About half of typical soil is solid material (sand, silt, clay, and humus) and half is air and water, which is also very important to the health of plants, since roots need to breath and take in water.  Pores in the soil (the spaces between soil particles) is where the water and air reside.

"Good structure allows the soil to retain adequate water as well as drain excess water; promotes ease of seedling emergence, root penetration, and tuber growth; air movement; and erosion control."  (from Eash, Green, Razvi, and Bennett, Soil Science Simplified, Fifth Edition--this is a good reference book on soil science that I got out of the public library and have been reading since I got back from Dancing Rabbit. It's not one of the books I read while I was there.)

There are also a lot of creatures that live in the soil, ranging from microorganisms such as bacteria, actinomycetes, algae, fungi, mycorrhizae (fungi that live in or around the roots of plants and provide nutrients and water for the plants), protozoa, and nematodes,  (a really good book about all of this is Teaming with Microbes by Jeff Lowenfels and Wayne Lewis, a book I did read while I was at Dancing Rabbit) to larger organisms such as earthworms, springtails, mites, pill bugs, sow bugs, ants, and even larger animals like mice, shrews, rabbits, and moles.

There's a lot more I'm learning about soil chemistry (see my next post), erosion, and types of soil, but this is the basics.  If we are going to focus on the needs of people (which I think any radical social change is going to need to do), we have to realize that plants provide our food and air and basically keep us alive.  Soil is what keeps plants alive.

Quote of the Day:  "The soil is the lifeblood of your land and, therefore, you." - Nicole Faires

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