- A Little Background
- Where Soil Comes From
- What's in Soil
- Some Specifics
- Loam, Sand, Silt, or Clay?
- Soil Life
- Drainage: Managing Air and Water in the Soil
- Simple Fixes
- Soil Testing
- Balancing Acidity and Alkalinity (pH)
- Nutrient Balance
- When to Improve Your Soil
- Soil Amendments
- Improving Difficult Soil
Excerpt from page 1 & 3
We can understand a lot about how the soil was formed if we can remember just a little junior high school science. Large rocks were - and still are - broken down by the processes of "weathering." This is what our teachers called a "physical" change.
Billions of years ago when the earth had cooled to the point where it had a solid rock crust various kinds of natural forces began to take over. Some of these forces like earthquakes continent-sized glaciers and huge floods were very dramatic in their effect on the landscape. But it was more subtle things like wind, rain, heat, frost, and thawing that did most of the work. You see even the hardest rocks have microscopic pores where water can invade. And there it sometimes freezes.
As the centuries passed water and ice gradually changed the surface of the earth into something different. As Richard Langer puts it in Grow It! "A cupful of water shattered a house-size boulder here a thimbleful of water a six-foot rock there not a million pieces at once but a million pieces in a million years. Glaciers ground the boulders in earth pulverizing pebbles between them as the millstone does wheat. From the stone flour came soil."
Of course it took more than the physical changes of weathering to make the soil what it is today. Our science teachers also taught us about "chemical" changes. The tiny particles of rock that were formed by weathering had to be transformed chemically too. And this was done with the help of soil micro-organisms--plants and animals so small that we need a powerful microscope to see them. The "biomechanical" process that microbes perform continues for as long as the earth exists in its present state.
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