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Treebeard's Stumper
2 November 2001

Soil Matters

We had a good soaking rain this week in central California, our first in many months! Where does all that water go when it soaks into the ground? It must seep into the pore spaces between the soil particles, but how does the makeup of the soil effect this? Does fine or coarse soil have more pore space, and which holds the most water for growing plants? I've heard it said that cultivating or breaking up the dry crust of soil actually conserves soil moisture better than a solid crust. Can that be? Doesn't breaking up the crust just make it easier for the soil moisture to evaporate?

A worm's eye view of soil? Nah, this is a photo of basalt boulders used to fill a slide area on Boundry Road along the North Umpqua River in Oregon. Those "particles" are really a foot or two across, but they show pore space just as well as a microphotograph. How does the percent pore space of these boulders compare with sand? How would a real microphotograph of soil look different?
Fractals are mathematical objects that are self-similar when magnified. Nature seems to have a fractal quality, as shown in this classic Ansel Adams photograph of Mount Williamson: Clearing Storm. Soil particles also have this fractal quality. Do the physical properties of soil change with the particle size despite the similar appearance?

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Copyright © 2001 by Marc Kummel / mkummel@rain.org