What is Soil?

Did you know that nearly all the soil that exist in the world today was once rock? Nature has been at work for millions of years weathering and crumbling the rock into the tiny fragments we call soil. This is done many ways. Alternate heat and cold cracks off surface of rock. Wind-blown sand wears away rock. Glaciers scrape rock surfaces. 

Waves beating against a shore pound rocks into smaller and smaller pieces. Certain bacteria give off acids which help crumble rocks. One way to classify soil is composed chiefly of sand. Clay soil has very fine particles and tends to be heavy, cold, and damp. "loam" is a kind of medium mixture of sand and clay.Stony soil contains a large proportion of rocks or pebbles.

"Muck" or peat soil, has few rock particles and is made up chiefly of decayed vegetation. The soil in which plants grow is made up of more than rock particles. It is a complex substance which also contains mineral salt, decayed organic material, and living organisms. The value of a soil depends on its power to supply plants foods, air, and water to the roots of plants. 

If we sterilized soil and killed every living thing in it, the soil would no longer be "fertile". But even if a soil contained all the necessary plant foods, nothing would grow on it without water to dissolve these foods. Water rises in soil just as water rises in a sponge placed in a saucer of water. The rising of this water keeps plants growing even when it does not rain for a long time.