EXPERIMENT 8

WATER-HOLDING CAPACITY OF SOILS

THINGS YOU NEED: Equipment from Experiment 7 (except for pebbles, gravel, and sand). Some soil samples

Nature took thousands of years to form the thick layer of soil on which we grow food. But pollution and erosion could destroy that soil in only a few years. And where would that leave us?

In his book Cry the Beloved Country, novelist Alan Paton said of soil, “Keep it, guard it, care for it, for it keeps man, guards man, cares for man. Destroy it and man is destroyed.”

Erosion is the wearing away of soil. To a large extent it depends on how much water different soils hold. Soils with a high water-holding capacity take in a lot of water when it
rains and let it go slowly. This is good in two ways: It reduces water runoff, which means less erosion and less severe flooding. And it increases water seepage into the ground, which builds up our ground water supply, an important source of water.