Have you ever thought much about soil? If you went on the critter crawl several weekends ago, you might have dug around in soil looking for soil creatures. Did you pay attention to the soil? Soil is a wonderful thing, which deserves further study.
Take your children out to a place they can examine some soil. Start by simply sitting on a patch of soil. Ask your children what they think soil is. Is it alive? (Yes, components of soil are alive.) What does it consist of? Are all soils alike? Smell your patch of soil, what do you smell? Touch the soil. What does it feel like? Is it wet or dry?
If you have time, bring a small bag of sand and a bit of clay with you. Have the children look at the sand, clay and a small sample of your soil. How are they similar? How are they different?
Soil is made up of a lot of different things. The most obvious will be the particles of rocks and minerals. The particles will be of different sizes. Soil scientists name the particles according to their size. The largest particles are sand grains, the middle-sized are called silt and the very finest particles make up clay.
Another important component of the soil is water. As you might guess, water moves through the different-sized particles at different rates. An easy demonstration is to fill three plastic cups, one with dry sand, one with dry potting soil and one with clay. Have the children pour in some water and watch what happens. Older children can time how long the water takes to reach the bottom of the cup with a stopwatch. Usually the water goes through the sand rapidly, and sometimes does not move through densely packed clay at all.
With a group of children, or even children and adults, you can make this even clearer. Tie a bit of blue cloth to one child volunteer, who will represent the water. The rest of children (or children and adults) can be soil particles. First have the soil particles hold out their arms and form a cluster. They are now big sand grains taking up big space. Let the water child try to move through. It should be easy. Then have the soil particles put their hands on their hips and move closer together. Now they are middle-sized silt particles. The water child should still be able to move through, but it will be more difficult. Finally, have the children put their arms tight to their sides and pack together. They are now clay particles. The water child will have a lot of trouble getting through now. If she or he does manage to get in, point out that it is hard to get out again too. Clay holds water tightly once it gets in.
Brainstorm about what else is in soil. Be a soil detective and carefully pick apart a soil sample. You should find some bits of twigs, leaves, plant roots, and other decaying plant parts. This is what is called the organic or humus part. In this case organic does not mean the same as in the grocery store. Organic here means coming from living things, containing carbon.
Another part of soil is air. We often forget that plants need air in the soil as well as water to grow properly.
Did you find any soil critters? Many organisms are found in the soil, such as earthworms, mites, nematodes, fungi and bacteria. They have big roles helping break down the plant matter, adding oxygen to the soil and sometimes increasing the nutrient content, depending on the type.
Time to run out and check out the soil. And when you get back inside, you might want to wash your hands and celebrate by making a dirt cake as a snack. Enjoy!
And if you have time, read some books about life in the soil.
Alvin and Virginia Silverstein have written quite a number of nonfiction and science books. All that we have read have been full of well-researched and interesting information. Life in a Bucket of Soil is another fine example.