Handbook of Nature-Study · Lesson CCXX · Topic 35: The soil
220. The soil
Goal: Your child can describe soil as rock flour and humus and shows by experiment which soils let water through, hold it, and lift it from below.
You'll need
- Three clear plastic bottles with the bottoms cut off (an adult cuts), cheesecloth or old cloth and rubber bands
- Three cups or jars to stand them in
- Sand, clay and garden loam, about 2 cups each
- Some dark woodland soil from under the leaves
- A watch or timer
- Safety glasses, a small rock and a cloth bag (optional)
- A hand lens (magnifying glass)
- A nature notebook and a pencil (colored pencils if you have them)
What's in the book
The lesson has a leading thought, a method for bringing in and comparing soils, nine observations on how rock becomes soil, and six experiments with hints for the teacher: how water passes through sand, loam and clay, the film of water on each grain, how soil lifts water from below, mulch, acid soil, and treating clay.
The lesson, step by step
When and where
Spring or fall, when the ground isn't frozen. Collect soil from a garden, a sandy spot, a clay bank and under the leaves in the woods. Wash hands after digging.
The leading thought
The soil is composed of rock flour and humus. Soil, to support life, must be porous, so that the roots of the plants may receive through it both water and air.
Feel and look
Rub a little wet soil of each kind between your fingers. Clay feels like putty and can be rolled into a marble; sand falls apart. Look with the lens:
Look at any kind of soil with a lens, and tell why you think it is made up of small pieces of stone and rock.
If you like, make your own "rock flour": put a small soft rock in a cloth bag and pound it with a hammer while wearing safety glasses.
Then look at the dark soil from under the woodland leaves:
Go to the woods, scrape off the leaves and get some of the black earth beneath them. Of what is this soil composed? Is it rock flour? What makes it so black?
Which lets water through? (Experiment 1)
Tie cloth over the necks of the three bottles, turn them neck-down in the cups, and fill one with loam, one with clay and one with sand, the same amount in each. Pour the same amount of water slowly into each and time it.
Which soil takes the water most rapidly? Which lets it through first? Which lets through the most?
Does soil drink from below? (Experiment 3)
Fill the bottles again with dry soil and stand them in a pan with an inch of water.
In which soil does the water rise most rapidly? In which does it rise the highest?
A blanket for the soil (Experiment 4)
Wet two bottles of loam the same. Cover one with an inch of dry, loose soil. Check each day.
Which dries out first?
Today gardeners usually mulch with straw, shredded leaves or wood chips, which do the same job and protect the soil from blowing away.
What we know now
Soil is also alive. A single spoonful of good soil holds millions of tiny living things (bacteria, fungi, mites), besides the worms and insects you can see, and they help turn dead leaves into the dark humus.
Nature notebook
Draw the three bottles and write how long the water took to drip through each. Write which soil would be best for a garden, and why.
Afterwards
Leave Experiments 3 and 4 standing for several days and record what you see each day. The book also has tests for acid soil and for clay; look at them on the page if you are curious.
Tip
The book's Experiment 2, with marbles in a glass of water, shows the thin film of water that clings to every grain of soil. It is quick and easy to add.
Answers to the book's problems
Book's hints: water runs through sand in about a minute, through loam in several minutes, and takes hours to come through clay; sand lets through the most. Water climbs fastest in sand but, given time, climbs highest in clay. The covered (mulched) soil stays moist much longer. Loam, a mix of sand, clay and humus, is best for gardens. Woodland earth is black with humus from rotted leaves.
Worked out for this site from the scan. If a number in your copy differs, trust the book.