What's Hiding in the Dirt?
Grab a handful of dirt from outside. It looks plain and brown. But in just one spoonful of healthy dirt, there can be MORE living things than there are people on the entire planet! Tiny bugs, worms, and even things too small to see are all working down there.
What You'll Learn
- What soil is made of - Why worms are soil's best helpers - How plants use soil to grow - Why we call soil "alive"
Soil Is Not Just Dirt
Soil is made of tiny bits of broken rock, old dead leaves, water, air, and living things. Scientists call the broken-down leaves and plants "humus" (say it: HYOO-mus). Humus is like food for your soil. Dark, crumbly soil usually has lots of humus, and that means it's great for growing plants.
Squeeze a handful of soil. If it's dark, smells earthy, and holds its shape a little, it's full of humus and ready to grow things!
Earthworms: The Underground Diggers
An earthworm has no eyes, no legs, and no lungs — but it can dig tunnels all day long. As it eats through soil, it leaves behind tiny droppings called castings. Castings are packed with nutrients, so worm tunnels are actually feeding the plants above them! One acre of good farmland can hold over a million earthworms.
Why are earthworm tunnels helpful to plants?
Three Layers of Soil
If you could slice into the ground like a cake, you'd see layers called horizons. The top layer, topsoil, is dark and full of life — this is where seeds sprout. Below that is subsoil, which has less humus but more minerals. At the very bottom is bedrock, solid rock that soil hasn't broken down yet.
Match each soil layer to its description.
Terms
Definitions
Drag terms onto their definitions, or click a term then click a definition to match.
Why Farmers Protect Their Soil
It can take over 500 years for nature to build just one inch of new topsoil. That's why farmers plant cover crops and rotate what they grow — so wind and rain don't wash the good soil away. Soil isn't something we can quickly make more of, so taking care of it matters.
Soil scientists are called pedologists. Some of them can identify a soil type just by rubbing it between their fingers!
About how long does it take nature to form one inch of new topsoil?
Build a Soil Jar
Fill a clear jar halfway with soil from outside, then add water until the jar is nearly full. Put the lid on, shake it hard for 30 seconds, then set it down and don't touch it for a day. Draw what you see: the layers should settle with heavier sand at the bottom, silt in the middle, and floating bits of humus on top. Label your drawing with the three layers.
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