Rocket pulls on gloves and scoops potting mix into a bigger pot. "It is just dirt," he says.
Raven hands him a magnifier. "What do you notice up close?"
Rocket squints. "Tiny grains. A bit of old leaf. Little gaps."
Nova hovers beside the pot. "Soil has four main parts," she says. "Two of them you cannot see in a pile."
Rocket frowns and thinks hard.
Soil has four main parts.
Mineral bits: tiny pieces of rock called sand, silt and clay.
Organic matter: bits of once-living things, like old leaves.
Water and air: they fill the gaps between the bits.
About half of most soil is solid bits.
The other half is gaps called pore spaces.
Air, water, roots and tiny living things fill the pore spaces.
Roots need that air and water to grow.
| Part of a healthy soil | About how much (by space) |
|---|---|
| mineral bits (sand, silt, clay) | 45 out of 100 parts |
| organic matter | 5 out of 100 parts |
| water | 25 out of 100 parts |
| air | 25 out of 100 parts |
These numbers are for an ideal soil. Water and air change a lot after rain or dry days.
The mineral bits came from rocks that broke down.
| Statement | True or false? |
|---|---|
| Soil is only tiny rocks. | ? |
| Soil has air in it. | ? |
| Organic matter was once alive. | ? |
| Roots need air and water in the soil. | ? |
Great digging, soil scientist! Tomorrow we sort soil by size with a shake jar.