Earthworms

There are a lot of worms in the soil.
If we put together all the worms living in a hectare of soil (in a football field), they would make a big heap and would weigh as much as two oxen.
Worms eat the remains of plants that are mixed with the earth.
Worms also eat a lot of earth.
You often see on the surface of the soil the little heaps of earth that worms have left.
Worms make a lot of holes in the soil.
Worms improve the soil structure.
By making holes and by eating earth, worms mix humus, sand, silt and clay. They work the soil like the farmer with his hoe.
So worms are very useful in the soil.

Rats and other animals

Rats, rabbits and lots of other animals dig big holes.
These animals eat roots, young stems and leaves.
They are not useful.

Termites

Termites destroy dead plants.
They make holes in dead plants.
For instance, they destroy wood.
Part of the organic matter remains on the spot, mixes with the soil and produces humus.
The rest is taken away by the termites to their nests.
Termites bring up fine earth.
They go deep into the soil to get fine earth.
They bring it up to make their nests.
When a nest is destroyed, the fine earth is mixed with the cultivated layer. This layer becomes deeper.
But termite nests are sometimes very big and very hard. They are a nuisance to the farmer.

Other insects

In the soil there are also many other insects such as ants and caterpillars.
These insects disturb the soil as worms do and decompose organic matter.
Certain insects eat leaves or roots and kill the plants.
Insects, both good and bad, change the soil.

Microbes

We saw that there are very many microbes in the soil.
Some microbes change organic matter into humus.
Other microbes bring nitrogen to plants.
We know that leaves get carbon from the air (see Booklet No. 2, page 21).
There is also nitrogen in the air. To grow, plants need nitrogen. But leaves cannot take nitrogen from the air.
In the soil there are microbes that can take the nitrogen in the air for their own food.
When these microbes die, they remain in the soil and decompose.
The microbes' nitrogen is changed into mineral salts.
The roots of plants can absorb these mineral salts through their root hairs (see Booklet No. 1).
Everywhere in the soil there are microbes that Can take in nitrogen.
Some of them gather on plant roots where they form little beads, or nodules.
The microbes in these little beads bring nitrogen to the plants.
Not all plants have these little beads.
They are found only on plants of the legume family.
Groundnuts, Dolichos bean, Crotalaria, beans, peas, Stylosanthes are all legumes.

Groundnut plant