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.