What humus does

· Humus makes soils richer.

From the soil the plant gets mineral salts (see Booklet No. 1, page 19).
The leaves turn the raw sap into elaborated sap (see Booklet No. 2, page 20).
The plant feeds on elaborated sap.
Wood and leaves are organic matter rich in mineral salts and carbon.
Organic matter rots and makes humus.
Humus returns to the soil the mineral salts used by the plant.

Humus returns the mineral salts to plant

Humus improves soils

Heaps of bricks, cement and sheet iron do not make a house.
To make a house they must be arranged, must be joined together.
Sand, clay, silt and pebbles without humus do not make a good soil.
They must be arranged, must be joined together to make a good soil.
The way in which sand, clay, silt and pebbles are joined together is called the soil structure.
It is the humus which joins together sand, clay, silt and pebbles.
Humus is necessary for soil structure.

Bad soil structure

This structure is bad because there is no humus.
The sand, clay and silt are not joined together.
Air and water circulate badly.
Roots penetrate badly, breathe badly and feed badly.
This is a bad soil structure.

Good soil structure

The structure is good, because the sand, clay- and silt are joined together by a mixture of clay and humus.
Air and water circulate well.
Roots penetrate well, breathe well and feed well.

Good soil structure

· Humus improves sandy soils.

Sandy soils with humus hold water better.
They are less easily carried away by wind and rain.

· Humus improves clay soils.

Clay soils with humus are less hard.
Air and water circulate better.
Soil without humus is not good soil.