What are rich soils?

‘Rich’ soils are soils that have plenty of the nutrients available that plants need in order to grow. The words ‘good’ or ‘fertile’ are sometimes used instead of ‘rich’ to describe ideal soils. Soils that are poor in nutrients are are called ‘poor’, ‘bad’ or ‘infertile’.

Diagram of soil structure magnified 20 times (from Victorian Department of Primary Industries)
Diagram of soil structure magnified 20 times
(from Victorian Department of Primary Industries)

Soils in tropical areas are usually poor soils, because high rainfall washes away many nutrients. This process of losing nutrients through drainage water is called ‘leaching’ of soils.

The type and quality of the soil in your garden is the key to the health of your plants, and also to how much time you’ll need to spend looking after your garden.

Soil comprises minerals and organic matter. The minerals come from rock broken into very small pieces, and the organic matter arises from both decomposed plant and animal material. The decomposed plant and animal material is called ‘humus’. Water, air and many living organisms are also mixed in with the soil.

To a large extent, the soil in your garden depends upon the type of parent rock it disintegrated from, and the weather during the hundreds or even thousands of years in which it was made.

Soil is always changing. Alterations in physical, chemical and biological properties are happening constantly. Changes arise when we dig and turnover the soil, and due to the plants we add to the garden and remove from it. The work of weather, small organisms and worms also change its properties.

When people talk about ‘soil texture’ they mean the proportion of different sizes of particles in soil. ‘Soil structure’, on the other hand, refers to the arrangement of gaps and fissures between the solid particles in the soil. The number, distribution and layout of these gaps and fissures influences root penetration, its capacity to hold water and to breathe. This porosity comprises up to 50% of the volume of the soil.

 

 

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