Soil Profile

Soil Profile refers to the layers of soil, in which there are four types, horizon A, B, C and D. Sounds confusing but read on for a simple explanation.

A soil horizon is a specific layer in the soil profile which measures parallel to the soil surface and possesses physical characteristics which differ from the layers above and beneath.

Horizon formation is a function of a range of geological, chemical, and biological processes that occurs over long periods of time. Soils vary in the degree to which horizons are exposed. Relatively new deposits of soil parent material, such as alluvium, sand dunes, or volcanic ash, may have no horizon formation.

As the soil age increases, horizons generally are more easily observed. The exception occurs in some older soils, with few horizons exposed in deeply weathered soils, such as the oxisols in tropical areas with high annual precipitation.

Most important for plant growth are the top two layers Horizon A and B

Horizon A - The Top Soil

Refers to the upper layer of soil which is nearest the surface and is commonly called, top soil containing most of the soil life. In the native bush lands or other areas that haven’t been touched, ploughed or tilled, this layer would include organic litter, such as fallen leaves and twigs. The litter helps prevent erosion, holds moisture, and decays to form a very rich soil known as humus. Horizon A provides plants with nutrients needed for good growth.

Horizon B - Subsoil

The layer below horizon A is horizon B which is sometimes called the subsoil. Litter is not present in horizon B and therefore there is much less humus. Horizon B is were clay and materials washed down for Horizon A are found, some of these elements are here because of the process of leaching. Leaching resembles what happens in a coffee pot as the water drips through the coffee grounds. Leaching may also bring some minerals from Horizon B down to Horizon C.

Horizon C – Big rocks

Comes next as it is below horizon B. Horizon C consists mostly of weatherized big rocks.

Horizon D - Bedrock

This is rock that has been weathered to produce the soil above, unless the soil has been deposited from elsewhere like off flood plains which is soil that has been carried down stream in water then deposited as the flood resides.

Soil is the life blood of your garden so knowing your soil profile will give you a good indication on the health of your soil and the health and success of the produce grown in it. Knowing your soil, will enable you to maximise the quality and yield of your crops.

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Learning what type of soil you have, including what levels of nutrients are in your soil will greatly assist you in improving your soil organically.
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