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What is Subsoil?

The definition of subsoil 

Directly beneath the surface soil (topsoil) lies a layer known as Subsoil. Worn and weather-beaten, this eroded material is a salient part of the environment. 

The majority of subsoil is made up from materials that have undergone the leaching process. This process entails said materials being removed from a solid via percolation. Materials such as clay and sand are most commonly what it comprises of.

What are the properties of subsoil?

  • Less organic matter

Unlike its companion above, subsoil has a significantly lower ratio of organic material. As well as containing less humus, it also contains less plant nutrient content. This goes hand in hand as humus is very nutrient-rich. The smaller amount of humus contained within subsoil is carbon-based and has great longevity.

  • Diverse Colouring

A constant brown colour does feature consistently throughout the varying types. And a combination of brown-yellow or brown-red are the two widespread additional colours. And the colour of is also paramount to indicating the effectiveness of the drainage. The varying moisture levels are revealed easily to the naked eye. The brighter the better! When an increased amount of iron is oxidised it exhibits a more ‘rusty’ colour.

  • Minerals and Materials

For what it lacks in humus, it makes up for in rich minerals. Iron, magnesium and calcium are commonly featured. Roots are therefore rewarded greatly when they venture below the topsoil. And one process that can transfer minerals and materials from the topsoil to the subsoil is Surface runoff. This occurs when a heavy amount of stormy weather/rain hits. When the soil is overly saturated with water, the topsoil can suffer from a shortage of minerals. Because of the increased ratio of clay in the subsoil, a higher volume of water can be held. 

What is it used for?

  • Converting to Topsoil 

Consistent and concerted erosion can niggle away at the topsoil until a small amount if left. If this happens and a solution is needed - subsoil can step up! If a great quantity of organic matter is added, it is plausible. Manure is a popular choice and it must be mixed and combined with the existing matter thoroughly. 

Fertility is also a key aspect of the conversion process. And this can be achieved through liming. Once the conditions are correct for the change, it’s just a matter of waiting. Let the decomposing commence!

  • In Construction

With the advantageous ability that it has to drain water, it is often used in the construction industry. It stores moisture incredibly well as it is particularly dense. After building structures have been completed, topsoil is often added above. This is to encourage growth while giving the area high stability. 

One example of a functional structure created using it is an actual drain! The main purpose being to reduce the likelihood of dampness in buildings. Made from a combination of possible materials including plastic and concrete, they are incredibly effective. But it’s vital not to forget how integral the subsoil underneath is to this system.