St Mary's Learning Support Department: Soils

"The soil is not a mass of dead debris, merely resulting from the physical and chemical weathering of rocks; it is a ....system which has resulted from the decomposition of plant and animal remains. It is teeming with life"

Selman Waksman

Soil, like air and water, is one of the world's most important natural resources. Because it lies beneath our feet and is often hidden by buildings and roads we may not often think about how much it affects our lives and how much we depend on it.

Most of our food depends on soil - it is where we find the plants and many of the animals which make up our food, and it is home for billions of organisms. Soil also gives support for many of our buildings and structures.

Soils form very slowly, maybe as little as 1 cm of thickness in 500 years, so we can't just replace them in our own lifetime. Many of our soils are becoming damaged and are at risk.

It is important that we understand our soil and make sure it is there for future generations.
Soil is composed of a number of things. There are mineral particles from rocks that have been denuded by weathering over the years. There is also dead plant material. This is broken down into something called humus which we also find in soil. Micro-organisms break down the dead plant material or litter into humus. Humus holds soil particles together. There is also air in soil to allow the micro-organisms to breathe. Water is also present in soil. The mineral particles in soil are absorbed by water which in turn is absorbed by plants through their roots.

Brown soils are very fertile. Ireland is lucky to have a wide area of brown soils.

Soils form an almost complete skin over the earth, broken only by oceans and other water bodies and by mountains that have yet to develop a soil cover. When you walk through your garden or through fields and woods there is always this amazing carpet, called soil, beneath your feet. But how do soils form?

Firstly, the climate provides agents of weathering like frost, heat and temperature changes that break up rocks over time into mineral particles. Secondly, vegetation which dies is turned into humus by micro-organisms. Thirdly, people can have a major effect on soils. If we over cultivate soils they can loose all their water and minerals. This is what happens when desertification occurs. But people can help soil by allowing it to rest from crop growing or by replenishing it with fertilisers.

There are many different types of soil. some are very fertile and very good for growing crops. Other are not. Brown soils are the best. The other main soils in Ireland are Podzols, Gley and Peaty soils.

While Brown soils are fertile because of the humus in them created by falling leaves, Podzols are different. They are not as fertile. They have less humus because they are in areas of coniferous trees where not as many leaves fall to create humus. Gley soils are in areas where drainage is poor and much of the nutrients or humus in the soil has been washed down to the bottom of the soil profile through a process called leaching.

Podzols are grey and not very fertile.

Peaty soils are found in bogs. They were made from decomposed plant remains over thousands of years. These soils are often dug out of the Earth as turf and are used as fuel such as peat briquettes or as garden compost.