Soil
Soil is a thin layer of material on the Earths surface . Plant have their roots in the soil and cannot grow without it. People and animals use plants as a food source so soil is a very important natural resource.
Soil Formation
Soil formation is influenced by a number of different factors.
Climate - The rate at which parent rock is broken down to form mineral matter by weathering depends on the amount of rainfall and the temperature. Too much rainfall can lead to leaching. Freeze-thaw action occurs in areas with cold climates and chemical weathering helps to break down the parent rock in areas with hot climates.
Parent Material - Parent Material refers to the type of rock that is broken down by weathering to form soil. The minerals from the broken down rock provide nutrients for the soil. Soils that form on limestone are fertile.
Living Organisms - Living micro-organisms in the soil such as bacteria and fungi break down plant litter in the O horizon. This creates humus and makes the soil more fertile.
Landscape/Relief - Soils in upland areas are generally thin because of mass movement. They are also poorly drained because of heavy rainfall in upland areas. Soils in lowland areas are deeper well drained and generally more fertile. They are rich in humus because there is more plant litter and living organisms.
Time - It can take up to four hundred years for one centimetre of soil to form because the process is slow. As soil is a non renewable resource we must make sure that we do not over exploit it.
Vegetation - vegetation in the area creates litter, which breaks down into humus. Humus makes soil fertile. Areas with deciduous trees have more plant litter than areas with coniferous trees. That means that areas with decidous trees have more fertile soils.
Soil Composition
Soil is made up of five main ingredients.
Mineral Matter - Mineral mater is the main ingredient in soil. it is made up of rock particles that have been washed and eroded. It includes stones, sand, silt and clay. it provides the minerals that help plants to grow.
Air - Air fills the space between the particles of rock in the soil. Air contains oxygen and nitrogen. Plants need oxygen and nitrogen to grow. Living organisms need them to survive in the soil.
Water - Water helps to bind the soil together. Minerals dissolved in water are absorbed through the roots of plants and help them grow.
Humus - Humus is a dark jelly like substance that forms when plants and animals decay and rot. Humus binds the soil together and provides nutrients that makes the soil fertile.
Living Organisms - Soil is home to many types of living things such as earthworms and various bacteria, fungi, insects and burrowing animals. These living organisms break down plant and animal remains to form humus. They also mix up the soil yo make it easier for water to pass through.
Soil Profiles
O Horizon
This layer contains organic matter. Leaves and rotting vegetation are called plant litter and this provides the humus for the soil.
A Horizon
This is the upper layer of the soil and is called the topsoil. This is where most of the organisms in the soil live. It is usually darker than the other layers because it has the highest humus content. It is the most fertile part of the soil.
B Horizon
This layer is called the subsoil. It is lighter in colour than the A Horizon because there is Less humus here. This layer has more stones because it is located closer to the bedrock and because it is protected from weathering by the A horizon.
C Horizon
This is the bedrock or the parent material. The lower layer consists of solid rock but the upper section may be broken down into rock particles. In some instances the parent material can actually be a different rock deposited on top of the bedrock by glacial deposition.
Leaching
When rain falls, water passes through the soil, washing minerals, humus and nutrients from the A horizon down into the B horizon. This process is called leaching. Most plant roots are located in the A horizon and leaching can sometimes interfere with their growth if nutrients are washed beyond their reach. Sometimes in extremely wet conditions minerals build up at the bottom of the A horizon. They can become cemented together to create hardpan. this is an impermeable layer that water is unable to flow through and so the soil above the hardpan becomes waterlogged.
Types of Soil in Ireland
Brown Earth Soils
Brown Earth Soils are the most common soil types in Ireland. They are mostly found in lowland areas in the Irish midlands. Brown Earth soils developed on the boulder clay that was deposited at the end of the last Ice Age. They contain fairly even amounts of sand silt and clay and have a loam texture.
Deciduous forests developed on this soil and the plant litter from the leaves that fell from the trees every year provided material for the formation of humus. This is why brown Earth soils have a dark colour. Very little leaching occurs in these areas so the soil remains fertile.
over time the forests were cleared for agricultural land. The land is now used for intensive arable and pastoral farming. Farmers add nutrients to the soil in the form of manure and fertilisers because the level of plant litter is no longer as high as it was when theses soils were formed.
Podzol Soils
Podzol soils are found on the floors of coniferous forests in cold and wet areas. Coniferous forests floors have little plant litter, and therefore small amounts of humus. The cold and damp conditions means that there is also little earthworm activity.
Heavy rainfall causes a lot of leaching, and nutrients are washed through the A horizon often creating hardpan. This gives the A horizon a grey colour.
Podzols are quite infertile and acidic. They tend to be heavy soils and their texture has more clay particles than sand and silt. They are found in poorly drained upland areas of Galway and Cork.
Gley Soils
gley soils are grey in colour. They develop where the bedrock or the clay above it is impermeable. They are sticky and waterlogged. This makes it difficult to grow crops on the land and so it is used for only pastoral farming.
Peaty Soils
peaty Soils are dark in colour. They develop in cold upland areas with high rainfall and lowland areas with poor drainage. These soils are waterlogged and full of organic matter that has not broken down. They are a valuable source of fuel and are found in blanket and raised bogs.