What is soil?
Photograph of three tall glass tubes filled with soil and water to show the seperation point between settled soils and water. Left to right: sand, silt, and clay.Soil, is made from rocks that break apart or wear away over many years. This is referred to as weathering. It may take 100 to 1,000 years for 1 cm of soil to form through weathering. Soil also contains air, water, and humus, the decayed remains of dead animals and plants. Soil can actually be separated into 5 main parts. They are: • Humus: A dark, moist soil composed of bits of dead, rotting insects, animals, leaves, roots, sticks, and food. Humus adds nutrients to the soil which plants need to grow and live. • Clay: A soil that holds water. When wet, clay feels slippery and slimy. It is made of particles that are smaller than 0.004 millimeters. • Silt: Soil that looks like fine grains or tiny pieces of rock. Particles classified as silt measure from 0.004 millimeters to 0.006 millimeters. • Sand: Soil that is coarse and drain
Soil is one of the three major natural resources, alongside air and water. It is one of the marvellous products of nature and without which there would be no life. Soil is made up of three main components – minerals that come from rocks below or nearby, organic matter which is the remains of plants and animals that use the soil, and the living organisms that reside in the soil. The proportion of each of these is important in determining the type of soil that is present. But other factors such as climate, vegetation, time, the surrounding terrain, and even human activities (eg. farming, grazing, gardening etc.), are also important in influencing how soil is formed and the types of soil that occur in a particular landscape. Soil can form from the rocks below, or from rocks a very long distance away – perhaps being carried by wind or water. The glaciers of the last ice age acted as giant bulldozers pushing truly huge amounts of soil along as they grew and dropping the soil as they melted.
Soil scientists define soil in various ways, but all definitions illustrate the fact that soil is not as simple as many assume. Soil is the uppermost layer of material covering most of the earth’s land surface and consists of mineral particles, organic matter, microorganisms, water and air. The possible types and proportions of these components are innumerable and why so many different types of soil exist. Soil scientists divide soil into layers they call horizons. The A horizon is the uppermost several inches and consists mostly of what we know as topsoil. It is often darkly colored and rich in organic matter, and it usually provides a favorable environment for plant growth. The next two layers, the B and C horizons, are lighter in color, lower in organic matter and relatively infertile. We call the B and C horizons the subsoil. Plant roots generally extend through the A horizon and well into the B horizon. However, the C horizon, which may be well below the surface, is comparatively
