Most of the dry land on the earth is covered with soil.
Soil is made when rocks break and crumble.
Plants grow in soil.
Soil is the home for millions of animals.
Soil erosion is the wearing away of soil by wind and water.
What is soil?
Rocks are broken by earthquakes and volcanoes. Rain, frost, sun, wind, water and ice all help to break up the rocks. It takes thousands and thousands of years for the rocks to turn into soil. This is called weathering.
When plants die they rot in the soil. Rotting plants change into humus. Humus and plants hold the soil together. Humus makes the soil healthy for new plants. The healthier the soil, the healthier will be the plants that grow in it.
Ploughing prepares the soil for plants.
The soil is the home for millions of animals. These animals make burrows and tunnels under the ground. Burrowing and crawling through the soil, the animals turn it over and mix it up. Air for the animals to breathe gets into the soil. The roots of plants need the air too. Rainwater runs into the soil and waters the plants.
Before a farmer plants crops, the soil is ploughed. Ploughing beaks up the soil and makes spaces for air and water which the plants will need as they grow.
Types of Soil
Soil is made up of finely ground rock particles. There are three main types: clay, silt, and sand. Each kind can be identified by the size of its particles, by its texture and by tests that show:
(a) how long particles stay suspended in water
(b) the ribbon test, which tests whether or not the soil stays in a ball when moist and squeezed tight.
Most soils are a combination of the three types of particles.
Clay
Because clay particles bond together tightly, it is good for making pottery. Getty Images
Clay particles are the smallest and lightest. When suspended in water, clay particles are generally the last to settle on the bottom. The texture is sticky when moist, but hardens and cracks when dry.
There is not much space between the clay particles, so it is difficult for plants to grow and survive because it is hard for the roots to penetrate the clay, and for air to circulate through it.
Moist clay can be pressed into a ball, and because the particles bond tightly, it is good for making pottery.
Silt
Silt particles are medium-sized. The texture is smooth and slippery. When suspended in water, silt particles will settle after sand, but before clay. When moist, silt cannot be pressed together to form a ball. Silt particles do not hold together as strongly as clay and are more easily eroded (washed or blown away) by water and wind than clay. Silty soils hold water and nutrients well and are good for growing plants.
Sandy soils are not good for growing plants and are easily affected by erosion. Getty Images
Sand
Sand particles are the largest of all soil particles, and the texture is gritty. There are larger spaces between the particles. When suspended in water, sand generally falls to the bottom first. When moist, the sandy soil will not form a ball when squeezed and falls apart. The soil does not hold much water.
Loam is a combination of soils
Loam is a combination of soil types so the particle size varies and the texture is neither gritty nor smooth. When loam is suspended in water, the different soil particles settle in fairly equal layers. Loam is excellent for growing plants because the sand helps lighten the soil, the clay helps bind the particles together and holds water, and the silt helps hold nutrients needed by plants and animals.