Class 7 Notes on Soil
Notes on Soil Class VII
What is the soil composed of?
The soil is made up of two main components:
• Tiny bits of mineral particles, which come from larger rocks. These minerals include salts of iron, calcium, potassium, magnesium and phosphorus, etc. Many of these minerals are needed by plants for their growth.
• Another component is humus, which is dark brown in colour and consists of decaying remains of plants and animals. A variety of dead and decaying organisms contribute to the formation of humus. A lot of humus is formed by decaying leaves of plants. Small plants, such as mosses, lichens and ferns, grow on small pieces of rocks. When they die, they mix with the soil and form humus. Soil also contains water, air and living organisms. Hummus makes the soil fertile by providing organic nutrients. It also provides food to earthworms and other animals living in the
soil. Besides earthworms, other organisms living in the soil include millipedes, centipedes, ants, fungi and bacteria.
Earthworms are also called as ‘farmer’s friend’. They improve the texture of soil By burrowing into the soil, they make it lose, thus allowing air to enter into it and water to drain from it. They also form channels in the soil for roots to spread through.Scientists have estimated that every Gram of soil contains about a billion (100 crores) bacteria.
Do you know?
Bacteria and fungi in the soil feed on dead remains of plants and animals and help to form humus. Some bacteria convert nitrogen of the air into nitrogen compounds, which can be used by plants, This is known as the fixing of
nitrogen. Some organisms such as millipedes and centipedes, living in the soil, are harmful as they destroy roots of plants.