Soil Formation and Composition (PDF)

Soil forms the topmostayer ofthe Earth's surface which contains water, minerals and gas. and provides the basis of life. Soil forms from rocks. Large rocks break down into smaller pieces by the action of the heat, wind and water. These small pieces collide against the ground and each other, and get...

Soil forms the topmostayer ofthe Earth's surface which contains water, minerals and gas. and provides the basis of life. Soil forms from rocks. Large rocks break down into smaller pieces by the action of the heat, wind and water. These small pieces collide against the ground and each other, and get converted intofine particles. These fine particles mix with humus, remains of dead plants and animals, to form soil. This process of formation of soil is called weathering. Soil supports life 53  Well. What makes soil such an important natural resource? support. there are nmany factors. It provides the plants physicalsupplies roots. Soil as plants are anchored in the soil by theircssential for their water and nutrientsto plants, which are on Earth. They growth. IPlants are the primary producers Soil is home to provide food for aninmals and human beings. shelter in soil. many animals. These animals find food and Activity air. PLAN: To observe that soil contains SUPPLIES: Soil sample, aflower pot, water pot. Pour water into the soil. WORK IT oUT: Put thesoil in the flower soil contains air. The OuTCOME: Bubbles Would appear. It means soil particles. The in the bubbles appear due to the air spacesearlier filled with air. water fills up the spaces which were Types of soil due to various The types of soilvary from place to place the local soil-forming conditions such as climate, rock type and soil is processes. Depending on their external appearance,and clay. categorised intothree types, namely. gravel, sand Gravel cannot Gravel is composed of tiny stones that are hard and water hold water. The gaps berween the stones in gravel allow to pass easily. Sand Sand is a loose mass of mineral materials in the form of fine granules. Water can easily pass through this kind of soil. Clay The particles of clay are so small that they can be easily carried by water or the wind through long distances. When mixed with water, clay becomes very heavy and sticky. \Waer cannot pass through this type of soil casily, Compo[ition of soil Soil is composed of gravel, sand, clay, humus, air, water, minerals and microorganisms. Soil containing sand, clay and humus is called loam. This kind of soil is very good for growing plants.  Soil profile Soil profiles tell us atbout the layers of the soil. Topsoil The top layer of soil is called the topsoil. It Contains more humus than any other lzyer. Topsoil Humus provides nutrients to the soil. These nutrients are nccded by plants to grow. Topsoil also holds most of the roots of plants. Subsoil The layer beneath the topsoil is called the Subsoil subsoil. Itis harder and more ompact thanrich the topsoil. It does not have much humus. It is in soluble mincrals. Bedrock consists of The lowest layer of soil is bedrock. It Rainwater small pieces of rocks. It is non-porous. Bedrock gathers over it to form the water table. Soil erosion Loose and uncovered topsoil is carried away by strong wind erosion. and water. This removal of the topsoi is called soil Cutting down of trees and overgrazing are its main causes. Soilerosion leaves infertile subsoil that is not fit for growing and cultivating plants and crops. Soil conservation Soil is important for the growth of plants. It provides all by air theessential nutrients that a plant needs to prepare food. Therefore, soil erosion should be prevented. The method of protecting the soil from erosion is known as soil conservation. Soil can be conserved by: Planting more number of trees in forest areas to replace the ones that are cut down. Growing different types of crops ona farnmland to recover water itsfertility. This method is also known as crop rotation. Building of dams across rivers to prevent floods. 55