CHAPTER - 9 SOIL

1. CHAPTER - 9SOIL

2. 1) Importance of soil :- i) Soil is an important natural resource. ii) Soil helps in the growth of plants by holding the roots and supplying water and nutrients. iii) Soil is essential for agriculture which provides us food, clothing and shelter. iv) Soil is a habitat for several organisms like ants, earth worms, snails, centipeds, millipeds, snakes, rats, beetles etc.

4. Living organisms found in the soil

5. 2) Soil pollution :- Soil pollution is caused by plastics , chemicals, pesticides and other waste products. Soil pollution can be reduced by :- i) Avoiding use of plastics. ii) Treating of wastes and chemicals before releasing into the soil. iii) Reducing use of pesticides. v) Afforestation – planting more trees.

6. 3) Layers of soil :- Activity :- Take a glass tumbler three quarters filled with water. Add a handful of soil in a glass tumbler. Stir it well with a glass rod and leave it undisturbed for some time. We can see different layers of particles of different sizes. The rotting dead plant and animal remains at the top is humus. Below it are layers of clay, sand and gravel. humus water clay sand gravel

7. 4) Soil profile :- A – horizon (Top soil) A vertical section through different layers of soil is called the soil profile. The layers are called horizons. Each layer is different in texture, colour and chemical composition. B – horizon C – horizon Bedrock

8. A – horizon is the uppermost layer of the soil. It is also called top soil. It is dark in colour and rich in humus. It provides nutrients to plants. It is soft, porous and retains more water. B – horizon is the second layer. It has less humus but has more minerals. It is harder and more compact. C – horizon is the third layer. It is made up of small lumps of rocks. The lowermost layer is the bedrock made up of very hard rocks. A – horizon (Top soil) B – horizon C – horizon Bedrock

9. 5) Formation of soil and types of soils :- a) Formation of soil :- Soil is formed formed by the breaking down of rocks into smaller particles by the action of wind, water and climate. This process is called weathering. Soil is a mixture of rock particles and humus.

10. b) Types of soil :- There are three main types of soil. They are sandy soil, clayey soil and loamy soil. i) Sandy soil :- In sandy soil the particles are large in size. They have more space between the particles filled with air. They do not retain water and are light and dry. ii) Clayey soil :- In clayey soil the particles are smaller. They have less space between the particles and has less air. They retain more water and are heavy and wet. iii) Loamy soil :- In loamy soil the particle size is between those of sand and clay. It contains humus and has the right water holding capacity. So it is the best soil for the growth of plants. Sandy soil Loamy soil Clayey soil

11. 6) Properties of water :- ground i) Percolation rate of water :-(How fast water passes through the soil) Water percolates faster through sandy soil and slower through clayey soil. Activity :- Take a PVC pipe about 20 cm long and 5 cm diameter. Place it about 2 cm in the ground. Pour 200 ml water slowly into it and note the time taken for the water to percolate. The rate of percolation of water can be calculated by using the formula Amount of water (mL) Rate of percolation = Percolation time (min) ground

12. water drops ii) Moisture in the soil :- soil Soil contains moisture. The amount of moisture is different in different types of soils. Clayey soil contains most moisture And sandy soil contains least moisture. Activity :- Take some soil in a boiling tube and fix it to a stand. Heat the soil with a burner. Drops of water are formed in the boiling tube. The water from the soil evaporates and condenses in the inner walls of the boiling tube. This shows that soil contains moisture.

13. dropper iii) Absorption of water by the soil :- soil filter paper . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . funnel Soil absorbs water. Clayey soil absorbs most water and sandy soil absorbs least water. Activity :- Take a funnel. Fold a filter paper and keep it in the funnel. Weigh 50g dry soil and pour it in the funnel. Measure a certain amount of water in a measuring cylinder. Pour it drop by drop all over the soil till it starts dripping. Subtract the amount of water left in the measuring cylinder from the . . . . . . . . . . original amount. This is the amount of water . . . . . . . . . . absorbed by the soil. Calculate the percentage of water absorbed by the soil. Weight of soil = 50 g Initial volume of water = U mL Final volume of water = V mL Volume of water absorbed by the soil = (U – V) mL (U – V) Percentage of water absorbed = X 100 50 beaker

14. 7) Soil and crops :- Wheat Paddy Cotton Peas Different types of crops are grown in different types of soils. Clayey and loamy soils are suitable for growing wheat and pulses. Clayey soil containing organic matter is suitable for growing paddy. Sandy and loamy soils are suitable for growing cotton.