CLASS VIII | SCIENCE | CHAPTER 1
Notes prepared by Subhankar Karmakar
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Lecture 3:
ADDING MANURE AND FERTILISERS
1. NEED OF MANURE & FERTILISERS
Repeated growing of crops in the same field removes a lot of precious mineral elements, organic matter and other materials from the soil. The deficiency of plant nutrients and organic matter in the soil is made up by adding manures and fertilisers to the soil.
2. MANURES:
Manure is a natural fertiliser. A manure is a natural substance obtained by the decomposition of animal wastes like cow-dung, human wastes and plant residues, which supplies essential elements and humus to the soil and makes it more fertile.
3. PREPARATION OF MANURES:
Manures are prepared from animal wastes, human wastes and plant residues by the action of micro- organisms. In order to prepare manure, farmer dump animal wastes and plant wastes in pits at open places and allow it to decompose slowly. The decomposition is carried out by some micro-organisms. The decomposed animal and plant matter is used as organic manure.
4. FUNCTION OF MANURES:
Manures provide a lot of organic matter like humus to the soil. A manure improves the soil texture for better retention of water and aeration.
5. CHEMICAL FERTILISERS:
A chemical fertiliser is a salt or an organic compound containing the necessary plant nutrients like nitrogen, phosphorus or potassium, to make the soil more fertile. A chemical fertiliser is rich in a particular plant nutrients such as nitrogen, phosphorus or potassium (NPK). Some examples of chemical fertilisers are Urea, Ammonium sulphate, Superphosphate, Potash and NPK.
6. DIFFERENCES BETWEEN MANURES AND FERTILISERS:
1. A manure is a natural substance obtained by the decomposition of animal wastes like cow dung, human waste and plant residue.
But a fertilizer is a salt or an organic compound.
2. Manure is not very rich in essential plant nutrients like nitrogen, phosphorus and potassium where as fertilizers are very rich in plant nutrients like nitrogen, phosphorus and potassium.
3. A manure provides a lot of organic matter like humus to the soil but a fertilizer does not provide any humus to the soil.
4. A manure is absorbed slowly by the plants because it is not much soluble in water but being soluble in water if fertilizer is readily absorbed by the plants.
5. Menure can be prepared in the field but fertilizers are prepared in factories.
7. ADVANTAGES OF MANURE:
Organic manure is considered better than Fertilisers because of the following reasons:
1. Manure enhances the water holding capacity of the soil.
2. Manure makes the soil porous due to which the exchange of gases becomes easy.
3. Manure increases the number of useful microbes in the soil.
4. Manure improves the texture of the soil.
8. LEGUMINOUS CROPS:
The pulses, peas, beans, groundnut, gram and clover are called leguminous crops. Leguminous crops have the ability to fix atmospheric nitrogen to form nitrogen compounds. The planting of leguminous crops in a field has the same effect as adding nitrogenous fertiliser in the field.
9. CROP ROTATION:
The practice in which different types of crops like leguminous crops and non-leguminous crops are grown in the same field or soil is called crop rotation. In crop rotation, cereal crops like Wheat, Maize, Paddy and Millet are grown alternately with leguminous crops pulses, peas, beans, groundnut and clover etc. in the same field.
10. ADVANTAGES OF CROP ROTATION:
Rotation of crops has the following advantages:
1. Rotation of crops improves the fertility of the soil and hence increases the production.
2. Rotation of crops saves a lot of nitrogenous fertiliser.
QUESTIONS BANK:
21. Why does soil needs manuring?
22. What are manures? Why it is needed?
23. What are the advantages of manures?
24. What are chemical fertilisers? Give examples.
25. Differentiate between manures and fertilisers.
26. What are leguminous plants? What they are being planted in the field?
27. What are crop rotation? What are their advantages?
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