NCERT 8th Class (CBSE) Science: Crop Production

Question: What are the advantages of ploughing the soil before sowing seeds?

Answer: The process of loosening and turning the soil is called tilling or ploughing. This has the following advantages:

1. Loose soil has a lot of air trapped in it, which is used by the roots to breathe easily.
2. Loose soil allows the roots to penetrate deeper, thus securing the plant more firmly.
3. Loose soil helps the growth of earthworms and microbes in the soil. They provide nutrients to the soil and aid in further loosening of the soil.
4. Turning and loosening of soil brings nutrient-rich soil to the top. Plants can then absorb these nutrients more efficiently.
5. Loose soil mixes more uniformly with fertilizers.

Question: What precautions must be kept in mind while sowing seeds in a field?

Answer: While sowing, the following points need to be kept in mind:

1. Seeds should be of good quality, healthy and free from diseases.
2. They must be planted at the proper depth in the soil. If planted deep in the soil, they cannot respire, and their shoots may not be able to push through the soil. If planted on the surface, they will be eaten by the birds.
3. Seeds require water for germination. The soil should, therefore, have water in it. However, if there is too much water, seeds will not germinate properly.
4. Seeds should be sown at proper distances. If they are too close they will not get enough water, sunlight and nutrients. If they are too far apart, there is wastage of field space.

Question: Discuss two natural methods of manuring.

Answer: Two natural methods of manuring are:

1. Manures: Manures are organic substances obtained from dead plants and animal wastes. Green manure is made from crops grown specially to be ploughed into the soil while still green, i.e. legumes, rye grass, fenugreek, etc., to improve the fertility of the soil.
2. Animal manure consists of animal wastes. Compost is a manure obtained by the decomposition of dead plants and animal waste. Compost is made by burying all available organic materials in a pit with alternating layers of soil, and leaving it to rot. Bacteria and fungi in the layers of soil speed up the decomposition. Compost is rich in organic nutrients but not in some important nutrients like nitrogen, phosphorus and potassium.

Question: Draw a labelled diagram to illustrate the nitrogen cycle.

Answer: