NCERT 8th Class (CBSE) Science: Crop Production

Question: What are weeds? How can we control them?

Answer: Any unwanted plant which grows along with crops is called weed. Removal of weeds is called weeding. Weeding is usually done manually or by using a trowel. Weeds are also removed during ploughing. Weedicides are the chemicals which destroy weeds. Weedicides are sprayed before flowering and seeding in weeds.

Question: Explain the structure of a plough.

Answer: A plough is composed of ploughshare and ploughshaft. The ploughshare is triangular in shape and is made of iron. The ploughshaft is made of wood and is very long. It is harnessed to a pair of bullocks or other cattle with the help of a beam.

Question: Explain the structure of traditional seed drill.

Answer: The traditional seed drill is composed of a funnel with a long and pointed neck. It is attached to the ploughshaft. Seeds are kept in the funnel and they drop slowly through the neck, while the field is being tilled. The pointed neck of the seed drill pierces the soil and seed goes deep into the soil.

Question: What is the significance of ploughing?

Answer: Significance of Ploughing:

1. This allows the roots to penetrate deep into the soil.
2. Loose soil allows the root tips to breathe easily when they go deep into the soil.
3. It allows proper mixing of nutrients from humus into the soil.
4. Loosening of soil brings nutrients and minerals to the top and thus plants are able to utilize these minerals.

Question: Write a brief note on fertilizers.

Answer: Fertilizers are human made chemical substances that contain one or more nutrients essential for plant growth. They are made in factories. The most widely used fertilizer are NPK fertilizers that are rich in nitogen (N), phosphorous (P) and potassium (K) salts. They are easy to store and handle. Since they are soluble in water, they are directly absorbed by plants and greatly increase crop yields. Some other examples of fertilizers are urea, ammonium sulphate, super phosphate, potash etc.. However, if overused, fertilizers harm the soil by making it porous. Excess fertilizers get washed into water bodies and harm aquatic animals.