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class 8 cbsc science chapter one pdf solutions below

ch 1 crop production and manegment

CROP PRODUCTION
1. What are Weeds?
Ans-- Weeds are unwanted plants that grow along with the crops.

2. Why should grains be dried before the storage?
Ans--This prevents the grains from getting spoilt by microbes.

3. What is hybridization?
Ans-- This is a technique used for developing new varieties of crops by cross breeding two different varieties.

4. List the steps involve in nitrogen cycle.
Ans-- Nitrogen fixation, nitrogen assimilation, ammonification, nitrification, denitrification.

5. What enables leguminous plants to fix nitrogen?
Ans-- The root nodules of leguminous plants contain nitrogen fixing bacteria, called rhizobium. These bacteria can fix atmospheric nitrogen into nitrates.

6. What is animal husbandry?
Ans--The breeding, feeding and caring of domestic animals for food and other purposes is called animal husbandry.
D
. 1. Distinguish between kharif crops & rabi crops, giving two examples each.
Ans-- Kharif crops
(i) These crops are sown at the beginning of south-west monsoon.
(ii) They are grown during June to October. Examples: Paddy, maize, millet, etc.
Rabi crops
(i) These crops are sown at the beginning of the winter season.
(ii) They are grown during November to April. Examples: Wheat, pea, gram,
sugarcane, etc.

2. List the steps involve in crop production, in sequential order.
Ans--The steps involved in crop production are:
(i) Preparation of soil (ii) Seed selection and sowing (iii) Manuring (iv) Irrigation (v) Weeding (vi) Protection from pests and diseases (vii) Harvesting, threshing and winnowing (viii) Storage

3. Why do farmers normally use manures & fertilizers in their fields?
Ans--Manures are natural organic substances rich in humus. Fertilizers are rich in inorganic nutrients. Plants require both these types of nutrients. So farmers normally use a mixture of manures and fertilizers.

4. What is water logging? How does it harm the crops? How can it be prevented?
Ans--The problem created in the field by excessive supply of water is called waterlogging of the field. It harms the crops by replacing air in the soil with water, which reduces the supply of air to the roots of plants. This stops the growth of the plants. It also increases the amount of salt in the soil which is harmful for the crops. To prevent waterlogging, it is necessary to have adequate drainage in irrigated fields.

5. Discuss two methods of weeding in which poisonous chemicals are not used.
Ans--The followings are the two methods of weeding in which poisonous chemicals are not used:
(i) By pulling the weeds out by hand or
(ii) By using a trowel or a harrow to uproot weeds from a field.

7. Differentiate between nitrification & denitrification.
Ans-Nitrification (i) The process of conversion of ammonia into nitrates is called nitrification. (ii) This process requires oxygen. (iii) Nitrification is done by nitrifying bacteria. (iv) Here the product nitrates are absorbed by plants. Denitrification (i) The process of conversion of nitrates to free nitrogen gas is called nitrification. (ii) This process does not require oxygen. (iii) Denitrification is done by denitrifying bacteria. (iv) Here the product mixes in air

E

. 1.What are the advantages of ploughing the soil before sowing seeds?
Ans--The advantages of ploughing the soil before sowing seeds are: (i) Loose soil has a lot of air trapped in it, which is used by the roots to breathe easily. (ii) Loose soil allows the roots to penetrate deeper, thus securing the plant more firmly. (iii) 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. (iv) Turning and loosening of soil brings nutrient-rich soil to the top. Plants can then absorb these nutrients more efficiently. (v) Loose soil mixes more uniformly with
fertilizers

Answers

Answered by nishanikumari23

Explanation:

Ans-Nitrification (i) The process of conversion of ammonia into nitrates is called nitrification. (ii) This process requires oxygen. (iii) Nitrification is done by nitrifying bacteria. (iv) Here the product nitrates are absorbed by plants. Denitrification (i) The process of conversion of nitrates to free nitrogen gas is called nitrification. (ii) This process does not require oxygen. (iii) Denitrification is done by denitrifying bacteria. (iv) Here the product mixes in air E. 1.What are the advantages of ploughing the soil before sowing seeds?Ans--The advantages of ploughing the soil before sowing seeds are: (i) Loose soil has a lot of air trapped in it, which is used by the roots to breathe easily. (ii) Loose soil allows the roots to penetrate deeper, thus securing the plant more firmly. (iii) 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. (iv) Turning and loosening of soil brings nutrient-rich soil to the top. Plants can then absorb these nutrients more efficiently. (v) Loose soil mixes more uniformly with

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