NCERT Class-9 Science Solutions: Chapter 15-Improvement in Food Resources Part 9 (For CBSE, ICSE, IAS, NET, NRA 2022)

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Question 46:

What would happen if poultry birds are larger in size and have no summer adaptation capacity? In order to get small sized poultry birds, having summer adaptability, what method will be employed?


Maintenance of temperature is needed for better egg production by poultry birds. Therefore, larger size (increase in surface area of body) and no adaptability of summer may cause decline in egg production. To obtain the smaller size and higher summer adaptability, cross breeding of poultry birds are done. Small size is also needed for better housing and low feed.

Question 47:

Suggest some preventive measures for the diseases of poultry birds.


Some preventive measures of poultry bird diseases are

  1. Cleaning of poultry farms
  2. Proper sanitation of poultry farms
  3. Spraying of disinfectants at regular intervals
  4. Appropriate vaccination of birds.

Question 48:

Figure shows the two crop fields [Plots A and B] have been treated by manures and chemical fertilizers respectively, keeping other environmental factors same. Observe the graph and answer the following questions.

  1. Why does plot B show sudden increase and then gradual decrease in yield?
  2. Why is the highest peak in plot A graph slightly delayed?
  3. What is the reason for the different pattern of the two graphs?
Image Quantity of Amendment


  1. With addition of chemical fertilizer there is sudden increase in yield due to release of nutrients N, P, K etc. in high quantity. The gradual decline in the graph may be due to continuous use and high quantity of chemicals which kills microbes useful for replenishing the organic matter in the soil. This decreases the soil fertility.
  2. Manures supply small quantities of nutrients to the soil slowly as it contains large amounts of organic matter [Hint: importance of organic matter can be included] . It enriches soil with nutrients thereby increasing soil fertility continuously.
  3. The difference in the two graphs indicate that use of manure is beneficial for long duration in cropping as the yield tends to remain high when the quantity of manure increases.

In case of Plot B the chemical fertilizers may cause various problems when used continuously for long time. Loss of microbial activity reduces decomposition of organic matter and as a result soil fertility is lost that affects the yield.

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