question_answer 73)

  Figure shows the two crop fields [Plots A and by have been treated by manures and chemical fertilizers respectively, keeping other environmental. factors same. Observe the graph and answer the following questions. (i) Why does plot B show sudden increase and then gradual decrease in yield? (ii) Why is the highest peak in plot A graph slightly delayed ? (iii) What is the reason for the different pattern of the two graphs?

Answer:

  (i) Plot B refers to chemical fertilisers which give short-term benefits because they are nutrient specific. The continuous use of fertilisers in an area destroy soil fertility so there is gradual decrease in yield after sometime. (ii) Manures help in enriching soil with nutrients and organic matter and increase the soil fertility. They also improve the soil structure. The plot A demonstrates the trend that the addition of manures into the soil have long term benefits in terms of high yield. (iii) Manures are natural ways of enriching the soil whereas fertilisers are commercially produced plant nutrients. They do not have organic matter like in manure to replenish the soil with useful microbes. Therefore, in plot A manures give high yield while plot B gives high yield for a short time and then it decreases.