Question

Figure15.1 shows the two crop fields [Plots A and B] have been treated by manures and chemical fertilizers respectively, keeping other environmental factors the same. Observe the graph and answer the following questions.

(i) Why does plot B show a sudden increase and then a gradual decrease in yield?

(ii) Why is the highest peak in plot A graph slightly delayed?

(ii) What is the reason for the different patterns of the two graphs?

Answer 1

(i) In plot B, chemical fertilisers were added. With the addition of chemical fertilisers, the yield of the crop increased initially, but with the continued use of chemical fertilisers, the crop yield decreased significantly. This happened because chemical fertilisers are nutrient specific and give only short-term benefits. Their prolonged use destroys soil fertility and cause a gradual decline in crop production.

(ii) In plot A manures were used to improve the soil fertility. Manures are a rich source of organic matter and release nutrients slowly in comparison to fertilities. Therefore the highest peak in the plot of the graph is slightly delayed. Manures enrich the soil with nutrients and organic matter, which further increases soil fertility. Manure also improve the soil structure. The addition of manure into the soil have long term benefits and improve soil fertility which considerably increased crop yield.

(iii) Manures are natural ways of enriching the soil with organic nutrients, whereas chemical fertilisers are chemicals that enrich the soil with a particular element. Fertilisers have an adverse effect on soil fertility as their prolonged use can kill the useful microorganisms present in the soil and ultimately make the soil unfit for sustaining plant life and their prolonged effects include reduction in crop productivity.
Manures, on the other hand, improves soil fertility by adding organic nutrients to the soil and their prolonged use will cause crop production to increase.