Figure 15.1 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.
(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?

Dear Student,

i) The plot B show a sudden increase after the addition of fertilizer which suggests that the crop plants utilize the nutrients present in the chemical fertilizers such as nitrogen, potassium, etc. The further gradual decrease in yield showed that the chemical fertilizers are lethal to useful microbes present in the soil which result in the decreased soil fertility.

ii) The plot A represent the crops treated with manure. Manure is a natural fertilizer. A slight delay in the highest peak in plot A graph shows that the natural fertilizer, manure, supply nutrients to the soil at a slow rate. This helps in increasing the fertility, organic content and useful microbial growth. 

iii) The different pattern of the two graphs indicates that the type of fertilizer (chemical or natural) used directly affects the quality and quantity of the crops and their yield. When natural fertlizer is used, it provides more benefits for longer duration whereas the use of chemical fertilizers provides benefit only for short duration and damages the crop as well as the quality of the soil.


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