Question

The following figure shows the two crop fields (Plots A and B) have been treated by manures and chemical fertilisers respectively, keeping other environmental factors the same. Observe the graph and answer the following questions.

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

Answer 1

With addition of chemical fertilizers there is sudden increase in yield due to release of nutrients N, P, K etc. in high quantity which are absorbed by the roots quickly. The gradual decline in the graph may be due to continuous use and high quantity of chemicals which kill microbes useful for replenishing the organic matter in the soil. This decreases the soil fertility.