Answer:
(i)
With the addition of chemical fertilisers 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.
(ii) Manures supply small quantities of nutrients to the soil slowly as
it contains large amounts of organic matter.
It enriches soil with nutrients; thereby increasing soil
fertility continuously.
(iii) The differences 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 fertilisers 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. (2)
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