Observe the graph and answer the
following questions
(a) Why does plot B show sudden increase
and then gradual decrease in yield?
(b) Why is the highest peak in
plot A graph slightly delayed?
(c) What is the reason for the
different pattern of the two graphs?
Answer:
(a) The process of preparation
of compost by using earth worms, which hasten the process of decomposition of
plant and animal refuse is called vermi-compost. (1)
(b)
(a) Sunhemp (b) Dhaincha 
(c)
Storage structures for grains should be air-tight, easy to clean, moisture
proof and rodent proof. (1)
(d)
Rhizobium and Nitrosomonas
(e)
Leguminous crop. (1)
Or
(a)
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
inthe graph may be due to continuous use and highquantity of chemicals which
kills microbes usefulfor replenishing the organic matter in the soil. This decreases
the soil fertility. 
(b)
Manures supply small quantities of nutrients to the soil slowly as it contains
large amounts of organic matter.
It
enriches soil with nutrients; there by increasing soil fertility continuously.
(c)
The differences in the two graphs indicate that use of manure is beneficial for
long duration incropping as the yield tends to remain high when the quantity of
manure increases.
In case of plot B the chemical fertilizers
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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