Class 8 science chapter 1 extra questions part 3

Q. 1. Give the role of manure and fertiliser in the soil.
Answer: Manures are substances added to the soil to add organic matter such as 
carbon. Hence, manure enhances soil fertility which is dependent on the interaction of 
various organisms and reactions. Fertilizers are chemical compounds. It provides 
specific nutrient such as nitrogen (N), phosphorus (P) and potassium (K) to the soil. 
Fertilizers increase crop production but it harmful for the soil and environment if it is 
used continuously.
Q. 2. The plants grow fastest if we add fertilisers in the soil, but if we add manure, 
plants grow but at a slower rate. Give reason.
Answer: Fertilizers are chemical compounds which provide immediate a particular 
nutrient to plants and help them grow faster. Whereas manure is low in nutrient content 
and it takes a longer time to release nutrients in the soil. As the result plants grow 
slowly. But the use of manure improves soil textures, as well as its water, retaining 
capacity. It replenishes the soil with all the nutrients.
Q. 3. If excess fertilizer is added to the soil, what can happen?
Answer: By the use of fertilizers, farmers get a better yield of crops. But excessive use 
of fertilizers adversely affects the soil fertility. Continuous use of fertilizers makes the


soil less fertile. Fertilisers also cause water pollution. Therefore, in order to maintain the 
fertility of the soil, we should use more organic manure or leave the field uncultivated 
(fallow) in between two crops.
Q. 4. Does nitrogen fixation help in nutrient enrichment?
Answer: Nitrogen fixation is a process by which nitrogen present in the atmosphere is 
converted into nitrate. Nitrate is the compound of nitrogen that is used to increase the 
growth rate of the plant.
The leguminous crops like beans and peanuts have Rhizobium bacteria which are 
present in the nodules of the root of the plant is responsible for nitrogen fixation.This 
help in the replenishment of the nitrogen in the soil which provides better growth for 
Rabi crops like wheat.

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