Class 8, Crop Production and Management - Chapter 1, Science - NCERT Answers of Textbook Exercise

 

CBSE Class 8, ScienceCrop Production and Management

NCERT Answers of Science Chapter 1 Exercise Questions

Question.1: Select the correct word from the following list and fill in the blanks:
a)   The same kind of plants grown and cultivated on a large scale at a place is called _______.
b)  The first step before growing crops is ______of the soil.
c)   Damaged seeds would _____ on top of the water.
d)  For growing of crop, sufficient sunlight and ______and _____ from the soil are essential.
Answer: (a) Crop (b) Preparation (c) Float (d) Water, Nutrients.
Question.2: Match items in column ‘A’ with those in column ‘B’:
(A)
(B)
   i.    Kharif crops
 ii.    Rabi Crops
iii.    Chemical Fertilizers
iv.    Organic Manure
a)   Food for cattle.
b)  Urea and super phosphate.
c)   Animal excreta, cow dung, urine & plant-waste.
d)  Wheat, gram, pea.
e)   Paddy and maize.

Answer: (i)-e (ii)-d (iii)-b (iv)-c
Question.3: Give two examples of each: (a) Kharif crop, (b) Rabi crop.
Answer: (a) Paddy and maize (b) Wheat and gram.
Question.4: Write a paragraph in your own words on each of the following:
a)   Preparation of soil
b)  Sowing
c)   Weeding
d)  Threshing
Answer:
(a)  Preparation of Soil
The preparation of soil is the first step before growing a crop. It includes the process of loosening and turning of the soil called Tilling or Ploughing. It is done by using ploughs, which are pulled by bulls. Tractor driven cultivators are also used to till the soil. Tilling of the soils is important for following reasons:-
                    (i)      This allows the roots to penetrate deep into the soil.
                   (ii)      This allows the root to breathe easily.
          (iii)   The loosened soil helps in the growth of earthworms and microbes which further turn and loosen the soil and also help in adding humus to it.
            (iv)   This process brings the nutrient rich soil to the top so that plants can use these nutrients.
(b)  Sowing
Sowing is the most important part of the crop production in which seeds are implanted in the prepared soil. Before sowing only clean, healthy, good-variety and high yield seeds are segregated and sowed in the fields. In the traditional method of sowing seeds, a long pipe is used which has a funnel at its one end and the other end pierce into the soil through which seeds are placed. Now a days a machine or a tool known as seed drill is also used for sowing with the help of tractors. A seed drill saves time & labour. While sowing the seeds care should be taken to maintain proper distance and depth between the seeds to prevent damage of the seeds caused by birds and also to prevent overcrowding of the plants.  
(c)   Weeding
Unwanted plants growing along the crops are called weeds. The process of removal of weeds is called weeding. Weeding is necessary since these weeds absorb the water, nutrients, space and light meant for the crop plants. Weeding can be done manually with a ‘khurpi’ or mechanically with the help of a ‘seed drill’ or even using certain chemical called ‘Weedicides’. The best period for weeding is during their vegetative phase before flowering or bearing seeds.
(d)    Threshing
When the crops are harvested they are cut along with the stalks. They are then, separated and the grains are removed. This process of separation of grains from the chaff is called ‘Threshing’. This whole process is carried out with a machine called ‘Combine’ which is in fact a combined harvester & thresher.
Question.5: Explain how fertilizers are different from manure. 
Answer: The differences between fertilizers and manures are as follows: 
  1. Fertilizers are chemical substances, while the manures are the organic substances (decay of plants & animal wastes).
  2. Fertilizers are prepared in the factories, while the manures are prepared in fields. 
  3. Fertilizers don’t provide any humus to soil, while manures provide a lot of humus.
  4. Fertilizers are rich in plant nutrients like- Nitrogen, Phosphorus & Potassium but manures are less rich in plant nutrients. 
  5. There are certain advantages of adding manure like-
a)   It enhances the water holding capacity of the soil,
b)  It makes soil porous due to which exchange of gases becomes easy.
c)   It improves the texture of soil and also increases the number of friendly microbes.
Question.6: What is irrigation? Describe two methods of irrigation which conserve water.
Answer: Watering the crops in the fields is called ‘irrigation’. Irrigation is done at different intervals. Irrigation should be done in a way in which water does not get wasted. Different sources of irrigation are like- wells, tube-wells, ponds, rivers. Two such methods which conserve water are:
     (i)  Sprinklers: Sprinklers work like fountains. Long perpendicular pipes having rotating nozzles on the top are joined to the main pipe lines at regular distances. When water is supplied, it comes out of these rotating nozzles which sprinkle water in all directions. Limited outflow of water, controls wastage of water. This method is more suitable for uneven and sandy soil.
(ii) Drip System: This system allows the water to flow drop by drop at the roots of the plants. It contains a main pipe which has further lateral pipes containing small nozzles for the outflow of the water. Nozzles are such placed that they throw water at the roots of the plants, which saves water from flowing around uselessly. This technique is best suited for watering fruit plants, gardens and trees where availability of water is poor.
Question.7: If wheat is sown in kharif season, what would happen? Discuss. 
Answer: If wheat is grown in kharif season, they would not grow as they don’t need much water to grow. The seeds would get destroyed in excess water due to rainy season.
Question.8: Explain how soils get affected by the continuous plantation of crops in a field.
Answer: Continuous plantation of crops drains off the nutrients of the soil. It leaves the land unfertile and unable to bear crop. It does not give any time to the soil to replenish the absorbed nutrients by the crops, thus unable to sustain any further healthy and good crop.
Question.9: What are weeds? How can we control them? 
Answer: Weeds are the unwanted plants growing along crops. They share the nutrients meant for plants and thus are harmful for crop. We can control weeds with the help of chemicals Weedicides. The removal of weeds is called weeding. They are either, removed manually or by chemicals.
Manually this can be done with the help of Khurpi or Seed-drill. Weedicides are sprayed in the fields to kill the unwanted plants. These weedicides do not affect the main crop. Weeds are removed or killed during their vegetative phase before flowering or bearing of seeds.   

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