CBSE Class VIII Science Preparation

•   Agriculture: The applied branch of biology which deals with cultivation of plants and rearing of animals is called agriculture. Generally, the art or practice of cultivating land is referred as agriculture. The branch of agriculture which deals with food, health and management of animals is known as animal husbandry.

•   Crop: When plants of the same kind are grown and cultivated at one place on a large scale is called as a crop.

•   Crops are also classified on the basis of the seasons as given below:

     ▸   Kharif Crops: The crops which are grown during the monsoon (rainy) season (June-September) are called kharif crops. For example, maize, millet (bajra) and cotton crops. Seeds of these crops are sown in the beginning of the monsoon season. After maturation, these crops are harvested at the end of the monsoon season (Oct.-Nov.).

     ▸   Rabi Crops: Crops which are grown during the winter season (October-March) are called rabi crops. For example, wheat, gram and mustard. Seeds of these crops are sown in the beginning of the winter season. After maturation of crops, they are harvested at the end of the winter season (April-May).

•   Agricultural Practices: All activities which farmers do for the cultivation of plants are called agricultural practices.
     For doing various activities, a farmer needs different types of tools. These tools which are involved in cultivation of plants are called agricultural implements. Farmers perform agricultural practices in a sequence.

•   Various Agricultural Practices:

          (i)  Preparation of soil

          (ii)  Sowing

          (iii)  Adding manure and fertilizers

          (iv)  Irrigation

          (v)  Protection from weeds

          (vi)  Harvesting

          (vii)  Storage.

•   Agricultural Implements:

     ▸   Plough

     ▸   Hoe

     ▸   Cultivator

     ▸   Seed drill

•   Implements used for traditional ways of Irrigation:

     ▸(a) Moat (b) Dhekli

     (c) Rahat

     (d) Chain pump and

     (e) Motor pumps

•   Basic Practices of Crop Production

     ▸   Preparation of Soil: Before sowing the crop seeds, the soil of fields is loosened and overturned.
            This process is called ploughing or tilling. Ploughing causes ventilation of soil and makes it suitable for the growth of small organisms living in it.

     ▸   Plough: A large farming implement with one or more blades fixed in a frame, used to turn over and cut furrows in soil, is called plough. Plough may be made of only wood, wood and iron, and of iron only (Fig. 1.1).

     ▸   Ploughshare: The main cutting blade of a plough.

     ▸   Hoe: A tool which is used for removing weeds and for loosening the soil.

     ▸   Cultivator: Nowadays ploughing is done by a tractor driven cultivator. The use of cultivator saves labour and time (Fig. 1.2).

     ▸   Sowing of Seeds: For sowing, farmers obtain certified seeds from State Agriculture Department and Seed Corporation. Sometimes, farmers also select seeds from their own crop. For selection of seeds of most of the crops, seeds are put into a bucket of water. The seeds which float on water are rejected. These seeds are defective. The seeds which remain submerged in water are selected for sowing. The selected seeds are treated with chemicals such as agrosan or ceresan. This chemical treatment protects seedling from seed-borne diseases. Seeds are sown either by hand-broadcasting (spreading) or by seed drills (Fig. 1.3). A type of seed drill, commonly used, is a long iron pipe having a funnel at the top. It is tied at the back of the plough [Fig. 1.4(a)].
            A farmer does ploughing and simultaneously releases seeds from the funnel. Seeds thus released pass through iron pipe to the soil furrows which are formed by the plough.

     ▸   Adding Manure and Fertilisers: Like other plants, crop plants also obtain their mineral nutrients from the soil. Continuous growing of crop in the field causes deficiency of mineral nutrients in the soil. So, the manure is added to the soil to make up the deficiency of mineral nutrients. This process is called manuring. Manure is prepared from cow dung, urine and other wastes.
            Sometimes, soil becomes deficient in a particular mineral nutrients. This happens when same crop is grown in the same field year after year. For example, a particular crop takes more phosphate. If this crop is grown in a field every year, the soil will become deficient in phosphorus nutrient. This type of deficiency of a particular nutrient is made up by adding chemical substances called fertilisers. For example: urea, super phosphate and NPK (Nitrogen, Phosphorus, Potassium).

     ▸   Irrigation: The supply of water to crops at different intervals is called irrigation. The time and frequency of irrigation varies from crop to crop, soil to soil and season to season.

•   Methods of Irrigation

     ▸   Traditional methods:

          — Moat (pulley-system)

          — Chain pump

          — Dhekli — Rahat

     ▸   Modern methods:

          — Sprinkler system

          — Drip system

•   Protection from Weed
     The unwanted plants in the fields are called weeds. Seeds of these weeds spread through the agencies like air, water, birds and other animals. Weeds share water, sunlight, space, nutrients with the crop plants. Thus they compete with the crop plants. Therefore, their removal is necessary. Otherwise, crop plants do not get sufficient space, water, sunlight and nutrient to grow healthier. Weeds are weeded out either by hand or with the help of an implement called harrow. Nowadays, for checking the growth of weeds, certain chemicals are used. These chemicals are called weedicides, such as 2, 4-D.

•   Harvesting and Threshing: When crops pet matured, they usually turn yellow or golden or brown. This is the time when crops should be cut. Cutting of crops is known as harvesting. Harvesting is either done manually by a sickle or by a machine called harvester. Harvested crop is further dried and then animals such as bullocks, buffaloes, camels are made to walk over it. The grains are separated from chaff with the help of wind (winnowing) (Fig. 1.6). The whole process of separation of the grains from the harvested crop is known as threshing.
     Big farmers use huge machines known as combines which do both harvesting and threshing.

•   Special festivals associated with the harvest seasons are: Pongal, Baishakhi, Holi, Diwali, Nabanya and Bihu.

     ▸   Storage: Grains obtained by threshing are dried in the open. The dried grains are stored in gunny bags, and placed in properly ventilated cemented halls, known as godowns. Farmers keep dried grains in jute bags or metallic bins or mud bins. Large scale storage of grains is done in silos (Fig. 1.7) and granaries (Fig. 1.8). For storing large quantities of grains in big godowns, specific chemical treatments are used to protect them from pests and microorganisms.

•   Animal Husbandary: Food is also obtained from animals for which animals are reared and provided with proper food, shelter and care. When done on a large scale, it is called animal husbandry.

1.  Watering the crops is called:

      (a)   sowing

(b)   manuring

(c)   tilling

(d)   irrigation

2.  Weeds are the:

      (a)   main crop plants

(b)   insects and pests

(c)   unwanted plants growing along the crop

(d)   chemical substances

3.  Combines are used for:

      (a)   sowing of seeds

(b)   harvesting the crops

      (c)   threshing

(d)   harvesting and threshing both.

4.  Separating grains from chaff is called:

      (a)   winnowing

(b)   threshing

(c)   fallow

(d)   harvesting.

5.  Weedicides are used to destroy:

      (a)   insects

(b)   weeds

(c)   pests

(d)   none of these.

6.  Kharif crops are sown in

      (a)   March, April

(b)   May, June

(c)   October, November

(d)   Any time.

7.  Wheat and gram belong to

      (a)   Rabi crops

(b)   Kharif crops

(c)   Both of these

(d)   None of these.

8.  Examples of kharif crops are

      (a)   Wheat and maize

(b)   Gram and maize

(c)   Paddy and maize

(d)   All of these.

9.  2-4D is a

      (a)   Pesticides

(b)   Insecticides

(c)   Fungicides

(d)   Weedicides.

10.  Seed drill is used to

         (a)   sow the seeds

(b)   remove the weeds

(c)   remove the pest

(d)   mix manure in the soil.

Q1.  Select the correct word from the following list and fill in the blanks. float, water, crop, nutrients, preparation

          (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 water.

          (d)  For growing a crop, sufficient sunlight,___________and ___________from the soil are essential.

Ans.      (a)  crop      (b)  preparation      (e)  float      (d)  water, nutrients.

Q2.  Match items in Column A with those in Column B.

Q3.  Give two examples of each:

          (a)  Kharif crop

          (b)  Rabi crop

Ans.    (a)  Paddy and maize.     (b)  Wheat and gram.

Q.4.  Write a paragraph in your own words on each of the following:

          (a)  Preparation of soil

          (b)  Sowing

          (c)  Wedding

          (d)  Threshing

Ans.    (a)  Preparation of soil: Soil is prepared before sowing the seeds. The soil is loosened to increase the absorption of water and manures. Loosening of soil particles adds humus and nutrients in the soil that increases crop yields. Tilling or loosening the soil is done by ploughs which are pulled by a pair of bulls. Tractor driven cultivators are also used to loosen the soil.

                (b)  Sowing: After preparation of soil it is ready for sowing of seeds. The healthy and clean seeds should be selected. The sowing is done by seed drills or funnel shaped tools. Seed drills are the modern instruments which sow the seeds at proper depth and proper distance.

                (c)  Weeding: The unwanted plants in the crops are called weeds. These weeds absorb the nutrients from the soil. So it is necessary to remove them. Weeds are either removed manually or by mechanical tools. The process of removal of weeds is called weeding. Some chemicals like 2, 4-D are also used to kill the weeds.

                (d)  Threshing: Separation of grains from the chaff is called threshing. When the crop is harvested, it is cut along with the stalks. They are then separated and the grains are removed. Winnowing machine is used to separate grains from chaff.

Q5.  Explain how fertilisers are different from manures.

Ans.       (i)   Manures are organic substances while fertilisers are chemical substances.

                (ii)   Manures are prepared in fields while fertilisers are prepared in factories.

                (iii)  Manures contain all the nutrients while fertilisers are rich in certain nutrients.

                (iv)  Manures provide humus while fertilisers do not provide any humus.

Q6.  What is irrigation�? Describe two methods of irrigation which conserve water.

Ans.    The process of watering the crops is called irrigation.

                   Two methods of irrigation are:

                  (i)   Sprinklers: Sprinklers work as fountains. Long perpendicular pipes have holes at regular distances. When water is supplied, it comes out of these holes and spray water in field. These holes have rotating nozzles which sprinkle water in all directions. They control wastage of water.

                 (ii)   Drip System: This system is used to save water as it allows the water to flow drop by drop at the roots of the plants. It is the best technique for watering fruit plants, gardens and trees. Water is not wasted at all.

Q.7.  If wheat is sown in the kharif season, what would happen? Discuss.

Ans.    Wheat crop does not require much water to grow, so wheat would not grow in kharif season. The seeds would get destroyed in excess water due to rainy season.

Q8.  Explain how soil gets affected by the continuous plantation of crops in a field.

Ans.    If we sow continuously in a field then the lacking of nutrients takes place in the soil. The field becomes unfertile. It does not give any time to soil to replenish the nutrients.

                    Thus the soil is unable to sustain any further healthy and good crop.

Q9.  What are weeds? How can we control them?

Ans.    Weeds are unwanted plants. They grow with crops. They compete for nutrients and water with main crop. So weeds are very harmful. Process of controlling the weed is called weeding. Weeding is done manually by using khurpi and by using mechanical machines. Weeds are also controlled by using some chemical substances like 2, 4-D. These chemicals are called weedicide and used to kill and destroy the weed.

1.  What are the basic practices of crop production?

2.  What are crops? Explain the two crops in detail.

3.  Write a short note on weeding.

4.  Explain how fertilizers are different from manures?

5.  Give examples of two Rabi and two Kharif crops.

6.  Explain modern method of sowing.

7.  What is crop rotation and why is it important?

8.  How are grains stored and protected?

9.  Mention names of any two fertilizers.

10.  Why is it necessary to sow seeds at appropriate depth?

1.  Weeds compete with crop plants for_____.                        (1)

2.  Soil can be loosened with the help of a :                            (1)

3.  Growing different types of crops in pre-planned succession is known as :            (1)

4.  Give two examples of Kharif and Rabi crops.                    (2)

5.  What is weeding?                                                                        (2)

6.  Why can roots of plants breathe easily in loose soil?            (2)

7.  Why do Paddy crops grow in rainy season?                            (3)

8.  Describe methods of irrigation which conserve water.            (3)

9.  Explain how Fertilizers are different from Manures?            (5)

10.  Write short notes on                                                                            (5)

          •  Weeding

          •  Threshing

          •  Preparation of Soil

          •  Sowing

          •  Affects on soil due to continuous plantation of crops in a field

11.  Give one example of each                                                                (5)

          •  Weed

          •  Plant pest

          •  Organism used in biological control method

          •  Crop that has the natural ability to make soil fertile

          •  Usable form of nitrogen for plant growth.