NCERT 8th Class (CBSE) Science: Crop Production

Question: Name three natural methods of adding nutrients to soil. Answer: The three natural methods of adding nutrients to soil are: Field fallow, Crop rotation and Mixed cropping. Question: What are weeds? Answer: The unwanted plants that grow along with the crops and share nutrients are called weeds. Weeds decrease the crop yield as they compete with crops for water, nutrients and sunlight and limit their growth. Question: Why should grains be dried before storage? Answer: Grains should be dried before storage to remove moisture. This excess moisture helps growth of microbes that may destroy the grains. Question: Why does the government usually maintain a buffer stock of grains? Answer: The government usually maintains a buffer stock of grains to avoid shortage of grains during natural disaster. Question: What is hybridization? Answer: Hybridization is a technique to develop new varieties of crops by cross breeding two different varieties. Question: List the steps involved in the nitrogen cycle. Answer: The steps involved in the nitrogen cycle are as follows: Nitrogen fixation Nitrogen assimilation Ammonification Nitrification Denitrification Question: What do you mean by nitrogen fixation? Answer: Nitrogen fixation is the process of converting free atmospheric nitrogen gas into nitrogen compounds nitrites and nitrates. Question: What is nitrogen assimilation? Answer: Nitrogen assimilation is the process by which inorganic nitrogen compounds are converted into organic compounds such as proteins that become a part of living beings. Question: What enables leguminous plants to fix nitrogen? Answer: The nitrogen fixing bacterium Rhizobium live in the root nodules of leguminous plants like peas and beans. These bacteria can fix atmospheric nitrogen into nitrates. Thus, enables them to fix nitrogen. Question: What is animal husbandry? Answer: The breeding, feeding and caring of domestic animals for food and other purposes is called animal husbandry. Question: Distinguish between kharif and rabi crops, giving two examples of each. Answer: The difference is as follows: Question: List the steps involved in crop production, in sequential order. Answer: The steps involved in crop production are as follows: Preparation of soil - Selection of seed and sowing Manuring - Irrigation - weeding Protection from pests and diseases Harvesting, threshing and winnowing Storage Question: Why is it important to plant seeds at the correct distances from each other? Answer: Seeds should be planted at a proper distance from each other so that they cannot compete for water, nutrients and sunlight. If they are too far apart, there is wastage of field space. Question: Why do farmers normally use a mixture of manures and fertilizers in their fields? Answer: Farmers normally use a mixture of manure and fertilizers in their fields to increase the yield and production of crops. Manure is good for plants as it provides them with organic nutrients but it lacks some important nutrients like nitrogen, phosphorous and potassium. So, along with manure, farmers also use fertilizers such as NPK fertilizers that provide nitrogen, phosphorous and potassium. Question: What method of irrigation will you use if you live in a dry area with shortage of water? Explain the method. Answer: Drip irrigation is the method of irrigation useful for dry areas which have a shortage of water. In this method, water is. Water is allowed to fall drop by drop from a pipe placed near the roots of plant. Question: What is water logging? How does it harm the crops? How can it be prevented? Answer: When an excess of water is supplied to the field it is called water logging. As a result of this, the air supply to the roots reduces and in extreme cases, gets totally cut off. This results in the retarded growth of plants. Water logging can be prevented by supplying just the adequate amount of water to the field using a proper drainage system. Question: Discuss two methods of weeding in which poisonous chemicals are not used. Answer: The two methods of weeding in which chemicals are not used are: Manual method: Weeds are pulled out by hand or uprooted using a trowel or a harrow. Introducing Insect: Insects that feed upon only specific weeds are used control weeds. Question: Differentiate between insecticides, rodenticides and fungicides. Which of these are pesticides? Answer: Insecticides are chemicals used to kill insects like locusts. Rodenticides are chemicals used to kill rodents like rats and Fungicides are chemicals used to destroy fungi. Insects, rodents and fungi are pests. So insecticides, rodenticides and fungicides are all pesticides. Question: Discuss with an example how hybridization is used for developing new varieties of crops with desired characteristics. Answer: Hybridization method of obtaining new variety of desirable traits by cross breeding two different varieties of crops for example if two varieties of crops, one with high yield and other with disease resistance, can be crossbred to obtain a variety that has both the traits, i.e., high yield and disease resistance. Question: Differentiate between nitrification and denitrification. Answer: Nitrification is the process of conversion of ammonia into nitrates. It is carried out by nitrifying bacteria. Denitrification is the process of conversion of nitrates into free nitrogen gas. It is carried out by denitrifying bacteria. Question: What are the advantages of ploughing the soil before sowing seeds? Answer: The process of loosening and turning the soil is called tilling or ploughing. This has the following advantages: Loose soil has a lot of air trapped in it, which is used by the roots to breathe easily. Loose soil allows the roots to penetrate deeper, thus securing the plant more firmly. Loose soil helps the growth of earthworms and microbes in the soil. They provide nutrients to the soil and aid in further loosening of the soil. Turning and loosening of soil brings nutrient-rich soil to the top. Plants can then absorb these nutrients more efficiently. Loose soil mixes more uniformly with fertilizers. Question: What precautions must be kept in mind while sowing seeds in a field? Answer: While sowing, the following points need to be kept in mind: Seeds should be of good quality, healthy and free from diseases. They must be planted at the proper depth in the soil. If planted deep in the soil, they cannot respire, and their shoots may not be able to push through the soil. If planted on the surface, they will be eaten by the birds. Seeds require water for germination. The soil should, therefore, have water in it. However, if there is too much water, seeds will not germinate properly. Seeds should be sown at proper distances. If they are too close they will not get enough water, sunlight and nutrients. If they are too far apart, there is wastage of field space. Question: Discuss two natural methods of manuring. Answer: Two natural methods of manuring are: Manures: Manures are organic substances obtained from dead plants and animal wastes. Green manure is made from crops grown specially to be ploughed into the soil while still green, i.e. legumes, rye grass, fenugreek, etc., to improve the fertility of the soil. Animal manure consists of animal wastes. Compost is a manure obtained by the decomposition of dead plants and animal waste. Compost is made by burying all available organic materials in a pit with alternating layers of soil, and leaving it to rot. Bacteria and fungi in the layers of soil speed up the decomposition. Compost is rich in organic nutrients but not in some important nutrients like nitrogen, phosphorus and potassium. Question: Draw a labelled diagram to illustrate the nitrogen cycle. Answer: Question: Which method, according to you, can bring about the maximum increase in crop produce in our country in future? a. increasing land under cultivation, b. using more manures and fertilizers, c. less wastage in storage, d. using better varieties of crop plants Answer: (d) using better varieties of crop plants. Better varieties of crop plants will result in increased production as they give higher yield as well as high resistance to diseases. Question: What do you think are the drawbacks of seeds being unevenly distributed in a field while sowing? Answer: The drawbacks of uneven distribution of seeds in a field, while sowing, are: They will compete for water, nutrients and sunlight that result limited growth. If they are sown far apart, it will result in the wastage of field area. If seeds are not sown at the proper depth and covered by soil, they may be eaten up by birds. Question: Do you expect to find fully-grown crop plants in a nursery? Why? Why not? Answer: We won't find fully grown crop plants in a nursery like rice, tomato, onion, etc. because they are transferred to the fields from nurseries in their seedling stage. Question: Crop rotation is practised by farmers so that they have different products to sell in the market in every season. Do you agree? Give reasons. Answer: No, farmers adopt crop rotation to maintain the fertility of the soil. For examples , wheat and rice use large amount of nitrogen from soil therefore legumes plants are grown next to the wheat or rice to replenish nitrogen naturally in field. Question: I have grown a few wheat plants in my garden because I like the plants. Am I growing a wheat crop? Give reasons. Answer: No. Growing a few plants in a garden is not crop production. Crop production is the practice of growing wheat on a large scale in a field to cultivate grains. Question: It is observed that melon fruits growing in the fields sometimes crack, exposing the contents inside. What do you think can be the reason? (HINT: This generally happens in fields where drainage is not proper.) Answer: Melons growing in waterlogged fields with poor drainage tend to absorb more water than they require. Melons cannot hold this excess water, therefore, they crack. Question: Write a paragraph in your own words on each of the following: Preparation of soil, Sowing, Weeding, Threshing. Answer: Preparation of soil: The first step of cultivation is preparation of soil. This is done by loosening and turning. A plough is used for this purpose. If the soil becomes too hard then farmer may resort to watering the soil before ploughing. Traditionally, animal-drawn ploughs have been used by farmers. Now-a-days, tractor-drawn ploughs are used for this purpose. A tractor helps in saving time and labour. Sowing: Seeds are sown in the field after ploughing. A farmer needs to separate damaged seeds from good seeds. The seeds should be sown at proper gaps and at proper depth. Proper gap between seeds and proper depth in soil ensures adequate sunlight, moisture, air and nutrients to the growing plants. Weeding: Removal of weeds is called weeding. Weeding is usually done manually or by using a trowel. Weeds are also removed during ploughing. Weedicides are the chemicals which destroy weeds. 2, 4 – D is an example of weedicide. Weedicides are sprayed before flowering and seeding in weeds. A farmer needs to take precautions to prevent any harm from weedicide. Threshing: Separation of grains from harvested crop is called threshing. Threshing is done by threshing machine or by cattle. Cattle are tied in a series around a pole. Harvested crop is spread around the pole. Animals are made to trample the harvested crop. It helps in separating the grains from the harvested crop. Question: Explain how fertilizers are different from manure. Answer: The difference is as follows: Question: What is irrigation? Describe two methods of irrigation which conserve water. Answer: Plants need plenty of water to grow. Farmers need to supply water to crops at regular intervals. This practice is called irrigation. Two methods of irrigation which conserve water are as follows: Sprinkler System: The sprinkler system is composed of a series of pipelines. Vertical sprinklers are fitted at suitable gaps on the pipes. Water is pushed through the pipes with the help of a pump. The nozzle of the sprinkler keeps on rotating. It results in a jet of water being sprinkled on plants. Sprinkler system is ideal for irrigation on uneven land. Drip Irrigation: In this system, pipes are laid near the base and along the queue of plants. The pipes have small holes at frequent gaps. The holes facilitate gradual dripping of water on the base of plants. This method is ideal for areas which are suffering from shortage of water. Question: If wheat is sown in the kharif season, what would happen? Discuss. Answer: Crop of wheat requires moderate temperature, moderate amount of water and a long period of frost-free days. If wheat is grown in kharif season it may not grow properly because of very high temperature. Some of the plants may also get damaged due to flooding. This will result in poor yield. Question: Explain how soil gets affected by the continuous plantation of crops in a field. Answer: We know that plants take nutrients from soil and thus exhaust the soil of most of the nutrients with passage of time. Thus, continuous plantation of crops in the field results in loss of fertility for the soil. The soil may become infertile in the long run. Question: What are weeds? How can we control them? Answer: Any unwanted plant which grows along with crops is called weed. Removal of weeds is called weeding. Weeding is usually done manually or by using a trowel. Weeds are also removed during ploughing. Weedicides are the chemicals which destroy weeds. Weedicides are sprayed before flowering and seeding in weeds. Question: Explain the structure of a plough. Answer: A plough is composed of ploughshare and ploughshaft. The ploughshare is triangular in shape and is made of iron. The ploughshaft is made of wood and is very long. It is harnessed to a pair of bullocks or other cattle with the help of a beam. Question: Explain the structure of traditional seed drill. Answer: The traditional seed drill is composed of a funnel with a long and pointed neck. It is attached to the ploughshaft. Seeds are kept in the funnel and they drop slowly through the neck, while the field is being tilled. The pointed neck of the seed drill pierces the soil and seed goes deep into the soil. Question: What is the significance of ploughing? Answer: Significance of Ploughing: This allows the roots to penetrate deep into the soil. Loose soil allows the root tips to breathe easily when they go deep into the soil. It allows proper mixing of nutrients from humus into the soil. Loosening of soil brings nutrients and minerals to the top and thus plants are able to utilize these minerals. Question: Write a brief note on fertilizers. Answer: Fertilizers are human made chemical substances that contain one or more nutrients essential for plant growth. They are made in factories. The most widely used fertilizer are NPK fertilizers that are rich in nitogen (N), phosphorous (P) and potassium (K) salts. They are easy to store and handle. Since they are soluble in water, they are directly absorbed by plants and greatly increase crop yields. Some other examples of fertilizers are urea, ammonium sulphate, super phosphate, potash etc.. However, if overused, fertilizers harm the soil by making it porous. Excess fertilizers get washed into water bodies and harm aquatic animals. Question: What are the advantages of fertilizers? Answer: Advantages of Fertilizers: Fertilizers give quicker results compared to manure. Use of fertilizers has helped farmers in significantly improving farm yield. Question: Write a short note on storage of crops. Answer: Proper storage of harvested crop is important to prevent damage from moisture and pests. Grains are sun dried before being stored. Grains are stored in silos. Silos can be of varying heights; ranging from one meter to several meters. Fruits and vegetables are stored in cold storage. Suitable pesticides are used while storing grains. Neem leaves are also used as pesticides. Question: Write a short note on crop rotation. Answer: In this method, a legume crop is sown between two successive cereal crops. Legume plants harbor rhizobium bacteria in their root nodules. These bacteria help the plants in nitrogen fixation in soil. Thus, growing a legume crop helps in replenishment of nutrients in soil. Question: What are the advantages of manure? Answer: Advantages of Manure: Manure increases nutrients in soil. It improved soil texture. It improves water retaining capacity of soil. It is free of any toxic material and thus is environment friendly. Question: Explain the structure and working of hoe. Answer: This is used for leveling the soil and for removing weeds. This is made of iron or wood. It is a long beam with a handle. A sharp blade is fixed on one end. This is usually pulled by animals. A hoe is used for leveling the field.

Class Notes NCERT Solutions for CBSE Students

NCERT 8th Class (CBSE) Science: Crop Production

Question: Name three natural methods of adding nutrients to soil.

Question: What are weeds?

Question: Why should grains be dried before storage?

Question: Why does the government usually maintain a buffer stock of grains?

Question: What is hybridization?

Question: List the steps involved in the nitrogen cycle.

Question: What do you mean by nitrogen fixation?

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