Crops | Science Class 9 PDF Download

Crops
Plants of same kind which are grown and cultivated at one place on a large scale are known as crops. Different types of crops require different climatic conditions like temperature, humidity and photoperiods. Crops are divided into two groups on the basis of growing season.

Kharif crops : These crops are sown in the months of June/July and harvested in September/October every year.
eg- Paddy, maize, sugarcane, sorghum, pearl millet.
Rabi crops : These crops are sown in the months of October/November and harvested in March/April every year.
eg- Wheat, oat, barley and pea.
Agriculture : Word agriculture has come from two Latin words, ager meaning field or soil : culture meaning cultivation. Agriculture or farming is the cultivation of the soil. It includes growing of plant crops and rearing of animals.

It is an applied biological science which deals with the production of plants and raising of livestock for human use.

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Modern agriculture :_ Modern agriculture is a combined effort of art, science and technology to provide food, cloth and shelter to increasing human population. To improve the efficiency of the agriculture process and increase output following steps are taken:

1. Highly efficient tools and machines are made and used.
2. Building of dams and canals for irrigation.
3. Development of pest resistant and high yielding variety.
4. Use of fertilizers and pesticides for nutrition and protection of crop respectively.

Sustainable agriculture : The practice of farming and production of maximum agriculture yield through management of natural resources without disturbing the environment is known as sustainable agriculture.

In India there has been a four times increase in the production of food grains from 1960 to 2004 with only 25% increase in the cultivable land area.

The major groups of activities for improving crop yields can be classified as :

(i) Crop variety improvement (the choice of seed for planting).

(ii) Crop production improvement (the nurturing of the crop plant).

(iii) Crop protection management (the protection of the growing and harvested crops from loss)

1. Crop variety improvement

The desirable superior character in a variety can be incorporated through various methods of genetic
 improvement of crops.

Plant breeding :- Plant breeding is the science and art of improving the heredity of plants in relation to
 their economic use. The various methods of breeding are as follow :

Introduction :- It is the oldest method of crop improvement.

Hybridization : The process of cross breeding between two geneticaly dissimilar individuals is called hybridization. This process helps to produce hybrid variety with desirable characteristics. In order to obtain an improved variety. Following steps should be taken.

Choice of Parents : Select two varieties of crop plants, each of which has at least one desirable quality, such of high yield or resistance to disease.

Cross breeding :- Pollen grains of plants of one variety are dusted over the stigmas of plants of the other
 variety and vice-versa. It produces a new variety which has good characteristics of both the parents.

Hybridization may be of three types :-

(a) Intervarietal (between two different varieties of same species).

(b) Interspecific (between two different species of the same genera).

(c) Intergeneric (between two different genera).

Genetic engineering :- Transfer of one or more genes (DNA fragments) from one plant to another. The plant in which the foreign gene has been introduced is called transgenic plant or genetically modified plant.Bt Cotton is a genetically modified crop which carries bacterial genes that protect the crop plants from insects.

Objectives of plant breeding :-

Higher yield :- To increase the productivity of crop per acre. The main aim of crop variety improvement is to obtain higher yield e.g. grains, tubers. Such a variety is called HYV or high yielding variety.

Need of Higher Crop Yield :- There is an urgent need to continuously increase crop yield because of
 (i) Rising human population. (ii) Rising animal population.

(iii) Increasing realisation about intake of proper diet. (iv) Limited cropping area.

Better quality :- Quality consideration such as baking quality, protein quality, oil quality and preserving quality of crop products vary from crop to crop.

Biotic and abiotic resistance :- Crops production can go down due to biotic (microbes, insects, rodents) and abiotic stresses (Flood, drought, frost). Varieties resistant to these stresses can improve crop production.

Change in maturity duration :- The shorter duration of the crop from sowing to harvesting, the more economical is the variety.

(i) It helps the farmers in raising multiple rounds of crops in a year from the same field.
(ii) Cost of production is reduced.

Wider adaptability :- Developing varieties for wider adaptability will help in stabilising the crop production under different environmental conditions.

Desirable agronomic characteristic :- Developing varieties of desired agronomic characters helps to give higher productivity. To achieve high productivity, the food crops (cereals) should be dwarf (short height), so that they consume less nutrients, become stronger and withstand strong winds (prevent lodging). The fodder crops should be tall and should have profuse branching.

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Green Revolution :- The great increase, in the yield of food grains (especially the wheat crop), as during the 1970s, is called green revolution.

Green revolution has made the country self-sufficient in food ; increased the buffer stocks of food grains and improved the economic conditions of farmers as well as has provided employment opportunities to large number of people.

2. Crop production improvement

India is an agriculture based country. Different types of farming practices are being carried out by different types of farmers. They depend upon size of the land holding, education and finanical conditions of the farmers. The production practies include "no cost" production, "low cost" production and "high cost" production. High cost production is based on improved high yielding varieties, improved farming practices, modern technology, latest agricultural machines and implements. Crop production management has three components, (A) nutrient management (B) irrigation (C) cropping pattern.

(A) Classification of plant nutrients :

There are 16 essential elements for growth and development of plants. They are classify into two grops

Macronutrients :- The essential element utilised by plants relatively in large quantities are called major nutrients or macronutrients.

Micronutrients :- The essential element utilised by plants relatively in small quantities or traces are called micro nutrients.

Manuring : Farmers have to add manure to the field to replenish the soil with nutrients, the process known as manuring.

Manure : These are organic substances, obtained from the decomposition of plant and animal wastes.

Advantages of manure :

1. It increases the number of friendly microbes.
2. It improves the texture of soil by adding organic matter (humus).
3. It increases soil fertility, water holding capacity and aeration.
4. It reduces soil erosion.
5. It is cheap.

Disadvantage of manure :

1. They have less amount of nutrients as compared to fertilizers.
2. Manures are bulky and not easy to store and transport.

Fertilizers : These are commercially manufactured inorganic salts containing one or more essential plant nutrients like NPK, which are used to increase soil fertility.

Advantages of fertilizers :

1. They are nutrient specific and required in small amounts.
2. They are water soluble and absorbed by the plant easily.
3. They are easy to store and transport.

Disadvantages of fertilizers :

1. Fertilizers can change the soil structure by killing the soil microbes.
2. Fertilizers can change the chemical composition of soil.
3. Accumulation of fertilizers in water bodies causes eutrophication.

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Methods for maintaining soil fertility without use of fertilizers

Field fallow : The practice of leaving the field uncultivated for a season is called field fallow.

Crop rotation : The practice of growing different crops in succession in the same field is called crop rotation.

Biofertilizers : Organisms which enrich the soil nutrients due to their biological activities are called biofertilizers. e.g. Rhizobium bacteria, Nostoc and Anabaena(BGA).

Body of the living organisms is made of proteins. Proteins are the compounds of nitrogen, carbon, oxygen and hydrogen. Air nitrogen is fixed into compounds of nitrogen (Nitrogen oxides solution in water) by certain microorganisms. Microorganisms such as Rhizobium (= Bacillus) bacterium is present in the root nodules of Leguminous plants Bacterium Rhizobium radicicola is capable of fixing air nitrogen. Fixation of nitrogen enriches soil in a natural way.

Nitrogen fixation is the process of combining oxygen with nitrogen to form nitrogen compounds such as nitrites (NO₂) and nitrates (NO₃).

Blue green algae are common along drains, wet places and flooded paddy fields.Anabena, Oscillatoria, Nostoc and Gleocapsa are common examples of blue green algae.

Root nodules : Roots of leguminous plants bear root nodules. Root nodules house Rhizobium, a nitrogen fixing bacteria. Nitrogen fixed by the bacterium is supplied as additional nitrogenous nutrition to the leguminous plant (host). In turn, the host plant provides shelter and carbohydrate food to the bacterium. Thus, the bacterium and the leguminous root nodules are living together for mutual benefit. This process in which two organisms live together for mutual benefit is called symbiosis.

1. They require more human labour and human efforts.
2. They are less efficient so water is wasted in large quantity.
3. They are not useful for poor water regions.

Nowadays the following modern ways of irrigation are used:

(i) Sprinkler system :_

• In this system the perpendicular pipes having rotating nozzels on top, are joined to main pipe line at regular intervals.
• It spreads water uniformly over crop plants and field.
• This method is useful for sandy soil and uneven land.
• It is an efficient system in the canal irrigated area of Haryana and Rajasthan.

 (ii) Drip system or trickle irrigation :

• It involves the use of pipes fitted with small tubes called emitters. The pipes are laid over or under the soil and emitters release water drop by drop around the roots of the plants.
• In this method water is not wasted at all.
• This method is a boon in poor water regions.
• This is the best irrigation technique for fruit crops, garden and trees.

 Advantage of irrigation :_

• Supply of essential elementsIrrigation water supplies two essential elements to crops i.e. hydrogen and oxygen.
• Germination of seedsMoisture available in soil leads to germination of seeds.
• GrowthGrowth of roots occur inside the soil by availability of water in soil.
• Absorption of nutrientsWater made available to field by the process of irrigation helps in absorption of nutrients by plants from the soil.