eChapters

Starters are selected strains of micro-organisms deliberately added to milk during conversion into cheese, dahi, yoghurt and other fermented dairy products to bring about specific changes in the appearance, body, texture and flavour characteristics of the desired final products.

Functions of Starters

The primary function of almost all starter culture is to develop acid in the product. The secondary effects of acid production include coagulation, expulsion of moisture, texture formation and initiation of flavour production. In addition to these, the starters also help in imparting pleasant acid taste, conferring protection against potential pathogens and providing a longer shelf life to the product. These bacteria convert 1% of lactose in milk approximately to lactic acid with very little by-products such as acetic acid, ethanol, CO2 and normally with no substances causing taints and hence leading to a clean and wholesome milk souring.

In India, the collection, transport and distribution of raw milk involves a number of agencies and persons at rural and urban level – village producers, milk collectors, halwais (Sweet-makers), milk vendors, dairies, producer-retailers and wholesale or retail markets.

1. Collection

Usually, the milk collectors approach the small village producers to collect milk and the same is sold directly or indirectly (through agents) to a dairy (milk procurement centres) or halwais or city milk vendors or consumers. The producer – retailers themselves, in some cases, supply the milk to the above said parties. The production of milk in small, scattered holdings in village causes problems during its collection. It involves visits to many villages, some of which are not easily accessible for the purpose.

The Concept of ‘Clean Milk’ Production

Although milk is nature’s most ideal and perfect single food both for the newborn and the mature human beings, the possibility of it being a source of biological and chemical hazards cannot be excluded. In view of the immense dietary importance of milk, the need for production of safe, clean and wholesome milk is emphasized. The term ‘clean milk’ does not mean milk in which all visible dirt is absent or milk from which it has been removed; rather it does denote raw milk from healthy animals, that has been produced and handled under hygienic conditions; that contains only small number of harmless bacteria and that possesses a good keeping quality without being treated by heat. In other words, the unhygienic production of milk may lead to inferior keeping quality as a result of rapid microbial multiplication under favourable storage conditions apart from serving as a potential health hazard. These microorganisms cause the milk to sour quickly, putrefy and develop undesirable flavours, colour defects, ropiness and bitterness. On the other hand, the pathogenic microorganisms, which may gain entry through various sources, may cause many diseases to the consumers.

The sources of contamination of milk on the farm can broadly be categorized as

    a)    Interior of the Udder
    b)    Exterior of the Udder.
The interior reflects the health of the animal, while the exterior depends on the farm condition, equipment, persons, water etc.

a) Interior of the Udder
The animal by itself is one of the most significant contributors of microorganism in milk. The bacteria in the udder usually enter from the teat opening and get distributed internally by their own growth and physical movement. In the normal healthy udder, the types encountered in milk are most predominantly Micrococci, followed by Streptococci, Corynebacterium and others. Most of the bacteria are excreted in fore milk.

The term growth as applied to higher organisms such as animals commonly is concerned with increase in protoplasmic mass and does apply to reproduction or to increase in number. In microbiology the term refers to increase in the number of organisms. Bacteria increase in number by a process of simple binary fission. Each cell increase in size and redivide into two similar cells. Each of the divide cells may in turn divide to become two cells. Each division produces what is termed as new generation of cells, theoretically there are 2,4,8,16,32,64,128,256 cells in the 2,3,4,5,6,7,8,& 9th generation, this is known as logarithmic growth – the population doubles with each successive generation. Under favourable conditions, bacteria produce generation within 15min. Under unfavourable conditions 24 hours of more may be needed for each generation. Generation time for E.coli is 17 to 20 minutes.

Life forms are composed of one of two basic cell types : Eukaryotic or Prokaryotic. Generally, eukaryotic cells are larger and more complex than the prokaryotic cells and possess a membrane-enclosed nucleus; eukaryotic means ‘true nucleus’ (eu=true; karyon = nucleus). All plants, animals, fungi, protozoa and algae are composed of eukaryotic cells. Only the microorganisms classes as bacteria and the archaea are prokaryotic cells. Prokaryotic cells have no nuclear membrane and therefore lack a true nucleus. The latin prefix pro means ‘early’ and in this instance suggests the somewhat primitive nuclear structure found in bacterial cells. Eukaryotic microorganism are sometimes simply referred to as eukaryotes, and the prokaryotic microbes as prokaryotes.

Veterinary public health deals with the contributions of veterinary medicine to public health. It is concerned, in the first instance, with the control and elimination of zoonoses and also with the following areas of activity:
    ·    Food hygiene (production, processing and distribution of foods of animal origin)
    ·    Environmental contamination and degradation by animal wastes and animal products
    ·    Comparative medicine (eg. Studies in animals on naturally appearing cancer, cardiovascular disease, metabolic and other disorders encountered in humans)
    ·    Laboratory animal medicine
    ·    Education and training in VPH and communication with the public
    ·    Reproduction biology
    ·    Aspects of mental and societal health
    ·    Emergency veterinary functions in natural disasters and other catastrophes.

Important by-products from rabbits are meat, wool, planner and skin. It can be made highly profitable if products are wasted because people do not have enough knowledge about their processing.

11.1. Slaughtering and Dressing

    1.    Rabbits are killed by one of two methods. The preferred method is dislocation of the neck. The rabbit is held firmly by the rear legs and head; it is stretched full length. Then with a hard, sharp pull, the head is bent backward to dislocate the neck. The rabbit can also be struck a hard, quick blow to the skull behind the ears. A blunt stick or side of the hand is commonly used to incapacitate the rabbit. Both methods quickly render the rabbit unconscious.

Behaviour have an influence on rabbit housing. Since the domestication of the rabbit is recent in terms of species evolution (200 to 300 generations at most) the behaviour of the domestic rabbit is still much like that of the wild rabbit. The reactions of wild rabbits will often provide explanations for the problems of housing domestic rabbits and suggest ways of solving them. Common behaviours observed in rabbits are:
    1.    Territorial behavior.
    2.    Social behavior.
    3.    Sexual behavior.
    4.    Maternal behavior.
    5.    Feeding behavior.
    6.    Aggressive behavior.

9.1. Handling

Rabbits must be handled very carefully. Although they are generally docile they are apt to struggle when picked up, with potentially harmful consequences. All rabbits are prone to vertebral fractures, and this risk is greatest in hutch rabbits or in those on an unbalanced diet that may have concurrent osteoporosis. It is extremely important to support the back and hindquarters whenever a rabbit is handled.
 
A rabbit should never be picked up by the ears. It can be lifted gently by the scruff of the neck with one hand whilst the other hand supports its bottom (Fig. 9.1), or alternatively lifted with one hand under the chest, and one supporting its hindquarters (Fig. 9.2). The rabbit should be carried against the body to minimize struggling. It is advisable to place the rabbit’s carrying box on the floor so that if it does jump as it is picked up it does not hurt itself. Similarly it is usually easier to return the rabbit to the box on the floor at the end of the examination.

Management of Angora rabbit includes important aspects of breeding, feeding, heeding and disease control.

8.1. Reproduction

Angora rabbits of lighter breeds reach breeding age of 6-7 m, medium rabbits at 7-8m and heavier breeds at 8-10 m. Female Angora rabbits do not have a true oestrus cycle with a definite heat period. They may mate at any time of year. Ovulation in does is induced by mating and occurs about 10 -12 hours later to mounting and copulation with the bucks. No doubt there is no definite heat cycle in Angora rabbits, yet during certain periods breeding does are more receptive to bucks than other times of the year. Some of the signs of such receptive period are restlessness, rubbing of chin on the feeding or watering bowls and vulva may be slightly swollen and purplish red.

Health care and preventive hygiene in rabbits are very important for the productivity of the rabbits and economical viability of a farm.

It is always better to prevent the disease rather than to get an animal treated, which is usually quite expensive. As such it is desirable that the rabbits are checked daily. The health and ailment signs can be recognized from the following things:

6.1. The Production Cycle

As ovulation in does is induced by mating and the females are generally kept in different cages from the males, it is the breeder who determines the reproduction rate of the unit. These rates vary from one or two litters a year under the most extensive management to eight to ten litters in an intensive management system. Does are remated either immediately after kindling (intensive system) or about ten days later (semi-intensive). In the semi-intensive system, the does are first presented to the buck at four and a half months. They are then mated 10 to 12 days after the birth of each litter. Weaning takes place at 30 to 35, or even 37 to 38 days. Extensive systems are characterized by a long delay between kindling and mating, and perhaps even until weaning. For example, the young may be weaned at 56 days and the doe mated after weaning.

5.1. Anatomy of the Genitals

5.1.1. Male reproductive system

Testes in the male are oval-shaped present within the scrotum which remain in communication with the abdominal cavity, where they were at birth. The rabbit is actually able to withdraw its testes when frightened or fighting with other males (Fig. 5.1). The testicles descend at about two months. The short, back-slanting penis points forward when erect.

4.1. Digestive System of Rabbit

The digestive system of rabbit includes:
    A.    The digestive tract 
    B.    Its associated glands
The digestive system breaks down the complex molecules into the simpler one so that it is readily absorbed from gastro intestinal mucosa.
 
A. The digestive tract (gastro intestinal tract/ alimentary canal)

The digestive tract is essentially a tubular structure for the ingestion and digestion of food. In an adult (4 to 4.5 kg) or semi-adult (2.5 to 3 kg) rabbit the total length of the alimentary canal is 4.5 to 5 m. It commences from mouth and terminates in anus. G.I.T is divided into following parts:

The success of rabbit farming depends upon the location and design of the rabbit house. Rabbit is a burrowing animal and has sharp reflexes. It is easily disturbed by any new and sudden noise. The farm should be located in a peaceful environment away from the hustle and bustle of human population.  A good housing facility with adequate arrangement of ventilation is the most important factor in rabbit house.

Domestication of the rabbit is relatively recent and most of today’s breeds have been bred by man in the last 200 to 300 years.

The rabbit has been used as an experimental animal in genetics, reproduction and physiology since the beginning of the century, but it was not until 1950 that the first findings on quantitative genetics were published in Venge’s study of maternal influence on rabbit birth weight.

1.1. History and Origins of Rabbits

The existence of rabbit with human being remained from time immemorial. Romans were the first to domesticate wild rabbits in the 5th century by the monks of the Champagne region in France as a readily available food source. Rabbits were introduced to Britain during the 12th Century, and during the Middle Ages, the breeding and farming of rabbits for meat and fur became widespread throughout Europe. Sources suggest that some women among the Medieval gentry even kept rabbits as pets. The selective breeding of European rabbits meant that distinct breeds arose in different regions, and the origins of many old breeds can be traced back several centuries.

Tools of Public Awareness

The public awareness and awakening can be created among people through various means and ways. In this age of computers and communication, science and technology, information and advertisements there are several quick and effective means of spreading news. The electronic media, the press, education institution, religious, adult education, moral education, spiritual education, religious discourse etc. all are essentially complementary to each other. The governments and the policy makers can only work forwards environmental preservation on political basis. The media, if work passively on pro environmental issues, awareness can be effectively generated among people.

16.1 What is Sustainable Development?

Sustainable development (SD) is a pattern of resource use that aims to meet human needs while preserving the environment so that these needs can be met not only in the present, but also for generations to come (sometimes taught as ELF-Environment, Local people, Future). The term was first  coined by the Brundtland Commission and defined sustainable development as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs” (UN, 1987; Smith and Rees, 1998)

The acts for Environment Protection are :

        The Air (Prevention and Control of Pollution) Act
        The Water (Prevention and Control of Pollution) Act
        The Wildlife Protection Act
        Forest Conservation Act
        Environment Impact Assessment (EIA)
        Citizens Actions and Action Groups
        Public Awareness and Awakening

14.1 What is Education

Education is a systematic attempt towards human learning. All learning is subjective and self related. It is neither literacy nor information. Knowledge can never be learned. Knowledge is the fruit of experience and experience is the sensation of the individual. Individual experience is the internal function and is the function of awareness and understanding. And, one of the processes of knowledge and raising awareness is to be able to identify and clarify our values. Now values in education are essential to help each one of us directly so that we may order our relationships to the environment that lies outside us. Once we are clear about values, we shall be better able to shift and control information of the natural world, make wise choices and decisions, and be creative in our mental processes.

India is home of 16.7 % of the world population living in just 2.4 % of the worlds total land area. The decennial increase in population (1991-2001) has been 18.1 equivalents to the total population of Canada, France and Germany. The population in this century has 1.6 billion by 1960.

12.1 What is Climate Change?
 
The earth receives short-wave radiation from the sun, one-third of which is absorbed by the atmosphere, ocean, ice-land and living organisms. The energy absorbed from solar radiation is balanced, in the long-term, by the outgoing radiation from the earth and atmosphere. While short-wave radiation from the sun can easily pass through the atmosphere, the long-wave radiation emitted by the warm surface of the earth is partially absorbed by trace gases in the atmosphere called greenhouse gases’ (GHGs).

11.1 Global Warming

Definition : Global warming is defined as an increase in the earth’s temperature due to the use of fossil fuels and other industrial processes leading to a build-up of green house gases (CO2, methane, ozone, nitrous oxide, and chlorofluorocarbons) in the atmosphere.

11.2 Who Coined the Term Global Warming?

The principle of global warming was first put fourth by S. Arrhenius in his paper on “the influence of carbonic acid in the air upon the temperature of the ground” in 1869. This concept gained ground in the late 1980s and early 1990s when it was found that the earth’s temperature had warmed over the past century, because of increased carbon dioxide emission.

In November 1992 a document entitled Warning to Humanity was released, signed by 1500 scientists from around the world, including 99 Nobel laureates, and the Director General of the United Nations Educational, Scientific and Cultural Organization (UNESCO). The document stated that “human beings and the natural world are on a collision course,” which “may so alter the living world that it will be unable to sustain life in the manner that we know.”

9.1 What are Natural Disasters?

The natural disasters are earthquakes, floods, droughts, famines, heat waves, cyclones, wild fire, volcanic, aerosols (small particles), and landslides.

9.2 Disaster Management

Both physical solutions and institutional strategies should be developed to manage natural disasters. For flood disaster control the water flow should be checked. Institutional strategies do not rely on physical barriers and include flood plain management, flood and disaster warning systems, education and preparedness programmes.

To a layman, wasteland is a piece of land, which is lying uninhabited or uncultivated. These lands are also commonly perceived to produce much less than their potential. Depleted of the green cover and productivity, such lands are often in a critical condition. Broadly, wastelands may be defined as land where the production of biomass is less than its optimum ‘productivity. Wasteland also refers to lands, which are economically unproductive, ecologically unstable and subject to environmental deterioration.

7.1 What is Pollution?
 
Pollution is a contamination of the environment by man-made substances or energy that has adverse effects on living or non-living matter. In simple terms, pollution can be seen as the wrong substance in the wrong place in the wrong quantities at the wrong time. This implies that harm is caused to the environment if the same substance is present at levels too low.

Types of pollution
Pollution can be categorized according to the medium in which it occurs such as

6.1 Biodiversity

Biodiversity means biological diversity. It measures the variety of the earth’s animal, plant and microbial species; of genetic difference within species and of the ecosystems that support the species in its widest. Biodiversity is virtually synonymous with “life on earth”, this word was coined in 1985. Biodiversity is the degree of variety in nature and not nature itself.

5.1 Concept of Ecosystem

Ecosystem is the basic functional unit in ecology, since it includes both biotic and abiotic environments influencing each other for maintenance of life.

A.G. Tansky in 1935 first proposed the term ecosystem. According to him, it is defined as the system resulting from the integration of all the living and non-living factors of the environment. In a simplest form, an ecosystem can be defined as a self-sustained community of plants and animals existing in its own environment. The term ecosystem is composed of two terms, “eco” means environment and “system” means an interacting and interdependent complex. It is otherwise known as bio system.

In simple words natural resources can be defined as any part of our environment such as land, air, minerals, forest, rangeland, wild life, fish and human beings.

The sum total of all physical, chemical, biological and social factors which compose the surroundings of man is referred to as environment and each component of these surroundings constitute a “resource”.  The natural resources are land, water, air, minerals, forests, rangeland, wild life or even human beings known as natural resource.

The five basic natural resources are energy, matter, space, time and diversity.

3.1 What is environment ?

The word environment is derived from a French word “environne” means to encircle or surround. Environment is defined as the circumstances or conditions that surround an organism or group of organisms. It is also defined as the complex of social or cultural conditions that affect an individual or community. Since humans inhabit the natural world and they build social, cultural and technological world, all constitute important parts of our environment.

Abiotic Environment

The physical or abiotic environment includes all those physical and non-living chemical aspects, which exert an influence on living organisms. The abiotic components are soil, water, air and energy from various sources. These provide both habitation and raw material for the synthesis of organic food.

1.1 Man’s place in Nature

All religions of the world share the view that man is the supreme being among God’s creations. He is the only one among many creatures to enjoy nature’s beauties and bounties. Nature is given to him so as to make responsible and judicious use of it. No religion justifies the most destructive attitude the modern man has developed towards his environment. All religions urge man to treat nature as a God-given gift, stating that God is omnipresent in the manifestations of the nature. It is irreligious for man to expect miracles and exploit the environment. Man must be confronted with the reality that struggle is essential for life rather than “struggle for existence.”

In nature, microbes are found as a mixed population. The types that encounter the most favourable environmental and other growth conditions emerge in abundance while others that find the environment less favourable are fewer in number. However, for any kind of study on them or for their use as a pure species, they have to be separated from other species. The nutritional media or culture media are different for different species. As the medium is specific for certain species, it checks or restricts the growth of other microbes for which it may not be suitable. However, some growth of and contamination by unwanted species may occur.

Biofertilizer is still an unclear term. It can be easily found that biofertilizers are identified as plant extract, composted urban wastes, and various microbial mixtures with unidentified constituents, and chemical fertilizer formulations supplemented with organic compounds. Likewise, the scientific literature has a very open interpretation of the term biofertilizer representing everything from manures to plant extracts.  Quality control of biofertilizers involves several major aspects such as isolation and identification of various strains, screening of the pure isolated strains, fermentation and quality control and finished product.

14.1 Introduction

The green revolution brought amazing consequences in food grain production but with insufficient concern for agricultural sustainability. The availability and affordability of fossil fuel based chemical fertilizers at farm level in India have been ensured only through imports and subsidies which are largely dependent on GDP of the country. Dependence on chemicals for future agricultural needs would result in further loss in soil health, possibilities of water contamination and calculated burden on the fiscal system. Indiscriminate synthetic fertilizer usage has polluted the soil, water basins, destroyed micro-organisms and eco-friendly insects, made the crop more susceptible to diseases and depleted soil fertility at the primary levels as of today (Pindi, 2012). India is an agricultural based country.

Earthworms have been on the earth for over 20 million years. In this time they have faithfully done their part to keep the cycle of life continuously moving. Their purpose is simple but very important. They are nature’s way of recycling organic nutrients from dead tissues back to living organisms. Many have recognized the value of these worms. Ancient civilizations, including Greece and Egypt valued the role earthworms played in soil. The Egyptian Pharaoh, Cleopatra said, “Earthworms are sacred.”

Most trees legumes thrive in tropical regions but N2 fixing non leguminous trees are prevalent in temperature conditions. Callatiam and coworkers from U.K. cultivated Frankia for the first time in 1978 in pure culture. A number of non-leguminous shrubs and trees as Alnus, Myrics, Hippophae, Casuarina and Elaeagnus are nodulated by N₂ fixing Actinomycetes, Frankia with Frankiaceae (Actinomycetes), the only acyinomycete reported to fix nitrogen to date. The so called actinorhizal plants include 7 orders, 8 families, 17 genera and 173 species of dicotyledons plants reported by Gaur, (2010), whereas 200 plants and 23 genera were reported by Diagne et al. (2013). Some of the important non-leguminous families and genera are given in Table 12.1.

11.1 Introduction

Our Country is a fast developing nation for the overall development and has proved that the country which was known for a begging bowl for food grains has turned up towards self-sufficiency and also has excess production to feed the present level of population. From about 50 MT of food grain production in 1950-51, harvest in 2010-11 reached over 241 MT, highest ever along with high production of fruits, vegetables, milk, egg and fish. This increased food production in the country has mainly been achieved through productivity gains, as the net sown area has remained static for the last four decades.

Phosphorus is the second important key element after nitrogen as a mineral nutrient in terms of quantitative plant requirement (Donahue et al., 1990), which is required in optimum amount for proper growth of plants and soil micro-organisms. Being a constituent of ATP, it is involved in various processes such as cell division, energy transduction through photosynthesis and biological oxidations and uptakeof nutrients. The average soil contains 0.05% phosphorus, but only one tenth (1/10) of this is available to plants due to its poor solubility and chemical fixation in soil (Barber, 1984). About 98% of Indian soils have inadequate supply of available phosphorus (Ghosh and Hassan, 1979). A survey of Indian soils showed that out of 363 districts, only 2.2% were high, 51.5% medium and 46.3% were low in phosphorus content (Ghosh, 1982).

BGA belong to a class of prokaryotic photosynthetic microorganisms also known, as cyanobacteria are capable of fixing atmospheric nitrogen aerobically. Most abundantly found in tropical zone, never form fibrous growth and are enveloped by a sheath. The trophic independence of algae for C and N makes them responsible for a natural fertility buildup of rice field soils. The nitrogen fixing ability of BGA was first recognized by Frank and Prantil in 1889. The occurrence of the BGA in the rice field was reported by FE Fritsch in 1907.

Azospirillum is a spiral-shaped nitrogen fixing bacterium. It also produces hormones and vitamins. Important species are Azospirillum brasilense and Azospirillum lipoferum. It is widely distributed in soils and grass roots.The genus Azospirillum belongs to family Spirillaceae with four commonly available species viz. A. brasilence, A. lipoferum, A. amazonense and A. halopraeferens or A. seropedicae (Fig. 8.1).

The first species of the genus Azotobacter, named Azotobacter chroococcum family Azotobacteriaceae, was isolated from the soil in Holland in 1901. Azotobacter represents the main group of heterotrophic free living nitrogen-fixing bacteria principally inhabiting neutral or alkaline soils. Azotobacter chroococcum and Azotobacter agilis were studied by Beijerinck (1901). In subsequent years several other types of Azotobacter group have been found in the soil and rhizosphere such as Azotobacter vinelandii, Lipman (1903); Azotobacter beijernckii, Lipman (1904); Azotobacter paspali, Döbereiner (1966), Azotobacter nigricans, Krasil’nikov (1949); Azotobacter armenicus, Thompson and Skerman (1981); Azotobacter salinestris, Page and Shivprasad (1991). A. paspali while A. agilis was categorized  under the genus Azomonas (Table 7.1).

Azolla is a free-floating water fern that floats in water and fixes atmospheric nitrogen in association with nitrogen fixing blue green alga Anabaena azollae. Azolla fronds consist of sporophyte with a floating rhizome and small overlapping bi-lobed leaves and roots. Rice growing areas in South East Asia and other third World countries have recently been evincing increased interest in the use of the symbiotic N2 fixing water fern Azolla either as an alternate nitrogen sources or as a supplement to commercial nitrogen fertilizers. Azolla is used as biofertilizer for wetland rice and it is known to contribute 40-60kg N/ha per rice crop. The agronomic potential of Azolla is quite significant particularly for rice crop and it is widely used as biofertilizer for increasing rice yields. Rice crop response studies with Azolla biofertilizer in the People’s Republic in China and in Vietnam have provided good evidence that Azolla incorporation into the soil as a green manure crop is one of the most effective ways of providing nitrogen source for rice.

The role of leguminous plants in improving the soil fertility is known for centuries. The nitrogen uptake in legumes by some unknown process was demonstrated through agronomic experiments by J.B Boussingault in 1838, which was opposed by Liebig and others. The presence of bacteria in the roots nodules of legumes was observed by P.G Lachmann (1858). M. Woronin (1866) further examined and observed them to be rod-shaped and motile.

Under agricultural conditions, the nitrogen removed is usually greater than the nitrogen input. To maintain fertility, nitrogen must be returned to the soil. This takes place mainly by biological nitrogen fixation, which is responsible for the major reduction of dinitrogen to ammonia that is used by the plants. Biological nitrogen fixation accounts for most of the fixation of atmospheric nitrogen in to Ammonium, thus representing the key entry point of molecular nitrogen into the biogeochemical cycle of nitrogen (Fig.4.1). Some bacteria can convert atmospheric nitrogen into ammonium. Most of this nitrogen fixing prokaryote is free living in the soil.

Biofertilizers can be defined as the preparations containing strains of micro-organisms which can augment the microbiological process viz. nitrogen fixation, phosphate solubilization or mineralization, excretion of plant growth promoting substances or cellulose or lignin biodegradation in soil, compost or other environments. Biofertilizers can be divided into nitrogen fixing bacteria, phosphate solubilizing and mobilizing microorganisms and organic matter decomposers as (Table 3.1 and Fig. 3.1):

On the basis of Nitrogen Fixation: On the basis of N₂ fixation, they are divided in to two sub categories as

2.1 Introduction

Microbes are the oldest form of the life on earth. These organisms date more than 3 billion years to a time when they were discovered with oceans. They are so tiny in size that million microbes can fit into the eye of a needle. Without microbes, we can’t live. Thus, understanding microbes is vital to understanding past and future. Microbes play many roles in the earth’s environment recycling dead plant and animal matter through the soil, removing CO2 from the atmosphere by photosynthesis in the oceans and nitrogen from the atmosphere to form nitrogenous fertilizers plants. Microbes play an important role in nutrient recycling, management, organic matter, decomposition and increasing the crop productivity and quality and protection against diseases (Panwar et al., 2009). Over the past century, many of the basic scientific principles of plant nutrition and soil fertility have been explained. In developed countries, inorganic chemical fertilizers have been widely accepted as a major source of improving and maintaining soil fertility.