eChapters

Introduction

Modern intensive livestock and poultry production has achieved phenomenal gains in the efficient and economical production of high quality and safe animal products and by-products. Furthermore, the overall performance of livestock can be increased by improving nutrients utilization, health status, fertility and efficiency of production. The use of feed additives has been an important part of achieving efficient livestock production. Feed additives are non-nutritive substances, preparations and micro-organisms that are added to animal feed to improve productive, reproductive and health performances. Any substance is considered as a feed additive when, not having a direct utilization as nutrient, is included at an optimum concentration in diet to exert a positive action over the animal health status or the dietary nutrient utilization. Hutjens (1991) defined feed additives as a group of substances that can cause a desired animal response in a non-nutrient role, such as pH shift, growth, or metabolic modifier. Feed additives are added deliberately to animal feed which may favourably influences characteristics of the animal feed, feed intake, gastro-intestinal flora, digestibility of the animal feeds, animal production, health, fertility and characteristics of animal products. Because of their chemical nature as active principles, additives are generally included in very small proportions in diet.

Introduction
India has vast animal genetic resources with a wide variety of indigenous farm animals including cattle. The cattle breeds have evolved over generations to adapt to the agro-climatic and socio-economic needs of the people. Domestic animal diversity is defined as the spectrum of genetic differences within each breed and across all breeds within each domestic animal species, together with the species differences; all of which are available for the sustainable intensification of food and agriculture production. The domestic animal diversity has evolved over millions of years through the processes of natural selection forming and stabilizing each of the species used in food and agriculture. Over the more recent millennia the interaction between environmental and human selection has led to the development of genetically distinct breeds. Selection processes, directed by both humans and the environment, together with the random sampling processes causing genetic populations to drift over generations, have accelerated the development of the diversity within species leading to the creation of distinct genetic differences amongst breeds.

Cattle Breeding Policies and Programmes in the Planning Process

It is necessary to see how the issues relating to Cattle Breeding have been dealt with in the successive Plan periods starting from the First Five Year Plan. It is seen that, while the issue of surplus cattle has been handled in different ways in the various Plan documents, some discussing this issue at great length and other remaining completely silent on the subject, other issues such as cattle development, genetic improvement and breeding etc., have also received varying degrees of emphasis in the different Plans. 

General Selection Procedures for Dairy Breeds
Selection of Dairy Cows
Selecting a calf in calf show, a cow in cattle show by judging is an art. A dairy farmer should build up his own herd by breeding his own herd. Following guidelines will beuseful for selection of a diary cow. Whenever an animal is purchased from cattle fair, it should be selected based upon its breed characters and milk producing.
History sheet or pedigree sheet which are generally maintained in organized farmsreveals the complete history of animal.The maximum yield by dairy cows are noticed during the first five lactations. So generally selection should be carried out during First or Second lactation and thattoo are month after calving.?Three successive complete milkings has to be done and an average of it will givea fair idea regarding production by a particular animal.
A cow should allow anybody to milk, and should be docile.?It is better to purchase the animals during the months of October and November.?Maximum yield is noticed till 90 days after calving.

Heterosis, hybrid vigor, or outbreeding enhancement, is the improved or increased function of any biological quality in a hybrid offspring. The adjective derived from heterosis is heterotic.Heterosis is the occurrence of a superior offspring from mixing the genetic contributions of its parents. These effects can be due to Mendelian or non-Mendelian inheritance.

The aim of mating systems are either to increase or decrease the homozygosity of the progeny compared with the parents or in some cases, to maintain the degree of homozygosity unchanged. This aim constitutes the basis of the following classification of mating systems:

Progeny testing in India was introduced in the late 1950’s the first sire index in our country was suggested by Krishnan (1956) which was, however, similar to the herdmate and contemporary comparison methods. Robertson and Rendel (1954) stated that an efficient method of sire evaluation should satisfy two conditions: 

Open nucleus breeding system is considered to be a best approach to bring genetic improvement in livestock. This system was first introduced New Zealand for faster genetic improvement of sheep. The milk recording under field condition is quite expensive.  Moreover, farmers are not under any obligation to retain the animal till the lactation is completed.  The generation interval is also very large as it takes about 6-7 year by the time complete record on progeny testing programmes in developing countries is available, so that the effective genetic improvement is small.  Use of best proven bull on the elite cow, which are best 5-10% of the cow for genetic improvement of the population. The net genetic gain in the herd considering the actual genetic improvement from various parents off spring path is around 0.7% per annum.  Considering these situation in develop countries it has been proposed that ‘nucleus’ herd be created where males from the best cows are obtained.  The nucleus herd would be open in the sense that the lowest yielding cows are culled every year and are replaced by procurement of that many high yielding cow from farmers herd.  The nucleus herds are utilized entirely for production of males for breeding purposes in the population.

An animal breeder usually interested in various economic traits and when wishes to improve them in the herd/flock, he has three general methods at his disposal. Tandom method, independent culling level method and  index selection method.

Tandom Method

It involves selection for one trait at a time and until it reaches at a satisfactory level, and then for a third trait etc. This method is applicable only when the different traits in question are entirely independent or positively genetically associated to each other. Its effectiveness decreases with the increase in number of traits. This method is least desirable of all the methods.

Individuality tells us what an animal seems to be; his pedigree tells us what he ought to be, but the performance of his progeny tells us what he is
Effectiveness of selection depends on ability to recognize those animals, which possess superior inheritance. Those superior animals must be mated together for the production of offspring. The aids available to estimate the breeding value of an animal is through the phenotype of an animal or its relatives.

The response to selection is the change produced in the population mean through selection. This is achieved through selecting as parents of the next generation, individuals with highest genetic merit and whose progeny will, as a group, have the highest possible genetic merit for the trait in question. 

Selection is an important tool for changing gene frequencies to better fit individuals for a particular purpose. It may be defined as a process in which certain individuals in a population are preferred to others for the production of the next generation. Selection is of two kinds

In genetic studies it is necessary to distinguish two causes of correlation; is chiefly pleiotropy, though linkage is a cause of transient correlation, particularly in populations derived from crosses between divergent strains. Pleiotropy is simply the property of a gene whereby it affects two or more characters, so that if the gene is segregating it causes simultaneous variation in the characters as affects. For example, genes that increase growth rate increase both stature and weight, so that they tend to cause correlation between these two characters. The degree of correlation arising from pleiotropy expresses the extent to which two characters are influenced by the same genes. But the correlation resulting from pleiotropy is the overall, or net, effect of all the segregating genes that affect both characters. Some genes may increase both characters, while others increase one and reduce the other the former tend to cause a positive correlation the latter a negative one. So pleiotropy does not necessarily cause a detectable correlation. The correlation resulting from environmental causes is the overall effect of all the environmental factors that vary; some may tend to cause a positive correlation, others a negative one.

Estimates of heritability use statistical analyses to help to identify the causes of differences between individuals. Because heritability is concerned with variance, it is necessarily an account of the differences between individuals in a population. Heritability can be univariate–examining a single trait – or multivariate – examining the genetic and environmental associations between multiple traits at once. This allows a test of the genetic overlap between different phenotypes: for instance hair colour and eye colour. Environment and genetics may also interact, and heritability analyses can test for and examine these interactions (GxE models).

The concept of value, expressible in the metric units by which the character is  measured. The value observed when the character is measured on an individual is the phenotypic value of that individual. All observations of means, variance, or covariances, must clearly be based on measurements of phenotypic values. In order to analyse the genetic properties of the population we have to divide the phenotypic value into two componants. 
The first division of phenotypic value is into components attributable to the influence of genotypic and environment. The genotype is the particular assemblage of genes possessed by the individual, and the environment is all the non-genetic circumstances under the term ‘environment’ means that the genotype and the environment are by definition the only determinants of phenotypic value. The two components of value associated with genotypic value and the environmental deviation. 

The amount of variation is measured and expressed as the variance. When values are expressed as deviations from the population mean the variance is simple the mean of the squared values. For example, the genotypic variance is the variance of genotypic values and the environmental variance is the variance of environmental deviations. The total variance is the phenotypic variance of the variance of phenotypic values, and is the sum of the separate components. 

Gene Frequency

A population, in the genetic sense, is not just a group of individuals, but a breeding group and the genetics of a population is concerned not only with the genetic constitution of the individuals but also with the transmission of the genes from one generation to the next. In the transmission the genotypes of the parents are broken-down and a newest of genotypes is constituted in the progeny, from the genes transmitted in the gametes. The genes carried by the population thus have continuity from generation to generation, but the genotypes in which they appear do not. The genetic constitution of a population, referring to the genes it carries, is described by the array of gene frequencies, that is, by specification of the alleles present at every locus and the numbers of proportions of the different alleles at each locus. If for example, A1 is an allele at the A locus, then the frequency of A1, is the proportion or percentage of all genes at this locus that are the A1 allele. The frequencies of all the allele at any one locus must add up to unity, or 100 percent. 

Quantitative Versus Qualitative Inheritance

There is a continuum of traits being inherited as a Mendelian trait with simple inheritance and traits having quantitative inheritance without well separated classes and with many genes involved.
Classification of traits in relation to mode of inheritance and environmental tolerance are shown in Figure 1.2. First there are the well known traits with simple Mendelian mode of inheritance. The trait with quantitative genetic inheritance is caused by segregation of many gene pairs, each with small effect. At the same time the trait is influenced by a lot of minor environmental effects.
Diseases will often be ‘either/or traits’ as the simple Mendelian traits. Cases in which the severity of the disease has a normal distribution can also be found. In many production diseases the disease only occurs when a genetically prone individual is exposed to adverse environmental effects. Figure 1. Classification  of traits in relation to mode of inheritance  and environmental tolerance. 
 

Introduction
Statistics is a field of mathematics that pertains to data analysis. Statistical methods and equations can be applied to a data set in order to analyze and interpret results, explain variations in the data, or predict future data. A few examples of statistical information we can calculate are:
Average value (mean)

There are certain inherited traits (characters) in various species of livestock which are economically important. These traits have to be improved for increased production like milk, meat, egg, wool, etc.

Definition of Breed

A breed is a group of animal’s related similar characters like general appearance, size, features and configuration etc. A group of individual which have certain common characteristicsthat distinguish them from other groups of individuals is known as Species.

Domestication of Livestock

Domestication (from Latin domesticus) is the process whereby a  population  of  animals  or plants is changed at the genetic level through a process of selection, in order to accentuate traits that benefit humans. It differs from taming in that a change in the phenotypical expression and genotype of the animal occurs, whereas taming is simply the process by which animals become accustomed to human presence. In the Convention on Biological Diversity, a domesticated species is defined as a “species in which the evolutionary process has been influenced by humans to meet their needs.” Therefore, a defining characteristic of domestication is artificial selection by humans. Humans have brought these populations under their control and care for a wide range of reasons: to produce food or valuable commodities (such as wool, cotton, or silk), for types of work (such as transportation, protection, and warfare), scientific research, or simply to enjoy as companions or ornaments. Plants domesticated primarily for aesthetic enjoyment in and around the home are usually called house plants or ornamentals, while those domesticated for large-scale food production are generally called crops. A distinction can be made between those domesticated plants that have been deliberately altered or selected for special desirable characteristics and those plants that are used for human benefit, but are essentially no different from the wild populations of the species. Animals domesticated for home companionship are usually called pets while those domesticated for food or work are called livestock or farm animals.

Introduction

From the very early days human beings depend on animals and animal products for food and other requirements. In dairy and poultry farms high yielding animals are reared. These high yielding animals are produced by hybridization experiments. Previously the animals were developed basing on unscientific methods. Before the discovery of principles of heredity human beings have selected the animals with required characters and learned to develop the plants having the selected characters. This phenomenon is called Artificial selection. However, an increased knowledge of biology, especially genetics, has helped in improving the quality of animals and animal products as per the human requirements.

6.1 PROCESSES IN THE DOMESTICATION TECHNOLOGY

6.1.1 Introduction

The world Agroforestry centre Former international Centre for Research in Agro – forestry (ICRAF) and other home base orgainsation in their programme Africa Humid Tropics Regional programmed are the leader in the science and practice of integrating working trees on small farms and in rural landscapes. In this programme trees that ensure security in food nutrition income, health, shelter and energy and a regenerated environment are domesticated. The mission of this is to increase; diversify and stabilize income, food and health strategies from practicing agroforestry approaches in general domesticating indigenous trees and their products particular.

Definition of Agroforestry

Basically agro forestry is the integration of agriculture forestry and sometimes animal production. This is a measure to maintain soil fertility, stop desertification and soil degradation. Foresters and agriculturalist have long recognized the important of these approached which have been incorporated into forestry law of severe countries. This does not only involve the planting of certain trees in farms but also the protection of certain trees species which are not to be felled or damaged during farming.

5.1 PRODUCTION METHODS OR DIFFERENT TYPES OF PLANTS PRODUCED IN THE NURSERY

The different types of plants produced in the nursery include plants in plastic bags, bare-root plants, stumps, pseudo estacas, root trainers, copper coated trainers and jiffy pellets.

The most common production techniques may not always be the best. Bare-root plants and pseudo estacas are easy to transport to the field, but their survival and growth are usually very poor. Plastic bags are cheap and easily available, but they result in coiled roots and are heavy to carry to the field. Root trainers, copper coated trainers and jiffy pellets are alternative systems which may have higher initial costs for the nursery. However, the farmer will receive the benefit of fast growth and high survival in the field

4.1 THE NURSERY
We distinguish several types of nurseries among which we have Permanent nursery and Temporal or Seasonal nursery.
4.1.1 Permanent nursery
Permanent nursery is a large nursery destined to produce large number of plants for several years or in other words, the place is used for several years even if the plantation center is far. It is also called the central or industrial nursery. For example, the Cameroon Development Corporation [CDC] with head quarter in Limbe has its central nursery in Bota – Limbe. Here oil palm seedlings are being transported from the nursery in Limbe to the Bomboko area in Idenau Subdivision and Illoani in Ndian Division. A special management practices is being carried out in this type of nursery notably:
• Access road for vehicles accessible in all seasons ;
• Forecast annual rotation of surface area and annual production of plants;
• Forecast species with permanent shelter to serve for the protection of pots;
• Anticipated area for irrigation systems;
• Construct a shade, store, office and a guard’s room;
• Forecast methods of plant preservation for plants destined to be transported to far stations.

3.0 INTRODUCTION

There are two main types of plant reproduction / multiplication that are used and these include sexual reproduction known as seed propagation / multiplication and the asexual reproduction known as vegetative propagation / multiplication. Propagation is most often by seeds produced by plants or by plant parts like vines, roots, tubers, suckers, etc. Propagation is the natural mechanism by which plants regenerate. Seed is the organ of reproduction in flowering plants.

3.1 SEXUAL REPRODUCTION OR SEED PROPAGATION TECHNIQUES

Seed is the organ of reproduction in flowering plants. Sexual reproduction is propagation by seeds. This is the main method by which plants reproduced in nature as most plants produce seeds except in species that have separate male and female plants; e.g. Njansang (Ricinodendron heudelotii) and Black fruit (Canarium schweinfurthii)

Seed multiplication seems to be the most practicable technique by the farmers. Example Agroforestry Species that are mostly propagated by seeds are Sweet Bush mango [Irvingia garbonensis], Bitter Bush mango [Irvingia wombolo], Bitter kola, Kola nitida, Kola acuminata, Njansang [Ricinodendron heudelotii].

2.1. GERMPLASM COLLECTION
a. Propagation techniques
There are four main propagation techniques that are used in plant reproduction for most plants, viz;
• Seed
• Cuttings
• Marcotting
• Grafting
Note: That not all plants can be propagated by all the four methods mention above.

1.1 DEFINITIONS
1. Forest
Forest is the homeland of trees. Because man must protect and maintain the life of the forest and because of this;  certain natural
calamities  and  bad  use  of  the  forest  constitute  severe danger to  the forest  and the  environment at large.  In  other to divert from these difficulties, man was bound to cultivate trees. This is silviculture. Silviculture then became a science and art.

The communication system provides the forecaster with a large mass of figures; the next step is to put them into a suitable form for study. This is done by plotting the observations on a large outline map which in popular term is called a “Weather map” technically a “Synoptic chart” simplified synoptic charts appear in some newspaper.

A chart or map on which meteorological data presented and analysed is called a synoptic chart. Synoptic means having the same view point. The representation of the meteorological data in synoptic chart are atmospheric wind, temperature, pressure, cloud, precipitation, dew point etc., over a long area at a given local standard times.

Naturally Greenhouse gases are cover as blanket on the Earth and kept it about 33⁰C warmer than it would be without these gases in the atmosphere. This is called as the “Greenhouse Effect”.

Over the past century, the Earth has increased in temperature by about 0.5⁰C and many scientists believe that this is because of an increase in concentration of the main greenhouse gases viz., carbon dioxide, methane, nitrous oxide and fluorocarbons. People are now calling this climate change over the past century the beginning of “Global Warming”.

The earth has two motions. (1) Rotation and (2) Revolution. The earth rotates about its axis (west to eastward) with a speed of 464 m/s or 1669 km/hr. Its angular speed of rotation is about 7.29 x 10^-5 radians/sec or 0.26244 radians per hour. This rotation causes day and night and diurnal variations of weather.

The rotating earth revolves round the sun in an elliptical orbit (with the sun at one of its Foci) with a speed (orbital speed) of about 1.073 x 10⁵ km/hr or 29770 m/s or 29.8 km/s. This revolution causes seasons. It has been stated earlier that the apparent path of the sun with respect to the celestial sphere is called ecliptic.

Crop yield is influenced by genetical (heredity), external (environmental) and management factors that occur during the crop growing period. The external environment is the climate which regulates and determines the growth and development and final output of crop plants. But, man has no control over weather, hence it is dominance over the success or failure of agricultural enterprises. According to the World Meteorological Organization, the weather induced variability in crop yield is as high as 50 per cent. Therefore, weather should be taken as one of the inputs in agricultural planning.

Variation in field crops between years is associated with many factors. This is mainly due to weather, soil and management factors. There is complex reaction of weather variables among themselves as well as with other factors. Therefore, many attempts were made to study the effect of weather variable on crop yield through simulation modeling.

Environment in which crops are grown dictates their final yield. Of these environmental factors, climate and weather the uncontrolable factors, have maximum influence on crop productivity. Vagaries of weather subject a crop to different ecological situations from year to year leading to differential responses of crops to input resources. This situation limits the use of costly inputs for realizing optimum yield. While weather itself cannot modify, the hazardous weather can often be mitigated by agronomic management. Therefore, the primary requirement for initiating agronomic measures against weather hazards is foreknowledge of weather situation that is likely to develop in an area.

Climate, in general, is the totality of weather during a longer period and over wider area. Agro climate can be defined as the conditions and effects of varying weather parameters like solar radiation, rainfall etc., on crop growth and production.

Climatic classification is a method of arranging various data of climatic parameters to demarcate a country or region into homogenous zones i.e., places having similar conditions.

Season is a period in a year, comprising few months during which the prevailing climate does not vary much. Growing season for a crop is more important for its yield and other management practices, to be followed.

Indian Meteorological Department has divided the year into four seasons.

Plant growth is resultant of all the environmental factors – climatic, physiographic, edaphic and biotic factors.

For a particular field – it is primarily a function of climate with temperature and light – being the most important factors. – Close relationship exists between plant phenology and both latitude and altitude.

The Sun is the primary source of heat to the Earth and its atmosphere. The heat received from other celestial bodies as well as the interior of the Earth is rather too significant. The distance that separates the Earth from the Sun is about 149.0 million km. The diameter of the Sun measures roughly about 1.3824 million km. The surface temperature of the Sun is estimated between 5500^o C and 6100^o C. (or 5762^o K).

The weight of the sun is about 1.9 X 10 30kg. The radius is 6.97 X 10 8 m or the diameter of the sun is 14 X 10 5 km. The mass of the earth is 6 X 10 24 kg, the radius is 6.4 X 10 6 m. The gravitational force of the earth is 9.81m/s². Whereas the sun‘s attractive force is 274m/s². This is 25 times higher than earth’s gravitational force.

El Nino means ‘The Little One’ or ‘Christ Child’ in Spanish. It was originally recognized by fisherman of the coast of South America as the appearance of usually warm water in the Pacific Ocean, occurring near the beginning of the year i.e. around Christmas. That is why the name is used. El Nino, the periodic warming of Pacific Ocean waters that affects the weather worldwide. C. Fred and T. Andrus of the University of Georgia studied the ancient fish bones from refuse left about 6000 years ago by ancient peoples in Peru and found that ocean catfish lived in water that averaged 60 to 70 warmer than now and that there was little variation in temperature. He concluded that if El Nino was occurring at the modern rate, once every two to seven years, then the bones from the fish would have reflected the temperature variation.

The march of weather factors during crop period is never smooth and regular. Agriculture, because of its dependance on climate is inevitably subjected to unpredictable long and short term fluctuation characteristic of atmosphere conditions. Climate introduces an element of risk in farming which makes it particularly hazardous occupation.

A Weather hazard in this context can be defined as any type of extreme weather condition that can damage the crops and animals leading to abnormal decrease in production and income. The extent to which these hazards create risk depends on the time of occurrence, intensity and duration of the hazard besides the age, stage of development and inherent resistance of the crop or livestock involved. Major abnormalities affecting the crop production are:

Cloud usually consists of very small droplets of water which cannot fall appreciably below the cloud base without evaporation. In this condition clouds are stable. Rain drops are about a million times heavier than cloud drops and rain develops only if the cloud droplets grow by some mechanism. Cloud Seeding mechanism depends on the difference in vapour pressure over ice and super cooled cloud, water evaporates of the droplets and migrate to the ice crystal, which grows and begins to fall increasing their growth rate by coalescence with other droplets and eventually melting and falling as rain drops. Presence of ice nuclei determines whether ice crystals form in a supercoold cloud or not. Ice crystals form on naturally occurring nuclei at temperatures of – 10⁰ to 30⁰ C. At warmer temperatures, either the efficient ice-forming nuclei are often deficient in the atmosphere or the cloud may occur with tops supercooled but not to an extent which activates the ice nuclei available. It should be possible to initiate precipitation by introducing ice crystals or by supplying artificial nuclei.

The change of state of water from solid and liquid to the vapour and its diffusion into the atmosphere is referred as Evaporation. In the meteorology, evaporation is defined as the maximum possible loss of moisture from a wet, horizontal, flat surface exposed to weather which exist in the vicinity of plants.

FACTORS AFFECTING EVAPORATION

1. Those affecting water supply at the evaporating surface. i.e., soil and plants including soil storage capacity, rainfall and irrigation and

2. Those affecting energy supply to the evaporating surface like solar radiation.

Hydrological cycle involves four major steps, Viz., Evaporation, Transpiration, Condensation and Precipitation. Though the cycle has neither a beginning nor an end, the concept of cycle begins with the water of oceans, since it occur nearly ¾ of the Earth’s surface. Radiation from the Sun, evaporates water as water vapour from the oceans into the atmosphere. The water vapour rises and collects to form clouds. Under certain condition, the cloud moisture condenses and falls back to the Earth as rain, snow, hail etc. Precipitation reaching the Earth surface may be intercepted by vegetation or enter into the soil, may flow as run-off or may evaporate.

Evaporation may be from the surface of the ground or from free water surface. Transpiration may be from plants.

Condensation: The physical process by which a vapour becomes a liquid or solid – opposite of evaporation.

Cloud has been defined as a visible aggregation of minute water droplets and / or ice particles in the air, usually above the ground level.

CLASSIFICATION OF CLOUDS

Though confusion apparently arises from the number of kinds or species, the genera seems reasonably clear out, if we are able to recognize their main characteristics.

Clouds are usually classified according to their height and appearance. For convenience, we list them in descending order. High clouds, middle clouds and low clouds are some forms do not fit in any of these categories. But fortunately their particular characteristics make them easily identifiable as vertical development clouds. We must exercise some caution in studying on height. There is some seasonal as well as latitudinal variation and there is some overlapping from time to time. However, the appearance of clouds is quite distinctive for each height category.

Air Constantly moves from place to place due to pressure differences which are caused by difference in temperature.

Wind has been defined as air in horizontal motion. According to Byers, “The wind is simply air in motion, usually measured only in its horizontal component”. According to Trewaitha, “Wind is simply air moving in a direction which is essentially parallel with the Earth’s surface.

There are two types of movement of wind in the atmosphere.

1. Horizontal movement

2. Vertical movement (Currents)

The primary wind circulation in Northern and Southern hemispheres is seen in figure on page 51.

Moisture present in the atmosphere plays a significant role in weather and climate of the region. There are three major components in the atmospheric moisture.

  I. Humidity

 II. Precipitation

III. Evaporation.

Humidity: The terminology related to humidity and concerned with gaseous form of water i.e. water vapour, several expressions of the amount of water vapour in the air is used. They are as follows.

The atmospheric pressure is weight of the air which lies vertically above an unit area centered at a point. Normal pressure of air is 1.034/cm².

Pressure is defined as the force per unit area.
At the surface of the earth the atmosphere air exerts a pressure of about 10⁵ Newtons/m² or 10⁵ Pascals, which is called one bar or one atmosphere. Evangelista Torricelli (1608-1647) devised a method for measuring the atmospheric pressure by mercury (Hg) barameter in 1643.

In climatology, terms “Weather” and “Climate” have different connotations. Weather refers to the state of atmosphere at any given time denoting the short- term variations of atmosphere in terms of temperature, pressure, wind, moisture, cloudiness, precipitation and visibility. Weather is highly variable. It is constantly changing, sometimes from hour to hour and at other times from day to day. The aforementioned properties of the atmosphere are subject to constant change and their state at any time determines the state of the weather. However, weather elements are not separate rather they are closely related with each other.

David I. Blumenstock, an eminent climatologist has defined the weather in more restrictive sense. According to him, weather is the behaviour of the lower atmosphere with particular emphasis on the atmospheric behaviour which affect the lands and oceans and have a marked influence on the organisms that live upon the lands, within the waters of the earth or in the lower air. For the geographer, this definition of weather is more satisfactory. Since, he is interested more in the working of the lower atmosphere which affects the life of man as well as natural environment directly. Thus, we come across a great many varieties of weather covering a wide range of conditions.

Geological evidence suggests that the age of the earth is about 4,50,00,00,000 (4.5 billion) years and life began on earth between 0.6 to 1.0 billion years after earth has formed. That is life began on earth some where 4 to 3.5 billion years ago.
The plant kingdom over the globe produce oxygen about 30,00,00,000 (3 million) kg per second which is consumed by the living beings on the earth. Air which is present in the atmosphere is a mechanical mixture of gases. The various gases, solid and liquid particles in the air that envelope the earth are bound to it by the gravitational attraction. This complex content of gases, solid and liquid particles is called atmosphere. The atmosphere extends above the surface of the earth to great heights. There is no sharp boundary between the atmosphere and the outer space. For our convenience, the height of the atmosphere is taken as 1000 km. The lowest one km which is called planetary boundary layer, contains 10 per cent of the mass of the atmosphere. All biological and human activities are confined to this planetary boundary level. The mass of the atmosphere is about 5.6 x 1018 kg (mass of earth is 6 x 1024 kg). The mass of the oceans water is about 1.4 x 1021 kg. This shows that the mass of the oceans is more than 250 times the mass of the atmosphere. The density of the dry air at the earth surface is 1.225 kg/m3 and at an altitude of 5.5 km this drops to 0.66 kg/m3 and at 30 km altitude it is about 0.013 kg/m3.