eChapters

[Titrimetric/ Walkley and Black (1934) Method]

Introduction

The role of soil organic matter, in relation to soil fertility and physical conditions, are widely recognized. The organic matter is the source of plant nutrients which are released inassimilable forms during microbial degradation. A major proportion of N (95 – 99 % of the total), P (33 – 67 % of the total) and S (75 % of the total) in soils occur in organic combinations, which mineralize to release the nutrients in inorganic forms to be used by plants. Nevertheless, it serves as a reservoir of plant nutrients, in promoting water storage, and in regulating microbial activity.

The organic matter content of a soil varies from 0.344 % in very sandy arid soils to more than 86 % in Peats and Mucks. Soil organic matter contains 5 % N, and 0.5 % each of P and S, thereby, having a N:P:S ratio of 10:1:1. The organic matter content of a soil is estimated by the amount of organic carbon (C) present, as this element represents, on an average, 52 – 58 % of the organic matter, and the C:N ratio is 10 – 15. In the sub-soil, the average organic carbon amount is 36 – 44 % (40 %), and the C:N ratio is < 8. In order to find out the amount of humified organic material, the organic carbon content is multiplied by 1.724, which represents the ratio between the humus and the organic carbon (100/58) and is known as the ‘von Bemmlen factor ’.

The organic matter content of soils is estimated from the organic carbon, determined by using the ‘Titrimetric method / Walkley and Black method. The Titrimetric determination, also known as the ‘wet-digestion method’ involves a rapid titration procedure for the estimation of organic carbon content of soils.

The Electrical Conductivity (EC) of the soil is a measure of soluble salts present in the soil and is expressed as millimhos/cm or dSm^-1.

Principle

As the amount of the soluble salts in a solution increases, the electrical conductivity also increases. This electrical conductivity is measured in terms of resistance offered to the flow of current using a conductivity bridge.

It is known that solutions offer some resistance to the passage of current through them, depending upon the concentration of the soluble salts present. Hence, EC is measured in terms of electrical Resistance between parallel electrodes immersed in the soil water suspension.

In such a system, the solution between the electrodes becomes the electrical conductor to which the physical laws relating to resistance are applicable. The electrical resistance ‘R’ is directly proportional to the distance ‘L’ between the electrodes and inversely proportional to the cross sectional area ‘A’ of the conductor.

The pH is defined as negative logarithm of hydrogen ion concentration or the log of the reciprocal of the hydrogen ion concentration (Sorenson, 1906).

Principle

A glass electrode in contact with hydrogen ions of the solution acquires an electric potential which depends on the concentration of hydrogen ions. This is measured potentiometrically against some reference electrode which is usually a calomel electrode. The potential difference between glass electrode and calomel electrode is expressed in pH units.

Two electrodes are used in the determination of pH. One is reference electrode which provides a standard voltage and is usually a saturated calomel electrode which has two layers of saturated solution of KCl and mixture of solid HgCl₂ and Hg. The outer tube is usually 5-15 cm long, 0.5-1 cm in diameter. The mixture of solid HgCl₂ + Hg paste is contained in an inner tube that is connected to the saturated KCl solution in the outer tube by means of small opening. The resistance developed by this type of electrode is 2000-3000 Ohms.

The outer electrode is glass electrode that consists of a tube enclosing a lead wire made up of Ag coated with AgCl. This wire is again enclosed in a wax insulation. To the tube at the bottom is attached a glass bulb made up of a special kind of glass which is sensitive to hydrogen ions. The thickness of the glass membrane varies from 0.03 to 0.1 mm and has a resistance of 50 to 500 mega Ohms.

When these electrodes are dipped in solution, the saturated solution of KCl comes out of reference through small holes and forms an invisible ionic bridge between electrodes through which current passes. The hydrogen ions are absorbed by glass electrode and depending upon the amount of hydrogen ions present in the solution, an electric potential develops between electrodes. This potential difference is measured in terms of pH units by suitable Galvanometer.

(Keen-Rackzowski/Hilgard Apparatus Method)

Principle

With the capillary rise of water, the soil immediately above a water table gets saturated. The height upto which the soil is saturated depends on the texture, structure and packing of the soil mass. The experimental technique discussed herein permits approximation of maximum water holding capacity while determining the amount of water held in the soil at the point of saturation.

Principle

When water is ponded inside the concentric metallic rings driven into the soil, the rate of recession (fall) of the water level, or the rate of water withdrawn from a supply source used to maintain a constant head of water on the soil surface, gives the infiltration rate of the soil.

During infiltration of water into the soil, appreciable lateral movement of water may also occur. To avoid the error due to this lateral movement, two concentric rings are used. Equal heights of water are to be maintained in both the rings. The infiltration is measured in the inner ring only. The rate of water intake per unit area varies markedly with the size of the rings and the depth of the soil to which they are driven into. Infiltration rate studies are preceded by the profile, initial soil moisture and any other problems of the region in which the soil is located.

(International/Robinson’s Pipette Method)

Principle

This method is based on Stoke’s law. According to this law, the rate of fall of a particle in liquid is directly proportional to the square of its radius.

Bulk density is the mass per unit volume of soil including pore space. The normal range of bulk density in most soils is ranging from 1.02 to 1.80 g / cm³. The bulk density of coarse textured soils will be on the higher side while organic soils will have lower bulk density.

Particle density is the mass of soil per unit volume excluding pore space. Pore space is that fraction of soil volume not occupied by solid particles.

Principle

The bulk density and percent pore space are determined from the apparent and true volumes of the soil measures by adding a known quantity of water to a measuring cylinder contain a weighed quantity of soil.

Principle

Soil moisture content is determined by drying a known quantity of soil sample in an electric oven at 105° C to 110° C and finding out the loss in weight.

Soil is analyzed to know the nature of soil, to classify and advocate to farmers about the peculiarities of the soils and how much of fertilizers should be applied for better crop production.

A composite soil, of course, can not be moved to into a laboratory. The value of the laboratory work depends upon care in sampling. Each soil sample needs to be a fair representative of the specific area or horizon worth sampling.

If the sample is to be a representative of an area, it is necessary to take large number of samples spread over the area, pool them and sub-sample it so as to get a sample of desired size. For soil survey work, samples are collected from a profile which is typical of the soil of the surrounding area.

Principle

Equal volumes of all acids / bases containing their gram equivalent weights per litre of the solution react completely with each other.

More often, if the reagent is not a primary standard, a secondary standard solution must be prepared. The chemical is dissolved and made up or diluted to the desired concentration and then it is standardized against a primary standard or against another reliably known secondary standard solution. Such solutions are called as secondary standard solutions.

Principle

Standard solutions are the solutions of accurately known concentrations. There are two types of standard solutions viz., primary and secondary.

A known quantity of the substances is dissolved in a volumetric flask and the volume is made upto the mark. Standard solutions prepared in this way are known as primary standard. This method can be used for preparation of standard solutions of substances which satisfy the following conditions.

5.1 Volumetric Techniques or Titrimetric Analysis

Acid Base Neutralization Reactions-Acidimetry & Alkalimetry

Oxidation –Reduction Reactions-Oxidometry (Permanganometry) & Dichrometry

Practice to calculate the weight / volume of reagents required to prepare the following standard solutions.

Preparation of Standard Solution - (1 M, 0.1 M, 1 N, 0.1 N, 0.5 N, 5%, 10%, 20%, 10 ppm, 20 ppm, 100 ppm)

Instrumental methods of chemical analysis are the quantitative methods of analysis that use, as principal measuring devices, instruments other than those employed in conventional gravimetric and volumetric determinations.

The main basis for this method of analysis is the physical property of any particular element or compound being analyzed. These properties include:

2.1 Beakers

Beakers are the one of most important vessels used in laboratory which is made up of heat resistant glass.

They are available in various capacities ranging from 10 to 3000 mL.

For convenience of pouring solution, spout is provided in the beaker.

They are used to perform titrations & for boiling solutions, etc.,

Beakers are constructed in tall and low forms.

Analytical chemistry is a branch of chemistry dealing with the determination of constituents of a substance or mixture of substances.

1.1 Qualitative Analysis

Qualitative analysis deals with the identification of the constituents of a substance, mixture of substances, or solutions and the way in which component element or a group of elements are constituted.

1.2 Quantitative Analysis

Quantitative analysis is concerned with the determination of quantitative contents of individual element or group of elements or compound present in the substances. This branch of analytical chemistry is of enormous scope and importance in science, industry and agriculture. The quantitative analysis can be divided into several categories based on the different methods employed for their quantitative measurements such as:

5.1 Population Growth

In 2000, the world had 6.1 billion human inhabitants. This figure may rise to more than 9 billion in the next 50 years. For the last 50 years, world population multiplied more rapidly than ever before, and more rapidly than it will ever grow in the future. Anthropologists believe the human species dates back at least 3 million years. For most of our history, these distant ancestors lived a precarious existence as hunters and gatherers. This way of life kept their total numbers small, probably less than 10 million. However, as agriculture was introduced, communities evolved that could support more people.

World population expanded to about 300 million by A.D. 1 and continued to grow at a moderate rate. But after the start of the Industrial Revolution in the 18th century, living standards rose and widespread famines and epidemics diminished in some regions. Population growth accelerated. The population climbed to about 760 million in 1750 and reached 1 billion around 1800.

In 1800, the vast majority of the world’s population (86 percent) resided in Asia and Europe, with 65 percent in Asia alone. By 1900, Europe’s share of world population had risen to 25 percent, fueled by the population increase that accompanied the Industrial Revolution. Some of this growth spilled over to the Americas, increasing their share of the world total. The 2000 growth rate of 1.4 percent, when applied to the world’s 6.1 billion population, yields an annual increase of about 85 million people. Because of the large and increasing population size, the number of people added to the global population will remain high for several decades, even as growth rates continue to decline.

Between 2000 and 2030, nearly 100 percent of this annual growth will occur in the less developed countries in Africa, Asia, and Latin America, whose population growth rates are much higher than those in more developed countries.

4.1 Urban Issues

(i) Water Problem

The world’s population is increasingly found in the cities. Now a days, throughout the developing world, urbanization trends are gaining speed and are irreversible. From a technical standpoint, it is easier to provide water and sanitation services to people living closer together in urban settings than in dispersed rural communities. However, the costs of meeting the needs are much higher per capita, and are growing. The health risks posed by the lack of sanitation increase exponentially as densities increase and as people share drinking water and sanitation resources.

The urban environmental sanitation crisis in developing countries is taking a large health, economic, and environmental toll on all city residents. Willingness to pay for basic water and sanitation services is often high in peri- urban neighbourhoods, provided that services are appropriate, effective, and affordable. The use of a strategic sanitation approach should helps to build capacity within implementing agencies and enhances the ability of communities to make sustainable sanitation improvements.

(ii) Energy Problem

Energy is basic to development. Modern energy services are powerful engine of economic and social opportunity: no country has managed to develop much beyond a subsistence economy without ensuring at least minimum access to energy services for a broad section of its population. It is not surprising to find, therefore, that the billion who live in developing countries attach a high priority to energy services. On average, these people spend nearly 12% of their income on energy. At the same time, the provision of energy services especially through the combustion of fossil fuels and biomass can create adverse environmental effects. In rich countries, much attention is directed to the regional and global consequences of fuel combustion, because many of the local effects have been controlled at considerable expense over the past half- century. In developing countries, the local environmental problems associated with energy use remain matters of concern that are as, or even more, urgent than they were in industrialized countries 50 or 100 years ago. Further, it is the poor who suffer most severely from such problems, because it is they who are forced to rely upon the most inefficient and polluting sources of energy services for lack of access to better alternatives.

3.1 Air Pollution

Air pollution is a phenomenon by which particles either a solid or liquid and gases contaminate the environment. Such contamination can result in health effects on the population, which might be either chronic arising especially from long-term exposure or acute due to accidents. Other effects of pollution may be damage to materials, agricultural damage namely reduced crop yields and tree growth, impairment of visibility namely tiny particles scatter light very efficiently, and even climate change global warming.

3.1.1 Classification of Air Pollutants

Air Pollutants are classified as Natural as well as Anthropogenic. Natural pollutants are those that are found in nature or are emitted from natural sources. For example, volcanic activity produces sulfur dioxide, and particulate pollution may derive from forest fires or windblown dust. Anthropogenic pollutants are those that are produced by humans or controlled processes. For example, sulfur dioxide is produced by fossil fuel combustion and particulate matter comes from diesel engines.

Air pollutants are further classified as primary or secondary. Primary pollutants are those that are emitted directly into the atmosphere from an identifiable source. Examples include carbon monoxide and sulfur dioxide. Secondary pollutants are those that are produced in the atmosphere by chemical and physical processes from primary pollutants and natural constituents. For example, ozone is produced by hydrocarbons and oxides of nitrogen (both of which may be produced by car emissions) and sunlight.

2.1 Ecosystem

An ecosystem can be defined as a dynamic entity composed of a biological community and its associated abiotic environment. Often the dynamic interactions that occur within an ecosystem are numerous and complex. Ecosystems are also always undergoing changes or alterations to their biotic and abiotic components. Some of these alterations begin first with a change in the state of one component of the ecosystem which then cascades and sometimes amplifies into other components because of relationships.

The human activities of various kinds have resulted in caused a number of dramatic changes to a variety of ecosystems found on the Earth. Humans use and modify natural ecosystems through agriculture, forestry, recreation, urbanization, and industry. The most obvious impact of humans on ecosystems is the loss of biodiversity. The number of extinctions caused by human domination of ecosystems has been steadily increasing since the start of the Industrial revolution. The frequency of species extinctions is correlated to the size of human population on the Earth which is directly related to resource consumption, land-use change, and environmental degradation. Other human impacts to ecosystems include species invasions to new habitats, changes to the abundance and dominance of species in communities, modification of biogeochemical, and modification of hydrologic cycling, pollution, and climatic change.

1.1 Forest Resources

Forest resources usually provide the raw materials for homes, workplaces, the books and newspapers, and the packaging that contains food and other products of our labor. Forest ecosystems supply our water, maintain our climate, and help purify the air, protect soils, and provide for wilderness experiences. Forests provide habitat for wildlife, and serve as preserves of biological diversity. Forests are sources of food, fuel and medicine for people all over the world. Forests shape the recreational landscape, help stabilize our farms, and enhance our cities.

About 30 per cent of the world’s total land areas are covered by forest with the area of 3.9 billion hectares. Nearly 47 percent of the world’s forests are in the tropics, 33 percent in the boreal zone, 11 percent in the temperate zones, and 9 percent in sub-tropical areas. The 94 million hectares of forest lost over the ten-year period, represented about 2 per cent of the world’s total forest cover, or an area larger than Venezuela. Two thirds of the world’s forests are located in ten countries: the Russian Federation, Brazil, Canada, the United States, China, Australia, the Democratic Republic of the Congo, Indonesia, Angola and Peru. Most of the deforestation work was performed in natural tropical forests, which lost 14.2 million hectares a year over the last decade. Africa and South America have suffered the most deforestation.

Africa was the region with the highest deforestation in the world, which lost 5.3 million hectares of forest per year in the 1990s. Forests are a major factor in the climate change issue. Forest ecosystems contain more than half of all terrestrial carbon, and account for about 80 per cent of the exchange of carbon between terrestrial ecosystems and the atmosphere. Deforestation in the 1980s may have accounted for a quarter of all human-induced carbon emissions, the second greatest emitter after fossil fuels. Forest plantations comprise 5 percent of the world’s forests. Asia has the largest area of plantations, accounting for 62 per cent of the world total. China accounts for 24 percent of that total and India, 18 per cent. Plantations supply about 35 percent of the world’s round wood. The area of forest plantations increased by an average of 3 to 4 million hectares per year during the 1990s. Half of this increase was the result of afforestation on land previously under non-forest land use, whereas the other half resulted from conversion of natural forest. There are reports that 12 percent of the world’s forests, or about 480 million hectares, are in protected areas.

An agrometeorological observatory or station is a place where all the necessary instruments and structures are installed and maintained to observe and record the weather parameters at stipulated time interval.

Table 15.1. Instruments used for measuring weather parameters in observatories and laboratories

The climate system is the highly complex system consisting of five major components; the atmosphere, the hydrosphere, the cryosphere, the land surface and the biosphere, and the interactions among them. The climate system evolves in time under the influence of its own internal dynamics and because of external forcings such as volcanic eruptions, solar variations and human-induced forcings such as the changing composition of the atmosphere and land-use.

The term ‘climate variability’ is often used to denote deviations of climatic statistics over a given period of time (e.g., a month, season or year) from the long-term statistics relating to the corresponding calendar period. In this sense, climate variability is measured by those deviations, which are usually termed anomalies.

‘Climate change’ refers to a statistically significant variation in either the mean state of the climate or in its variability, persisting for an extended period (typically decades or longer). Climate change may be due to natural internal processes or external forcings, or due to persistent anthropogenic changes in the composition of the atmosphere or in land use. The United Nation’s Framework Convention on Climate Change (UNFCCC) defines ‘climate change’ as ‘a change of climate behaviour which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods’. The UNFCCC thus makes a distinction between ‘climate change’ attributable to human activities altering the atmospheric composition, and ‘climate variability’ attributable to natural causes. Climate change is a long-term shift in weather conditions measured by changes in temperature, precipitation, wind, snow cover, and other indicators.

A key difference between climate variability and change is in persistence of ‘anomalous’ conditions. In other words, events that are used to be rare occur more frequently, or vice versa. Occasionally, an event or sequence of events occurs that has never been recorded before, such as the exceptional tsunami in the Indian Ocean in 2004 or hurricane season in the Atlantic in 2005. Yet even that could be a part of natural climate variability. If such a season does not recur within the next 30 years, by looking back it could be called as an exceptional year, but not a ‘climate change’. Only a persistent series of unusual events taken in the context of regional climate parameters can suggest that a potential change in climate has occurred.

Weather forecasting is the application of science and technology to predict the state of the atmosphere for a given location. Forecasts based on temperature and precipitation is important to agriculture. Agricultural production is highly dependent on weather, climate and water availability, and is adversely affected by weather and climate related disasters. In many developing countries where rainfed agriculture is the norm, a good rainy season means good crop production, enhanced food security and a healthy economy. Farming in many parts of the world, especially in the arid and semiarid regions is risky, because climate is highly variable. A timely seasonal forecast of favourable conditions could permit farmers to adjust cropping patterns and input use in order to benefit fully from these conditions. Under rainfed conditions, even a less reliable, but earlier forecast may be more valuable than an accurate but late forecast.

In about 340 B.C., Aristotle described weather patterns in Meteorologica. Later, Theophrastus compiled a book on weather forecasting, called the Book of Signs. Ancient weather forecasting methods usually relied on observed patterns of events. This experience was accumulated over the generations to produce weather knowledge. However, not all of these predictions prove reliable, and many of them have since been found not to stand up to rigorous statistical testing. Two officers from of British Royal Navy, Francis Beaufort and Robert FitzRoy formed the basis for all of today’s weather forecasting knowledge by middle of 19th century. A terrible storm in 1859 inspired FitzRoy to develop charts to allow predictions to be made, which he called ‘forecasting the weather’, thus coining the term ‘weather forecast’. The ‘Weather Book’ which FitzRoy published in 1863 was far in advance of the scientific opinion of the time. By the early 20th century, scientists had begun to believe that weather forecasting could be predicted based on mathematical methods. Computers were first used to create surface analyses in 1992 and by 1998 digital imagery were used for satellite, radar and surface observations, encompassing nearly every factor of weather interpretation. Modern technology, particularly computers and weather satellites, and the availability of data provided by coordinated meteorological observing networks, has resulted in enormous improvements in the accuracy of weather forecasting.

The crops are very sensitive to climate. The crop production is dependent on climatic parameters like rainfall, light, temperature, relative humidity and carbon dioxide concentration. Each kind of cultivated crop plants has its own optimum growth requirements. Breeding and selection of new cultivars have allowed for a greater adaptability to less favourable growing conditions than was possible in the past, but the inherent climatic requirements of a specific kind of crop have not changed materially.

Weather and climate have also great influence on farm animal production. The environment in which an animal lives is referred to as its habitat. A habitat includes both biotic (living) and abiotic (non-living) components of the animals’ environment. Abiotic components of an animal’s environment include temperature, humidity, oxygen, wind, soil composition, day length and elevation. These potential environmental stressors can directly and adversely affect animal farming. The indirect consequences of weather include their impact on feed quality and availability.

There are various weather hazards that affect agricultural productions. These hazards affect crops and agricultural productivity negatively if they are not checked. Weather hazards include cyclones, droughts, floods, hailstorms, heatwaves and cold-waves. The hazard is distinguished from an extreme event and a disaster. An extreme event is simply an unusual event; it does not necessarily cause harm. A disaster is an event that does cause harm in significant amounts. Weather hazards are often called as natural hazards. The natural hazards become natural disasters when people’s lives and livelihoods are destroyed. Hydrologic hazards are the result of either excess or a severe lack of water, i.e., flood or drought. By issuing accurate forecasts and warnings in a form that is readily understood and by educating people about how to prepare against such hazards, before they become disasters, lives and property can be protected.

DROUGHT

Drought is a relative term used with reference to deficiency of rainfall when compared to normal rainfall of a given location. However, drought cannot be defined in terms of amount of rainfall or number of days without rain. Since ancient times droughts have had far-reaching effects on humankind by causing the failure of crops, decreasing natural vegetation, and depleting water supplies. Drought is different from other hazards; in that it develops slowly. It is a hazard that requires many months to emerge and that may persist for many months or years thereafter. This type of hazard is known as a ‘creeping’ hazard. Generally, this occurs when a region receives consistently below average precipitation.

In the Indian sub-continent, monsoon is one of the oldest weather observations, an economically important weather pattern over June through September every year. Due to its effects on agriculture, flora and fauna, and other economic, social, and environmental effects, a monsoon is one of the most anticipated, followed and studied weather phenomena of the Indian subcontinent. The word 'monsoon' is derived from the Arabic word mawsim meaning season.

The term 'monsoon' is traditionally defined as a seasonal reversing wind accompanied by corresponding changes in precipitation, but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with the asymmetric heating of land and sea. India Meteorological Department defines it as the seasonal reversals of the wind direction along the shores of the Indian Ocean, especially in the Arabian Sea, that blow from the south-west during one half of the year and from the north-east during the other half. The definitions include major wind systems that change direction seasonally. The cyclic change of wind and rain can be separated into the summer monsoon period characterised by warm and humid south-west winds, and the winter monsoon period characterised by dry and cool north-east winds. In fact, monsoon systems are a major feature of the general circulation of the atmosphere in subtropical latitudes of most regions of the world.

Clouds are the most important form of suspended water droplets caused by condensation. The World Meteorological Organisation defined cloud as a visible aggregate of minute particles of water or ice or both, in the free air. This aggregate may include larger particles of water or ice and particles such as those present in fumes, smoke or dust. The typical size of these water droplets and ice crystals range from less than 1 µm to 50 µm. When surrounded by billions of other droplets or crystals, they become visible as clouds. In the atmosphere sufficient moisture is required to allow condensation to take place. Then, moisture needs a suitable surface upon which it can condense. In free air, condensation begins on hygroscopic nuclei such as aerosols. These are microscopic particles and include dust, smoke, salts and chemical compounds. Nuclei range in size from 0.001 µm radius to over 10 µm. On an average, oceanic air contains one million condensation nuclei per litre and land air holds some 5 or 6 million. On hygroscopic particles such as sea salts, condensation can begin before the air is saturated. Supersaturation in clouds rarely exceeds one per cent. On average, clouds contain only four per cent of the total water in the atmosphere at any one time. Almost all clouds exist in the troposphere, although the tops of some severe thunderstorms occasionally extend to the stratosphere. Clouds move along with the wind and remain stationary in calm winds. They grow vertically and horizontally, depending on the temperature of the cloud and its ambient temperature. They may dissipate or precipitate. Under favourable atmospheric conditions, they burst and fall as rain. Clouds complete the following functions.

Precipitation is the deposition of atmospheric moisture on earth. All the water sources on the earth depend on precipitation only. Precipitation involves condensation, growth of hygroscopic nuclei, cooling of nuclei at different stages and their fall on to the earth's surface. If the cloud particles are too small and remain suspended in the sky, they may not fall on the earth. There may be several clouds but no precipitation. Under certain conditions, water particles formed tend to fall but do not reach the surface since they get evaporated on the way. Only when the cloud droplets or ice crystals grow to certain size and can no longer remain floating due to buoyancy of air, do they fall as precipitation.

FORMS OF PRECIPITATION

Precipitation form is the state that the moisture is in, i.e., liquid, freezing, or frozen (solid). Because atmospheric conditions vary greatly both geographically and seasonally, several different forms of precipitation are possible. All forms of precipitation are collectively termed hydrometeors. Hydrometeors have been classified into 50 specific types. Out of these precipitation forms, only rain (liquid form) and snow (solid form) make significant contribution to total precipitation. In many parts of the world, the term rainfall is used interchangeably with precipitation.

Water is the only substance that exists in the atmosphere in all the three phases, i.e., solid, liquid and gas. The moisture on the earth's surface is in a constant phase change. The moisture content of the atmosphere is about 0.035% of all fresh water. The atmosphere receives its supply of moisture from the earth's surface through evaporation from oceans, lakes, rivers, damp soil, etc. and through transpiration from vegetation. Water vapour is the gaseous state of water and is invisible. The amount of water vapour present in the atmosphere is called atmospheric moisture or humidity. It is a measure of the amount of water vapour dissolved in the air, not including any liquid water or ice falling through the air.

Water vapour is constantly being cycled between the atmosphere and the earth's surface. The input rate (the rate at which water vapour enters the atmosphere from the ground through evaporation) and output rate (the rate at which water moves from the atmosphere to ground through precipitation) are equal. The average length of time that individual molecules of water remain in the atmosphere is called the residence time. It can be found by dividing the mass of the substance in the atmosphere (in kilograms) by the rate (in kg per year) at which the substance enters to and exists in the atmosphere. The total volume of atmospheric water vapour at any instance over the globe is about 14000 km³, which is 0.001% of the hydrosphere.

Although water vapour is lighter than air, the combination of higher temperatures and the ocean source tends to restrict it to the lower atmosphere. The decrease of water vapour with elevation is quite important in many meteorological processes. Infact, most of the water vapour is contained within the lower 5 km of the atmosphere (> 90%) and more than half is actually contained within the lowest 1.5 to 2 km. Less than 5 - 6% of the water is above 5 km, and less than 1% is in the stratosphere.

Temperature is the physical property of an object that quantitatively expresses the hotness or coldness. Most of the weather parameters are dependent on temperature, directly or indirectly. It has important role to play in the development and growth of all living organisms in all stages of their growth. Atmosphere receives the heat energy from the sun and its temperature increases. Due to different amount of heat energy receipt at different places, the air temperatures at different places also vary. The variation in air temperature basically results into air motion, so as to equalize the energy content of the different regions of the earth. Thus, atmospheric temperature is one of the basic elements of weather and climate.

The temperature at a given location and time is affected by energy transfer processes including conduction, convection, advection and radiation. The controls of temperature include those factors that bring about spatial variations in temperature. The important factors that determine the temperature of a particular place on the earth’s surface are latitude, altitude, distribution of land and water, topography, ocean currents, prevailing wind, cloudiness, precipitation, nature of the surface, and turbulence.

The sun is a hot ball of glowing gases at the heart of the solar system. Its radiant energy is practically the only energy source to the earth. Very small and insignificant quantities of energy are available from other sources such as the interior of the earth, the moon, and other stars. Without the sun’s intense energy and heat, there would be no life on earth.

PROPERTIES OF SOLAR RADIATION

The mean distance of the sun from the earth, also known as one astronomical unit (1 AU), is approximately 1.496 × 10⁸ km, though the distance varies as the earth revolves round the sun in an elliptical orbit. At this average distance, light travels from the sun to earth in about 8 minutes and 19 seconds. The energy of the sunlight supports almost all life on earth by photosynthesis, and drives earth’s climate and weather. The minimum sun-earth distance is about 0.983 AU and the maximum is approximately 1.017 AU. The earth is at its closest point to the sun (perihelion) on around January 3 and at its farthest point (aphelion) on around July 4.

The sun makes up about 99.86% of the mass of the entire solar system. The visible disk or photosphere has a radius of 6.599 × 10⁵ km, and the solar mass is 1.989 × 10³⁰ kg. The sun is a completely gaseous body. The chemical composition (by mass) of the outer layers of sun is 71% hydrogen, 26.5% helium, and 2.5% heavier elements like oxygen, carbon, neon, and iron among others. Since the sun is not a solid body, different parts of the sun rotate at different rates. At the equator, the sun spins once about every 25 earth days, but at its poles the sun rotates once on its axis every 36 days.

Air in motion is called wind. Winds move moisture and heat around the world and also produce much of our weather. Winds are part of a global air circulation system that acts to balance temperature and pressure around the world. Any difference in temperature will always cause a difference in air pressure, and therefore, winds will blow. There are two types of movement in the atmosphere, horizontal movement and vertical movement. The term wind generally refers to the horizontal movement of air relative to the earth’s surface. Vertically moving air columns are called as currents. Upward and downward air currents are referred to as updrafts and downdrafts, respectively. Vertical motion in the atmosphere is of significance for the formation of clouds, precipitation and various types of storms. The horizontal differences in air pressure are far more variable than vertical changes and give rise to a wide range of air motions. Uneven distribution of pressure over the globe is balanced through the movement of winds. Winds also act as a means of transporting heat, moisture and other properties from one part of the earth to another.

Atmospheric pressure is the force per unit area exerted on a surface by the weight of air above that surface in the atmosphere of earth. The gas molecules of the atmosphere are pulled towards the earth by the force of gravity and hence exert a force on earth surface. Atmospheric pressure can be calculated as the summed weight of all gas molecules between a horizontal plane and top of the atmosphere and divided by the area of the plane. Low pressure areas have less atmospheric mass above their location, whereas high pressure areas have more atmospheric mass above their location.

Atmosphere can be defined as the gaseous envelope surrounding the earth. It is retained by earth’s gravity. The atmosphere has a mass of about 5.15 × 10¹⁸ kg, three quarters of which is within about 11 km of the surface. The imaginary ‘Karman line’ lies at an altitude of 100 km above the earth’s sea level, and commonly represents the boundary between the earth’s atmosphere and outer space. The study of earth’s atmosphere and its processes is called atmospheric science or ‘aerology’.

Meteorology is derived from the Greek word meteoro which means above the earth’s surface; i.e., the atmosphere. The state of the atmosphere experienced at a given time, in any location on the surface of the earth is known as weather. Thus, meteorology is the scientific study of the atmosphere or the weather. It is a branch of physics dealing with atmosphere and it is often quoted as the ‘physics of the lower atmosphere’. The main focus of meteorology is to understand the weather processes and forecast the weather. Solar radiation, the air mass and moisture are the three key ingredients that make up weather. The exchange of heat, moisture and momentum between the earth’s surface and the atmosphere determines the characteristic of weather. The observable weather events are known as meteorological phenomena and are defined by a set of variables called weather elements. Atmospheric temperature, atmospheric pressure, humidity, precipitation, cloudiness, wind and visibility, etc. are examples of such weather elements. The weather elements are not separate entities. They are closely related with each other and are highly variable in nature. Meteorology explains and analyses the changes of these weather elements.

The major subdivisions of meteorology are dynamic meteorology (or atmospheric dynamics) and physical meteorology (or atmospheric physics). The dynamic meteorology is concerned with the analysis and interpretation of the three-dimensional, time-varying, macro scale motions and energy transformations in the atmosphere. The science of dynamic meteorology is meant to develop models based on the hydrodynamic and thermodynamic equations. The physical meteorology is concerned with the processes that alter the physical properties and the chemical composition of air parcels as they move through the atmosphere.

Astro-meteorology is considered as one of the branches of Astronomy along with Astrophysics, Astrobiology and Astrometry. Astronomy is the science that deals with the material universe beyond the earth’s atmosphere. It studies the nature and constitution of Celestial (heavenly) bodies and the laws which govern them including the effect they produce upon one another. It seeks to unravel the probable past history of heavenly bodies and their development. There exists a confusion between the branches of Astronomy viz., Astrophysics and Astro-meteorology with the term Astrology. Astrophysics uses principles and laws of physics to explain how Celestial bodies form and function or in other words it will help to ascertain the nature of the astronomical objects, rather than their positions or motions in space. However, the Astrology and Astro-meteorology are the subjects deal in future prediction and often considered as pseudo-science which uses position and movement of stars and planets for that purpose. Astrology links these to predict the human behaviour, while that of Astro-meteorology links the same to predict the future weather.

From ancient days, these predictions are based on one’s wisdom and knowledge in astronomy and often these astrologers are astronomers who keenly watch the stars and planets movement and guide their rulers and farmers with their guesstimates. Till date it is being lore, mainly passed to followers of this group and the methodology is not documented clearly and properly. There are many incidences of falsified predictions of astrology as reported by many reviewers elsewhere and we are not discussing the same here, owing to our interest in weather prediction i.e., astro-meteorology only. However, we have to recognize the works of the ancient astrologers who helped in developing the astronomical science.

Basically, there are two approaches in astrology viz., geocentric and heliocentric as used by the practitioner of astrology worldwide. As the name implies the Geocentric astrology is based on the calculation of planetary position as seen by the observer from the earth and thus earth is centre, while Heliocentric astrology bases its interpretation upon position within solar system with reference to the sun as centre. Though in true sense, the sun is the centre, the effect of motion as manifest on the earth is the basis of most astrological interpretation. Hence, vast majority of astrologers employs the geocentric calculations of the planetary positions for their predictions.

Livestock population meet the protein requirement of humans in addition to meeting from plants. The food chain starts from fodder crops to animals and from animals to humans. In human physiology, digestion of plant protein is much easier than animal protein, but however the digestion depends on climate (temperate climate, sub-tropical climate, tropical climate etc.,) wherein human kind live. Similar to crops, there is strong interaction between livestock and meteorological weather elements (temperature, relative humidity, wind etc.). But detailed study has not been published elaborately in scientific journals in the past. The weather elements have greater influence on livestock productivity in terms of milk, meat, skin, wool etc., pest and disease infestation and their housing needs. In this chapter how weather elements influence shed management, pest and disease problem and animals’ productivity and are discussed. In majority of the Veterinary and Animal Science University in India, they have one division on animal climatology, wherein both research and extension aspects are being attended. However, in depth research is the need of the present decade, since little works have been done in the past on animal climatology.

Irrespective of weather elements, the heat stress due to the combination of temperature and relative humidity plays important role in affecting the productivity of animals. There is a range of thermal conditions within which animals are able to maintain a relatively stable body temperature by means of behavioral and physiological means. Heat stress results from the animal’s inability to dissipate sufficient heat to maintain homeothermy (Sejian et al., 2017). High ambient temperature, relative humidity and radiant energy compromise the ability of the animals to dissipate heat. As a result, there is an increase in body temperature, which in turn initiates compensatory and adaptive mechanisms to re-establish homeothermy and homeostasis. Homeostasis refers to the tendency to maintain a balanced or constant internal state that is optimal for functioning. Animals have a specific balanced or normal body temperature. When there is a problem with the internal functioning of animal body, this temperature may increase, signaling imbalance. As a result, body attempts to solve the problem and restore homeostasis for normal body temperature. These readjustments generally referred as adaptations and this is essential for survival of the animals.

8.1 Climate Change

Climate change is a broad term of global negative phenomena as created predominantly by burning of fossil fuels, which add heat-trapping gases to earth’s atmosphere. The over accumulation of greenhouse gases in the atmosphere lead to increased temperature and this is called as global warming. As a result, sea-level rise; ice mass loss in Greenland, Antarctica, Arctic and mountain glaciers worldwide; shifts in flowering/ plant blooming; and extreme weather events occur.

7.1 Importance of Weather Forecast in Agriculture

In India, agriculture is in reality to be a “gamble activity” with the monsoon rain, that means the productivity and profit from agriculture depend upon the goodness of the season. If any malevolent weather situation that happens during a crop season, whether it is at the beginning of the crop season or at the mid of the crop season or at the terminal of the crop season or at the whole of the crop season, the productivity of the crops raised would be under stake. In practice the irrigated crop area is lesser than the area under unirrigated crop in India in any region except the regions where irrigation is routed through perennial rivers. Normally the production from unirrigated crop is 30 to 40 per cent of the same crop grown under irrigated condition in an environment in the same season.

In India, in a region or in a taluk, if the irrigated area is lesser than 30 per cent of total cultivable area, there is every opportunity for the occurrence of food shortage. That means assured production depends upon irrigation rather than managing the crops with seasonal rainfall alone. This clearly indicates that the higher probability of occurrence of crop production risks falls under rainfed/dry land situation. The crop production risk is also common to irrigated area like unirrigated crop but the intensity gets varied. In this context one example that happened in India can be quoted. During December- January of 1982, with the occurrence of heavy rain/snow as a result of prevalence of western disturbance weather system, the wheat crop stood for harvest at Punjab got damaged with a loss of 124 crore of rupees. If this was anticipated earlier through weather forecast development, (which is common in all developed countries) and communicated to the farmers in advance, then the yield loss would have been reduced by following some tactical decisions to be taken either by the farmers or by the concerned Government. At that time, India did not have medium range weather forecast system and hence Indian farmers met with greater losses.

Under normal weather situation, agriculture depends on timely occurrence of rainfall for crop management activities irrespective of different farming situations namely, irrigated and unirrigated agriculture. Changes in temperature and rainfall pattern together with frequent occurrence of extreme weather events are major anticipated threats from the climate change that occurs now around the world. This threat in long run, if not addressed properly, would affect food security of a country. Pratap Narain et al., (2000) observed an increase in moderate and severe drought occurrence numbers in the arid zone of India during last decade (1991-2000) as compared to the earlier decades of the last century. Similarly, Pasupalak (2008) reported daily maximum rainfall of 400.3 mm in the last decade against earlier record of 256.4 mm (1969–78) in a location at Odisha State. Further the inter- annual variation within the decade did increase and also the number of rainy days with very heavy rainfall > 125 mm also found increased in the location against the daily mean rainfall of 20 mm/day in India.

A day may be with heavy rainfall or with bright sunshine or windy or in combination of these. When heavy rainfall continues for more than a week with some system like cyclone, floods may be the result. Similarly, if dry spell continues during a cropping season for more than 15 days, drought would initiate in that region. This is again depending upon the nature of the soil water holding capacity and nature of soils, topography and green cover of that region. In between these two extremes, we have normal season, where we get normal seasonal rainfall during a cropping season. Hence like dress code, in agro-climatology, there are three weather codes, namely floods code, drought code and normal code. The jargon weather code was developed by Dr.M. S Swaminathan in India. Across the countries of the World, if these weather codes occur, the impact would be universal. The strength of adaptation capacity to maneuver these extreme events by the farming community rests with their past experience made for similar situations, financial support and also the technology options that are available from the scientific institutions.

5.1 Introduction

A Crop Simulation Model is a mathematical model which describes crop growth and development processes as a function of environment, soil conditions, and crop management. Simulation model is a schematic representation which works on set of underlying assumptions, equations and algorithms, closely replicating the behaviour of the agricultural systems. A crop growth simulation model predicts the harvestable yield. Apart from this final state of crop production, the model also provides a host of quantitative information about major processes involved in the various stages of crop development. The information covers each component of the crop such as leaves, stems, roots and harvestable products as they change over time, including the changes in soil moisture and nutrient status.

An increase in the population, demands an increase in agricultural production with available resources. Efficient management of available resources under varying weather conditions is important for increasing agricultural productivity. Besides that, the emphasis of agricultural production changes from quantity to quality and sustainability (Aggarwal et al., 2000). Solution of these new challenges lies in understanding the interaction of the numerous elements affecting the plant growth and generating a crop growth model. This extremely complicated information needs to be processed and interpreted on a spatial scale. Information technology which has unleashed new frontiers in data analysis and automation is the driving force behind this model generation. These powerful computer programmes simulate the crop growth or yield of crops under various management regimes and provide near real time information to help farmers to make strategic decision in the management of their crops.

4.1. Introduction

Many countries have set up a network of agrometeorological observatories to regularly record important weather parameters such as clouds, rainfall, surface temperature, humidity, wind and wind direction, solar radiation, soil moisture, temperature and humidity profile of the atmosphere, etc. The observation process is performed either manually or through Automatic Weather Stations (AWS).

This recorded information is used for weather forecasting, natural resources management and for tracking agricultural production. However, these networks, which handle data of high spatial climate variability, are typically less robust than they should be. Moreover, the agrometeorological data collected from different ground stations is not transmitted in real time to a central collection point which limits the use of information.

Satellite remote sensing technology is an alternative system that is gaining popularity in the recent times which has allowed us to obtain frequent and precise measurements of vital agrometeorological parameters such as rainfall, solar radiation, temperature, evapotranspiration, albedo etc. Satellite data has many advantages over traditional ground stations, such as high spatial resolution (50 m–5 km), wide spectral bandwidth range (0.4–3.75 um) and high temporal frequency (even half an hour) and the prospect of collecting data from remote areas. In addition to routine repeated observations, satellites often provide synoptic views of the earth’s surface from space on a wide scale and have archive of information to create baseline data.

The preparation, planning and use of agricultural technologies for agriculture, needs application of agricultural meteorology. The role of agrometeorology in the last three decades has increased in terms of increasing food and nutritional security for the burgeoning population and natural resource management particularly in the context of global climate change. Agrometeorology can help to minimize inputs, thus clarifying the contribution of ecosystems and agriculture to the carbon budget in the event of global change. Agrometeorological information needs to be disseminated to users in time and space quite accurately, as agricultural activities are linked to the very local situation where the outputs of modern tools such as local area models, climate models, and dynamic crop simulation models are reduced to finer grid resolution and combined using GIS to extract practical suggestions. This chapter describes the recent applications of remote sensing in Agrometeorology.

The subject on micrometeorology deals with small scale meteorology of near ground surface with its related elements of both physical and biological processes. When this micrometeorology is integrated for crop production purposes, then it becomes crop micrometeorology, which is very important in the science of agricultural climatology. This crop micrometeorology gets varied with the architecture of the crops grown, available soil moisture, agronomical practices followed, soil texture, topography of the area, the nature of climate and weather that prevails etc. The soil surface heat, exerts a profound frictional effect on wind movements and hence it is different from the air layers at higher levels. These special features constitute the microclimate, which is modified compared to a flat bare surface by factors like topography, nature of soil surface, presence of vegetation and type of vegetative cover. The presence of crop canopy leads to distinct differences in the thermal and humidity regimes of the soil, the air layers immediately above it and the distribution of radiation and wind profiles inside the canopy. The study on the physical exchanges of the transfer of heat, momentum and moisture in the microclimatic region is called as micrometeorology (Venkataraman and Krishnan, 1992).

Radha Krishna Murthy (2002) reported that the micrometeorology is the micro scale of both the physical and meteorological factors that are taking place within the ecosphere. The ecosphere means the area between just above the crop canopy and just below the root zone of a crop. Further he was on the opinion that the microclimate of valley is important as compared to the entire climate of the mountain for the bio-life of valley. For the crops purpose, the microclimate is the climate of the ground surface to top of the crop canopy or otherwise it can be called as crop’s climate, a modified one from the Stevenson’s Screen climate/weather observation.

The climate, the past weather event that existed over larger region and covering long years of more than 30 years is very important for the emergence and successful sustenance of an organism including human kind. Normally scientists talk about environment and this includes not only the soils but also the climate of the particular region. Based on this, during 1989, the Planning Commission of India divided the entire India in to 15 agro-climatic zones based on physiography and climate. This division is only for planning purposes. Subsequently under NARP, the Indian Council of Agricultural Research (ICAR), New Delhi in consultation with the Planning Commission, requested all State Agricultural Universities (SAU) to divide their State in to different sub climatic zones considering soils, temperature and other weather parameters preciously with in the major agroclimatic zone of India in which the concerned State falls. Accordingly, each SAU has divided their State into different agro-climatic sub-zones and this resulted in 129 agro-climatic sub zones in India and limited to 127 and these all fall within 15 agro climatic zones of India as done by the Planning Commission of India.

The National Bureau of Soil Survey and Land Use Planning (NBSS&LUP), Nagpur not satisfied with this division, considering soils, temperature, rainfall, vegetation and all factors responsible for ecosystem (bio-climate, length of growing period, moisture index) divided the whole India in to 20 agro-eco regions by 1992 and revised preciously again by 2015 (Mandal et al., 2016) and the revised approach is being considered as scientific tool and taken for micro-level planning in India now and those are discussed at this chapter.

1.1 Weather Parameters

The atmosphere is a gaseous component surrounding the earth as an integral part and its interaction with ocean (water bodies), other planets of the solar system and land (Earth) generates one physical product namely weather elements (temperature, pressure, wind, humidity, precipitation, etc.,) and these form the weather and climate of the Earth. The process of generation of weather and climate of the region is purely natural and cannot be modified by the human being. But they can do adaptation to the existing climate and weather for their sustainable life. The weather can be defined as day to day change in the atmosphere in terms of heat and moisture exchange, while the climate is average of long period weather covering larger area or a region.

The particular climate of a region dictates/permits the genesis of a particular bio-organism in that domain and this selected organism’s growth and multiplication are triggered by the prevailing weather of that particular climate. Hence weather parameters of the atmosphere are very important to human being and other organisms of the Earth. The details on weather elements are given in question and answer section of this book (Annexure-I)

Soil fertility is the resultant of several factors, not the least important of which is the soil itself. Theoretically, the soil only plays the part of a support and could be very easily dispensed with and replaced by sand and even that can be replaced by a wire framework to support the plant mechanically and it will grow quite well if the right amount of nutrient materials have been added to water. ‘Where does the soil come in?” you will ask. The importance of the soil is two-fold: (1) It provides vast reserves of plant food which is slowly made available. (2) It provides limiting factors which restrict plant growth; these limiting factors must be neutralized. We have already discussed these reserve food materials and limiting factors in Chapter II.

It has been shown that if we treat a soil with dilute acid exhaustively we can remove everything from it except the mineral framework. If we try to grow anything in this mineral framework nothing will grow. Yet it is not like sand, for whereas in sand by adding appropriate amounts of nutrient materials in water solution you could grow a crop, nothing will grow if you added the same solution of nutrient materials to the soil. This mineral framework, therefore, is not inert like sand, but it is active and can react with the nutrient salts in such a way that either they are rendered unavailable or something else which is toxic is produced by the interaction between the soil and the nutrient salts. This mineral framework is not acted upon by dilute acids, but it reacts with alkalies in such a way that the alkalies are neutralized. In this respect, therefore, the mineral frame work behaves like an acid. With alkalies it forms salts and different alkalies are required in equivalent amounts for the formation of these salts. Thus we can have salts of a number of bases and if we use sodium hydroxide for neutralizing we shall have sodium soil, similarly we can have a calcium, magnesium or potassium soil. Now in nature, all the various bases principally, calcium, magnesium, sodium, and potassium, are associated with it in different proportions. The nature and amount of these bases determines the physico-chemical properties of the soil affecting crop yield and leading to soil infertility. We have already indicated the method of bringing the soiil to the normal state when it suffers from any of the defects associated with the soil framework.

Soil mechanics as a distinct branch of soil science is comparatively of recent growth. Its need arose from the fact that the requirements of the engineer are very often quite different from those of the agriculturist. Whereas the former would as a rule require hard, compact, impervious soil, the latter would have no use for it for the growth of his plants which require soft, friable and porous soil. The agriculturist generally has to look up to nature to help him out of his difficulties, the engineer has to depend on his scientific skill to modify the soil to suit his requirements. In this chapter an attempt will be made to explain in a simple language the requirements of the building, road, and irrigation engineer for particular types of soils and how they are met by modifying the soil if the required properties already do not exist.

Moisture plays by far the most important role in soils as regards vegetation. It is through the medium of water that the plants obtain their quota of mineral food vital for their growth. If water is gradually withheld from the soil, at a certain stage, the plant will begin to wilt and soon dry up. The soil may still contain some moisture but the plant is unable to make use of it. The minimum moisture in the soil below which wilting will take place is called the Wilting Coefficient and at one time great importance was attached to it. The determination of this Coefficient, however, is tedius. One must grow a number of plants and slowly watch them wilt and determine the moisture content at that point. Moisture content of the soil is determined by heating a weighed quantity of the sample in an oven kept at 100-110 ^oC. The moisture is expressed as percentage on the oven-dry soil.