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The chemistry of humic substances is the least comprehended in the field of Soil Science. The many important functions of humus will remain obscure if the structural chemistry of the humic and fulvic acids is not known. A variety of functional groups have been reported in humic substances. However, considerable disagreement still exists in respect of the exact amounts present and, in some cases, proof of existence is lacking.

Some important structural groups of organic molecules are given below:

1.1 Man’s place in Nature

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

Proportion of solid, liquid (water), and gas (air) components in a soil mass indicates physical conditions such as soil structure, porosity and water content. A well Structured soil may have a high pore volume whereas a compacted soil may have little pore-space for other phases to occupy. In general, soil solids may occupy 50 % of the soil volume in a well-aggregated fertile loam and the remaining volume may be occupied by liquid and gases interchangeably.

Organic matter is of immense importance in forming good aggregates in a wide range of soil types, particularly those representing Mollisols, Alfisols, Ultisols and Inceptisols. Organic matter is somewhat less important in the Oxisols where hydrous oxides may play apredominant role. These relationships are depicted in Fig. 13.

Fig. 13.1: Relationship between OM and the formation of soil aggregates

Aggregates do not directly influence plant growth, but they alter the physical and chemical environments in which plant roots grow through their effects on porosity, aeration, moisture retention, etc., when well-irrigated, even fine- textured soils permit adequate exchange of gases with the atmosphere. The polysaccharides of soil have received the greatest attention in producing stable aggregates, but other organic substances bonded to clay through association with Fe or Al may also be involved.

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.

Humic substances, the natural organic materials, represent a mixture of relatively small organic components, which form supramolecular structures held together by dispersive forces such as n - n and van der Waals’ interactions. Identification of the best analytical method for complete characterization of humic substances is still being discussed. Humic substances differ in molecular weight, elemental composition, acidity and cation exchange capacity and often are classified into three major fractions according to their solubility as humic acids, fulvic acids and humins.

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.

Review of the state of art of Drought on impact assessment, monitoring and management with special reference to agricultural production has revealed that Drought is still a complex natural disaster and difficult to forewarn in spite of advancements in atmospheric sciences and computational procedures. It is realized only after it is set in and is not known when it is likely to withdraw. A long way one has to travel to predict its occurrence, spread and its continuation to the next season over a region. The existing net work of observational set up in developing countries in Africa, Asia and in South America need to be strengthened further for effective monitoring of significant weather events at regional and micro regional level. With the rapid expansion of communication system over the past two decades, establishment of Automatic Weather Stations (AWS) at as many locations as possible even in remote regions should be taken up on priority basis and funding may be provided by the respective governments or by the International Organizations where ever necessary. Nations with limited resources may also be convinced to strengthen their weather observational net work in view of the increased occurrences of climate extremes and changing climate. Drought vulnerability regions over the globe were delineated based on sparse historical weather data which do not match with real surface conditions. Now, with the availability of weather data from more number of stations both temporally and spatially, drought prone regions over the world may be re-delineated. This would help the planners to allocate funds rationally to the affected regions. Globally every year, some regions or others may be experiencing droughts and more so in drought prone regions.

Soil pores differ greatly in size, shape, tortuosity, and continuity. They are characterized generally in terms of total porosity, air-filled porosity, and pore-size distribution. The characterization of pore space is important in understanding the storage and movement of water and gases, the development of plant root systems, the flow and retention of heat, and soil strength. The observation that bulk density is considerably lower than the average particle density indicates that only part of the bulk volume is occupied by soil solids and the remainder is occupied by a lighter material, such as air and water.

Total Porosity

Total porosity (n) is the percentage of the bulk volume not occupied by solids and can be computed using following relationship:

Remote sensing has proved its credibility beyond doubt in natural resources survey and environmental monitoring owing to its synoptivity, multispectral photographic capability and repetitive coverage. While its synoptivity gives unbiased information on the regional panorama of the earth surface, its multispectral possibility aids precise interpretation of various objects, as different terrestrial objects exhibit various spectral responses in different bands of the electromagnetic spectrum. Amongst various terrestrial objects, water has a characteristic spectral response of its own, i.e. it permits the blue / red part of EMR (electromagnetic radiation, 0.4-0.8 µm) to penetrate inside. On the contrary, it totally absorbs the infrared part of EMR (0.8-1.5 µm). As such blue/red part of EMR penetrates the water bodies, the impurities and suspended sediments are seen very clearly in various shades of gray as and when the water bodies are shallow. Many workers, therefore, have used blue / red band of the satellite data in such water-quality studies^l-3. Hardy⁴ has observed that the infrared light in the spectral regions of 0.6-1.4 µm has the potential to map the turbidity in the ocean water, whereas Kritakos et al ⁵ have used the rationed data of visible and near infrared bands (0.4-1.1 µm) and obtained better results for water quality monitoring. Keeping such facts in mind, the blue/red band (band 2) of the IRS 1A satellite data was used to configurate the bathymetry along Madras coast in Bay of Bengal (Figure 1 a).

In the present study, the IRS lA band 2 data (0.52-0.59 µm) of March 1991 was used and subjected to edge enhancement studies for the coastal zone of Madras (Figure 1 a). Such edge enhancement normally sharpens the edges of two contrasting objects or sharpens the edges of objects of contrasting relief. In such edge enhanced data, few

Tensiometer is a device to measure soil moisture tension or equivalent negative pressure of water in the soil. A tensiometer consists of a tube sealed at one end by a porous ceramic cup which is in contact with the soil and a vacuum gauge or a manometer connected at the other end above the soil surface. When the tensiometer is filled with water, the manometer or gauge will read zero tension. When such a tensiometer is placed in an unsaturated soil, the soil in contact with the porous ceramic cup will immediately start sucking water through the porous cup wall. The water in the soil pores immediately establishes hydraulic equilibrium with the water in the cup through saturated pores of the cup wall. Water and solutes can f low through the pores of the cup wall but not the air within the working range of the tensiometer. Water could be sucked from the tensiometer by the soil until vacuum created inside the tensiometer is just sufficient to overcome the suction of the soil. At equilibrium, the tensiometer reads directly the amount of soil suction. The outf low of water from the cup is very little. The effective range of the tensiometer is 0 to 0.85 bars depending on quality of the porous cup.

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.

As water enters the soil, air is displaced and the soil pores in the upper part of the profile become saturated. A continuous supply of water leads to an increasing depth of saturation. If the supply of water at the soil surface is cut off then the rapid downward movement of water may essentially ceased within 48 hours. The soil is then said to be at its field capacity. At this stage macropores are drained off but micropores are still filled with water for use by plants. Since it is difficult to draw a boundary line between macro-and micropores and there is no sudden change in the profile drainage rate for many soils, it is not easy to specify a depth and time after which soil water movement is negligible. Therefore, measurements are necessary in each soil to specify the time and depth of sampling after wetting. Special care would be necessary in soils with impeded drainage and sand lenses, which produce perched water tables.

Water holding capacity of soil is the amount of water that a given soil can hold against the force of gravity. Soil texture and organic matter are the key components that determine the water holding capacity of a soil. Soils with smaller particle sizes (silt and clay) have larger surface area and can hold more water as compared to sand which has large particle sizes and smaller surface area. It is an important hydro-physical characteristic of a soil because it provides simple means of determining useful moisture levels to maintain soil for good plant growth. Detail procedure for determination of water holding capacity of soil using Keen box method (Piper, 1966) is described here.

Hydraulic conductivity is an important soil property that determines the ability of a soil to transmit water. A method of measuring hydraulic conductivity of saturated soil using undisturbed soil core is described in this exercise.

Principle

Flow of water across a soil layer or a sample of known dimension can be best described by Darcy’s law expressed as:

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.

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

Infiltration rate refers to the volume of water entering into the soil per unit area in the unit time, when the soil is subjected to a shallow depth of ponding at the surface. Under continued ponding, the high infiltration rate in the beginning decreases to a constant value, known as final infiltration rate. The reduction in infiltration rate is due to combined effects of reduced hydraulic gradients, dispersion of aggregates, blocking of pores, cracks and channels, and swelling of colloids. Numerous techniques for measurement of infiltration rate have been developed to meet specific needs but use of double-ring infiltrometer has given consistent result in a variety of conditions.

Principle

In double-ring infiltrometer method, a small representative area in the field is bounded by two concentric metal rings (Figure 17.1) which permit impounding of water over the soil within the rings. The rate fall of surface of water ponded on the soil in the inner ring is taken as the rate of water intake or infiltration rate. In the cropped field, infiltration rate can be measured only within the rows and for which the diameter of the cylinders may be changed to meet the specific needs. The measurements under wetland conditions should be made from a distance of about 40-50 cm to avoid pressure effects.

14.1 What is Education

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

Soil aeration signifies the ability of a soil to supply oxygen to actively growing roots and soil organisms. Because of constant biological activity causing oxygen consumption and carbon dioxide evolution, the oxygen present in a soil pore or oxygen renewal by mass flow becomes inadequate to meet the plant demand. A continuous diffusion of oxygen from atmosphere to soil and to plant roots through the wetted pores plays an important role. The oxygen reaching plant roots has to diffuse not only through the gaseous phase in the soil pore and wetted pore neck but also through a water film that is present on the hydrated root surface.Lemon and Erickson (1952) suggested a platinum microelectrode method that simulates the field situation. In this method measurement of the rate of oxygen diffusing through the liquid phase to a reducing surface similar to the plant root.