eChapters

After doing all hard work during fruit production the last operation is harvesting on field. Though it is last operation, it should be done very carefully to get the quality harvest. Harvesting of fruits mainly depends upon the nature of fruit. Here nature refers to the classes of fruits divided on the basis of their respiratory pattern and ethylene production. On the basis of the respiratory pattern the fruits can be divided in to two categories, first one is climacteric and the second one is non climacteric.

1. Climacteric fruits: The meaning of word „climacteric is a critical period or event. Here, climacteric refers to the event of respiratory rise before the ripening phase. Those fruits which show such patterns are known as climacteric fruits (Taiz and Zeiger, 2002) Examples: Mango, guava, apple, banana, sapota, papaya, peach, pear, plum, fig, Annona.
2. Non climacteric fruits: Non climacteric fruits do not exhibit the respiration and ethylene production rise (Taiz and Zeiger, 2002). Examples: Citrus, grapes, pineapple, pomegranate, litchi, ber, jamun, cashew, cherry, strawberry.

The packing methods practiced by nurserymen for transport of nursery plants to distant places in India are neither uniform nor efficient. In different parts of the country, various practices are followed which are claimed to have been evolved by long experience of the local nurserymen. They vary according to nature of the plant, the season and the cheapest packing material available at the time of packing.

In many parts of the country, citrus nurserymen uproot plants, tie them in large bundles (with or without soil), keeping the plant tops exposed to air and roots tightly packed or tied in the gunny cloth. The pomegranate and guava plants prepared by air layering are packed as such if they are not already potted in small pots.

Many nurserymen pack the rooted or newly lifted plants in a ball of sticky clay. The ball of earth is then covered with grass and tied as firmly as possible, thus securing the roots against drying. A number of plants, thus prepared, are filled closely in light locally knit bamboo baskets. The baskets are covered thinly with coconut leaves as protection against injury during railway shipment. Mango grafts in pots are packed in light baskets with some cushion of grass to reduce the impact while loading and unloading the parcels on their long journey by rail and road.

Some nursery men use large baskets, woven out of coconut leaves with limp walls or sides. Plants such as coconut, chikoo, guava, mango are packed tightly in these baskets and shipped by truck or rail. This packing is done irrespective of plant containers such as pot or a ball of earth, with or without grass covering. The plants packed in all such fashions are usually damaged and some of them do not survive, unless care is taken during or after transplanting them in the permanent places. For better success, it should be seen that the roots of grown up plants do not get irreparable injury while removing from the bed or the pot. During transport, loss of water by transpiration should be kept at minimum, while the plants are awaiting dispatch or delivery at the railway platform, precaution should be taken against pilferage or damage by animals.

Plant Growth Regulator (PGR) are diverse group of organic compound other than nutrients, produced artificially or by plants which in low concentrations promote, inhibit or modify the physiological process in plant. Among the PGRs produced by plants are auxins (indole-3-acetic acid and its derivatives), gibberellins, cytokinins, abscisic acid and ethylene.

Application of certain plant growth regulators promotes the process of seed germination, and development of roots in cuttings and layers. Various growth regulators have been used with striking success. Of these auxins such as indole3-acetic acid (IAA), indolebutyric acid (IBA) and naphthalene acetic acid (NAA) have the greatest effect on root formation in cuttings and layers. These chemicals speed up the healing of the wound, induce more roots and their development. They are now used universally in the propagation of many fruit plants. The growth regulators are effective in minute concentration and are usually applied in dilute solutions and dust formulations or rarely in grease bases such as lanolin. Plant growth regulators are generally calculated in the form of parts per million (ppm) or microgram per gram (mg/g).

There are several planting plans or systems which can be adopted for planting an orchard. The main principle for the layout of orchard is:

1. It should accommodate maximum number of plant per unit area.
2. Provide adequate space for the development of the tree.
3. Ensure convenience in orchard operations.

The various lay out systems used are the following

Water is an important input in crop production. It acts as solvent, reactant and used for transpiration and maintaining cell turgidity. Hence, knowledge of soil moisture is essential for making irrigation scheduling. For determining soil moisture status, the commonly used methods and instruments are discussed along with their advantages and disadvantages. The soil moisture can be measured by determining either the soil water content or the soil water potential. The measurement of soil water content is an estimation of the mass or volume of water in the soil, while the soil water potential is an expression of the soil water energy status. The relation between content and potential is not universal and depends on the characteristics of the local soil, such as soil density and soil texture. We can measure soil moisture content both by direct and indirect methods. In direct method, we remove the water from the soil sample by evaporation and the amount removed is determined. This method is popularly known as gravimetric method. We measure property of soil that is affected by soil water content under the indirect methods. Indirect methods employ tensiometric, nuclear (neutron and gamma radiations), electromagnetic (radar and time domain reflectometers), hygrometric (electrical resistance, capacitance, Infrared absorption) techniques besides remote sensing for making soil water models. In the following paragraphs both the methods of soil water measurement has been discussed.

Alternate bearing (AB) or biennial bearing (BB) is a major challenge to growers and traders of fruit crops. It is typically initiated by an abnormally heavy crop in trees (on year), followed by a light or no subsequent crop (off year).When on and off year sequence does not follow a systematic pattern it is called periodicity of cropping or irregular bearing. Alternate bearing is assigned due to genetic factor while irregular bearing may be due to lack of good orchard management practices. Alternation becomes entrained and difficult to change unless severe climatic events intervene, or drastic management interventions are made. A heavy “on” crop results in reduced vegetative shoot and root flushing, and less carbohydrate (energy reserves) build-up. Phenomenon of alternation is more prominent in the perennial fruit crops particularly in Anacardiacae (mango and pistachio), Carylaceae (Hazelnut), Oleaceae (olives), Rosaceae (apple, pear, plums, apricot etc), Rutaceae (orange, Tangor, Satsuma etc) and also tamarind, jamun etc. fruit crops. Within a tree species some cultivars are regular while others are alternate bearer e.g. in mango Amrapali is regular while Langra is strongly alternate bearer.

1. INTRODUCTION

Increasingly, in recent years, we hear of new technologies for the production of clean energy or, as they say now in common usage, from renewable energy sources, there are many sources of renewable energy, but certainly the ones that deserve special attention are those derived from algae. Today, thanks to innovative systems called photobioreactors, you have a way to start producing, though unfortunately still a small part, the amount of clean energy from algae and various biological processes that develop. The photobioreactor is one of the most innovative systems of the 21st century, and is paving the way for a new concept of energy utilization , although the fossil fuel (oil of course) continues to lead the way, even if you are aware of the drastic and continuous decrease the world’s resources. Although still under investigation, but there are many aspects that allow, thanks to special engineering studies , already now create systems suitable for the production of energy directly from algae , while biofuels obtained from the latter, there are several studies and tests , which aim to further lower production costs, in order to bring them at par or even below the threshold of current fossil fuels. In addition, these photo bioreactors, allow to produce, under controlled conditions, products and raw materials from the algae for food and non-food market, often providing a viable substitute, nutritious and natural, to all those raw materials that are harmful to human health and animals, especially in the food and health sectors.

Blood Sample collection

Blood samples (5 ml per goat) will be collected aseptically from the jugular vein in a vacutainer tube (B.D. Bioscience, Germany) containing EDTA as anticoagulant and transferred to the laboratory in an ice box.

Isolation of Genomic DNA

The Genomic DNA will be isolated from the blood samples by ‘Phenol: chloroform isolation’ method as described by Sambrook and Russel (2001). The steps for isolation of genomic DNA are as follows:

7.1 INTRODUCTION

Web technology revolutionised information technology and GIS of no exception. Analysis of maps available in internet through remote personal computer is called as web GIS. The term web is GIS synonymous with the term internet GIS. Most of the software vendors in the field of GIS have developed their GIS compatible to internet. The advantage of internet GIS is no need to own a GIS software in the personal computer. Maps available in a web site can be analysed for GIS functions as one could do with GIS in standalone personal computer. Applications of web GIS is not limited. Most of the governmental agencies, business people and others put their data in their server and the data could be analysed spatially for the users requirement. Internet mapping is simple, cost effective and reach vast audience.

Internet GIS is useful in field like civil engineering, government organisations, forestry, environment, goescience, utility planning etc.

Lymph vessels arise from mesoderm by vasculogenesis and angiogenesis in common with the arteries and veins. Initially six primary lymph sacs develop in the late embryonic period. They are paired jugular sacs lateral to the internal jugular veins, a single retroperitoneal sac developing close to the root of the mesentry, the cisterna chyli dorsal to the retroperitoneal sac and a pair of iliac sacs at the junction of the iliac veins.

Lymphatic vessels draining the head, neck and fore limbs arise from jugular sacs. Drainage of lymph from the pelvic region and hind limbs is through the iliac sacs, while the retroperitoneal sac and cisterna chyli drain the viscera. At a later stage of lymphatic development, the lymph sacs become interconnected by a series of lymphatic vessels.The plexus between the jugular sacs and the cisterna chyli gives rise to the thoracic duct which opens into the jugular veins.

lymphatic organs : The lymphatic organs are fully developed and functional before birth. Immunocompetent cells can be detected in most lymphatic organs by the end of the second trimester of gestation.

lymphnodes : The lymphnodes are formed by the partitioning of small lymph vessels or sacs. Therefore, lymphnodes are usually found in related groups or in chains along the course of a lymph vessel. The partitioning is initiated by the ingrowth of mesenchymal processes into the lymph vessel. The mesenchyme forms a network of lymph sinusoids that communicate with the lumen of the lymph vessel. The mesenchyme also forms a reticular fiber frame work that outlines and supports the sinusoidal network. At this time a blood vessel enters the developing lymphnode. The point of entrance establishes the location of the hilus. At the periphery of the node the mesenchyme condenses to form a capsule. The mammalian lymphnodes consists of cortical and medullary regions. The cortical parenchyma contains lymphnodules, while the central medullary region contains anastomosing cords of lymphoid tissue. The structure of the porcine lymphnode differs from other domestic animals in that the lymphnodules are centrally located with the cords at the periphery. The flow of lymph in the porcine lymphnode is in the opposite direction to that in other domestic animals, with lymph entering at the hilus and leaving from the cortex.

The integumentary system comprises the skin its hair and glands and modified cutaneous structures hooves, claws, horns, beak and feathers. Although the mammary gland is a skin derived organ, because of its close association with the female genital system it is included in respective chapter. The skin consists of two layers: a superficial layer, the epidermis, which is derived from ectoderm and a deeper layer, the dermis, which develops from mesoderm.

Epidermis : The epidermal layer covering the entire embryo initially consists of a single layer of cuboidal cells resting on a basal lamina. Shortly after neurulation, these ectodermally derived cells divide and give rise to a superficial layer of flattened cells, the periderm and underlying layer of cuboidal cells, the basal layer. Further, proliferation of the cells gives rise to an intermediate layer resulting in a multi-layered covering of epidermis. Cells of neural crest and mesodermal origin also contribute to the population of cells found in the skin.

This practical assignment is conceptualized and designed to acquire practical learning experience through various activities implemented by NGOs in improving the livelihood of the targeted group. The assignment also projects a clear picture about the objectives, structure, functioning and activities of NGOs.

PURPOSE

To make the students acquainted with the NGOs and their learning experience in rural development.

THEORETICAL ORIENTATION

A non-governmental organization (NGO) is a not-for-profit organization that is independent from states and international governmental organizations. They are usually funded by donations but some avoid formal funding altogether and are run primarily by volunteers. NGOs are highly diverse groups of organizations engaged in a wide range of activities, and take different forms in different parts of the world.

This practical assignment is conceptualized and operationalized to study the settlement pattern, social stratification system, family resource base, ongoing development programmes and SHG of SGSY.

PURPOSE

To acquaint students with the first-hand knowledge about the village pattern and the on-going developmental programmes.
 To study about the extension programmes like SHG of SGSY and their structure and function.

This practical assignment deals with preparation of village improvement plan by analyzing the facts such as farming system, infrastructure, communication etc., facilities available at that particular village through participatory extension tools and methods. This assignment also helps students in designing a blueprint for developing the village into a model village.

PURPOSE

To develop the village in every aspect like agriculture, education, infrastructure, communication.

To prepare a comprehensive, realistic and practical blueprint for development of the village into a model village.

To improve the socio-economic condition of the farmer

This practical assignment is dealt with background and nature of Mahatma Gandhi National Rural Employment Guarantee Programme MGNREGP works and students will gain first-hand information and will evaluate this programme in this assignment.

PURPOSE

To acquaint students with the first-hand knowledge about the work carried out in MGNREGP and how it progress.

To know the socio-economic background of the MGNREGP workers and nature of economic activities available in the villages under MGNREGP.

This practical assignment is designed for the students to give first-hand information on components, working procedure and handling of public address system (PAS) and liquid crystal display (LCD) projector.

PURPOSE

 To acquaint students with how to operate and handle the public address system.

 To acquaint the students handle LCD projector.

This practical assignment is related to write the technical matters in simplest form to be digested by the common readers. It also helps in summarizing the entire matter related to new technology or innovation in a nutshell.

PURPOSE

 To acquaint the students how to write summary of a topic

 To improve technical writing skills

This practical assignment is related with indexing, footnote and bibliographic procedures for writing research articles, this assignment provides hands on experiences for the students on working with indexing, footnote and bibliographic procedures which eventually helps them during writing research articles.

PURPOSE

To make the students acquainted how to write indexing, footnote and bibliographic procedures.

1. Footnotes

Footnotes have a pronounced effect on style, general tone and clarity. Every footnote is a disgression from the main stream of thought. It interrupts the reader. If he reads it, his eyes must make an excursion to the bottom of the page; and when he is through, he must find the place where he departed from it. Lengthy footnotes can cause the reader to lose the thread of your message, to miss what you are trying to tell him.

It is of two types.

This practical assignment is dealt with collection, collation and maintenance of field and lab related information in a single compendium or diary.

PURPOSE

To make the students acquainted with the field diary and lab record

THEORETICAL ORIENTATION

Field Diary

There are two kinds of field notes

This practical assignment deals with identification of emerging enterprises in agricultural sector and helps students in identifying the emerging enterprises suitable for the study area on the basis of the situational analysis.

PURPOSE

 To provide a comprehensive idea about different enterprises.

 To acquaint the students with different factors which are essential for identifying emerging enterprises in agricultural sector.

This practical assignment deals with cost benefit analysis, and gives a clear picture of concepts of cost benefit analysis in determining the worth of an enterprise.

PURPOSE

 To make the students familiar with the concept of cost benefit analysis in determining the worth of an enterprise.

 To impart the knowledge and skill required to compute the cost benefit analysis process effectively for assessing the economic viability of an enterprise.

Introduction

Yeast contain a hard cell wall. Spheroplasts are yeast cells where the cell wall has been enzymatically degraded. These spheroplasts are very fragile so we must be careful with them. Once we have spheroplasts it will be very easy to lyse the yeast cells and quickly release the RNA and proteins in the cell into a controlled environment where we can temporarly keep the cellular RNases from degrading the RNA. We don’t want to lyse the cells before they are in this controlled environment.

Growth of Yeast Cultures

Cultures of wild-type and yeast containing various mutations will be grown up the day of the experiment. Each section will be given one wild type yeast culture and a culture containing one of the mutant varieties that we have discussed in class.

Yeast are grown very similarly to bacteria. Like bacteria, they have different stages of growth. Scientists divide these stages of growth into early-log phase, mid log-phase, late log-phase, and the stationary phase. These phases are based on the amount of yeast that are around in the broth and how quickly they are able to grow and divide based on nutrient use. Reading the absorbance of the sample at 600 nm is a way in which you can determine what phase of the yeast growth series you are in and how many cells you have.

Haploid yeast cells contain approximatley 1.2 pg of RNA per cell

Predict approximatly how much RNA you should isolate

Introduction

DNA denaturation, also called DNA melting, is the process by which double-stranded deoxyribonucleic acid unwinds and separates into single-stranded strands during the breaking of hydrogen bonding between the bases. Both terms are used to refer to the process as it occurs when a mixture is heated, although “denaturation” can also refer to the separation of DNA strands induced by chemicals like urea. For multiple copies of DNA molecules, the melting temperature (T_m) is defined as the temperature at which half of the DNA strands are in the double-helical state and half are in the “random-coil” states. The melting temperature depends on both the length of the molecule, and the specific nucleotide sequence composition of that molecule.

Applications of DNA Denaturation

The process of DNA denaturation can be used to analyze some aspects of DNA. Because cytosine / guanine base-pairing is generally stronger than adenosine / thymine base-pairing, the amount of cytosine and guanine in a genome (called the “GC content”) can be estimated by measuring the temperature at which the genomic DNA melts. Elevated temperatures are associated with high GC content. GC ratios within a genome are found to be markedly variable. These variations in GC ratio within a genome of higher organisms results in a mosaic like formation with islet regions called isochores. This results in the variations in staining intensity in the chromosomes. The isochores include in them essential protein coding genes, termed housekeeping genes and thus determination of ratio of these specific regions contributes in mapping these essential genesbacterial systematics has recommended use of GC ratios in higher level hierarchical classification. For example, the Actinobacteria are characterised as “high GC-content bacteria”. In Streptomyces coelicolor A3(2), GC content is 72%. The GC-content of Yeast (Saccharomyces cerevisiae) is 38%, and that of another common model organism Thale Cress is 36%. Because of the nature of the genetic code, it is virtually impossible for an organism to have a genome with a GC-content approaching either 0% or 100%. A species with an extremely low GC-content is Plasmodium falciparum (GC% = ~20%), and it is usually common to refer to such examples as being AT-rich instead of GC-poor.

To Estimate the DNA Using Diphenylamine

Introduction

DNA estimation is helpful to know about the total amount of DNA of prokaryotic as well as eukaryotic system. One method used for DNA estimation is Diphenylamine assay, is that of Burton who modified the original procedure of Dische. This procedure is based on treatment of nucleic acid with hot perchloric acid to hydrolyze DNA nucleotides. Diphenylamine reacts specifically with deoxyribose in DNA to form a blue-colored complex. Since diphenylamine does not react with ribose, one can assay for DNA in the presence of contaminating RNA.

Principle

The DPA method is based on the colorimetry measurement of products formed by the reaction of ù- hydroxylevulinaldehyde (from the deoxyribose released after depurination of DNA) with diphenylamine in 2.5 N perchloric acid.

When DNA is treated with diphenylamine under acidic condition (PCA) a blue complex is formed with a sharp absorption maximum at 595 nm (600 nm). In acid solution, the straight chain form of the deoxypentose is converted to highly reactive ω – hydroxylevulinaldehyde that reacts with diphenylamine to give blue complex. The reaction yields two mixture of product which together have absorbance maximum at 595 nm (600 nm). Interferences include proteins, lipids, saccharides and RNA. In DNA the only deoxyribose of the purine nucleotides reacts, so that the value obtained represents half of the total deoxyribose present.

DNA can be easily isolated and purified after size selection on an agarose gel. The fragment of interest is simply cut out of the gel with a razor blade and purified by a number of different methods.The easiest is to use a method that involves first dissolving the agarose slice in a solution at 50°C, then binding the DNA from the melted agarose to a silica-gel membrane.

Principle

In this method following gel electrophoresis using low gelling/ melting temperature agarose, the band of interest is removed from the gel. The agarose slice is then melted and subjected to phenol extraction.

To Prepare the Competent Cell and Carry Out Transformation Introduction

Transformation results from the uptake of purified DNA by bacterial cells and is the most frequently used procedure for introducing recombinant DNA molecules into bacteria. It is now widely used to transfer small plasmids from one bacterial strain to another. DNA is extracted from donor cell and used to treat the recipient cells that have been rendered more susceptible to DNA uptake. These competent cells allow DNA to enter through pores or channels in the cell membrane and in the case of plasmids, permit subsequent plasmid replication.

Introduction

Genetic variability is essential for the evolutionary success of all organisms. In diploid eukaryotic the processes of crossing over exchange of genetic material between homologous chromosomes and meiosis contributes to his variability. In haploid, asexually reproducing prokaryotic organisms, genetic recombination may occur by conjugation transduction, and transformation. In this experiment only the process of conjugation is considered.

Conjugation is a matting process during which a one direction transfer of genetic material occurs at physical contact between two sexually differentiated cell types. This differentiation or existence of different mating strains in some bacteria, is determined by the presence of a fertility factor of F factor, within the cell. Cells that lack the F factor are recipients (females) of the genetic material during conjugation and are designated as F^- . cells possessing the F factor have ability to act as genetic donors (males)during the mating. If this F factor is extra chromosomal (a Plasmid or episome), the cells are designated as F⁺; most commonly only the F factor is transferred during conjugation. If this factor becomes incorporated into the bacterial chromosome there is a transfer of chromosomal genes, although generally not involving the entire chromosome or the F factor. The resulting cells are designated as Hfr, for high frequency recombinants.

Introduction

Mutation refers to any heritable change in the base sequence of a DNA molecule. A mutagen is a physical of chemical agent that causes mutations to occur (or increase the frequency of their occurrence). Mutagenesis is the process of producing a mutation. If the mutation occurs in nature without the addition of a mutagen, it is referred as a spontaneous mutation, and the resulting mutants are spontaneous mutants. If it caused by a mutagen, the process is induced mutagenesis.

Ultraviolet light is a fairly potent mutagen. The main DNA lesions are two chemically different types of covalent dimers: cyclobutane-pyrimidine dimers and pyrimidine dimers. The pyrimidine dimers only account for 20% of the total dimers but are correspondingly more mutagenic. In E. coli the number of mutants induced by ultraviolet (UV) light can be reduced by exposure to visible light (photoreactivation), which implicates cyclobutane pyrimidine dimers since dimers can not be photoreactivated.

Aromatic amino acid of proteins, and purine as well as and pyrimidine bases of nucleic acid absorb ultra violet radiation. Pyridine bases, particularly thymine of DNA is the main target compound involved in bactericidal action of ultra violet radiation. The energy absorbed by thymine causes it to under go a photochemical reaction with adjacent ( adjoining) thymine molecule in same DNA strand. DNA replication is blocked because the formation of thymine: thymine (T:T) dimmers. As the dosage increase, cytosine-thymine (C:T) to (C:C) cytosine-cytosine dimmers can be found to add the lethality of ultra violate radiation.

To isolate a streptomycin resistant mutant of E.coli by Direct selection using Gradient Plate Method.

Introduction

Zylbalskii devised this technique.

A mutation is any change in the nucleotide sequence of DNA. These changes are heritable. Although most mutations are harmful to the organism, a small percentage is beneficial under certain environmental conditions. Mutation can occur during chromosome duplication and they may be spontaneous of they may be induced by mutagenic agent. In this experiment, we select for a mutation causing streptomycin resistance in E. coli. Resistant mutants will be detected directly using thy gradient plate method.

Principle

Microbiologist developed a highly efficient method for isolation of antibiotic resistant mutant. The gradient is said as gradient of antibiotic formed on an agar plate. A gene imparting resistant toward an antibiotic is present in plasmid or chromosome. The occurrence of mutant with different level of streptomycin resistant involves mutation of gene with unequal potential. This means that under certain cells degree of mutation is more while few shows less mutation. Some cells show intermediate resistant while others show completes resistant. The resistant in cell against streptomycin of this type, while in case of penicillin resistant increases step arise & so resistant mutant of high concentration of penicillin cannot be isolated/ obtained. While it is possible with streptomycin obtaining high resistance to penicillin stepwise & so this stepwise increase in resistance involves mutation of gene with equal potential. This theory of mutation through multi step procedure. The gene direct the organism to produce an enzyme, which inactivates an antibiotic & thus resistance to antibiotic, is observed in case of cells. Resistance of antibiotic is a plasmid-mediated resistance.

Precise collection and processing of soil sample is the first and foremost step for carrying out any soil study, therefore it is essential to collect the coil sample very accurately keeping in view the variations in slope, colour and texture of the soil management aspects. Soil sampling should be avoided from non-representative sites like recently fertilized plots, bunds, channels, marshy tracts and spots near trees, wells, compost piles etc. It should be kept in mind that erroneous samples will never yield accurate result in spite of very improved method of analysis. The depth of sampling may vary according to the need of soil study and extent of rhizosphere. However, in general the sampling depth for field crops is the plough layer (0 - 15 cm) but it could be up to one meter or as per the purpose of the study. Soil samples in dry farming areas should be taken depth wise as the roots of the crops in this conditions reaches to deeper layers in search of water and nutrients.

Mainly two types of soil samples (disturbed and undisturbed) are used for determining the physical properties of soil. The disturbed soil samples are used for determination of particle size distribution, particle density, aggregation, column studies for diffusion-dispersion coefficients and soil-water diffusivity. Whereas, undisturbed (core) soil samples are used for the estimation of bulk density, porosity, retention and transmission characteristics of air and water.

Bulk density is the ratio of oven-dry mass of soil to its total volume before drying. Knowledge of bulk density is useful in calculating moisture content by volume, porosity using particle density, volume of a known weight of soil, and weight of a furrow-slice. Bulk density is a direct measure of soil compaction. Bulk density is highly dependent on any kind of physical manipulation, degree of wetness, and kind and arrangement of soil particles. For this reason, preservation of original structure in the sample is most essential aspect of the methodology for determination of bulk density. Common methods of determining soil bulk density use soil cores or clods in their natural state.

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.

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:

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.

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:

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.

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.

Soil temperature plays an important role in plant growth. Solar radiation received on the earth surface raises the temperature of the soil surface from morning to solar noon followed by a decline until the next morning. Soil temperature gradients established on the surface lead to flow of heat downwards causing a rise in temperature of lower layers. These variations in temperature affect germination, emergence and further growth of plants. Several types of thermometers such as mercury or liquid in glass, bimetallic, bourdon gauge, thermocouples and electrical resistance have been used in soil research but the use of thermocouples and thermistors has been found most useful. A brief description of different types of thermometers used in measurement of soil temperature is given below:

Liquids in Glass Thermometer

A liquid-in-glass thermometer (Figure 20.1) consists of a capillary glass tube with a bulb at one end filled with a thermometric liquid (mercury), vacuumed and sealed. By reading the position of the liquid level on a scale the temperature value can be obtained.

Determination of pH is actually measurement of hydrogen ions activity in soil-water system. It is defined as negative logarithm of the hydrogen ion activity. Mathematically, it is expressed

as:pH = - log a H⁺

The pH value of a soil is an indication of soil reaction i.e. acidic, neutral or alkaline. The nutrient availability is governed by soil reaction. It is maximum at neutral pH and decreases with increase in acidity or alkalinity. Thus, pH value gives an idea about the availability of nutrients to plants.

Principle

The pH is a measure of hydrogen or hydroxyl ion activity of the soil-water system. It indicates whether the soil is acidic, neutral or alkaline in reaction. Since crop growth suffers much under both very low (strongly acidic) as well as very high pH (alkaline) conditions.

Now a days, most of the pH meters have single combined electrode. Before measuring the pH of the soil, the instrument has to be calibrated with standard buffer solution of known pH. Since, the pH is also affected by the temperature, hence, the pH meter should be adjusted to the temperature of the solution by temperature correction knob.

The method is based on the Stokes law which states that the rate of fall of particles in suspension is directly proportional to their size. Accordingly, larger particle (sand) will settle first, followed by silt and clay. The resistance offered by the liquid to the fall of the particles varies with the radius of the sphere.

Principle

This method is based on the principle of dispersion and sedimentation techniques, employed to a given weight of soil sample. Mechanical stirring disperses macro aggregates while chemical dispersing required for micro aggregates. The mixture of dispersed soil particles in water is called a soil suspension. Sedimentation refers to the settling rates of the dispersed particles in water, which is a function of particle size and is governed by Stoke’s law.

Purpose

The bulk density varies indirectly with total pore space present in the soil and gives a good estimate of porosity of soil. Bulk density is of great importance than particle density in understanding the physical condition of soil.

Soil bulk density is defined as the ratio of the mass of the oven dry soil to its bulk volume.

Method of determination

Different methods are available for bulk density determination which differ how the soil sample is obtained and its volume is determined such as core, clod and excavation methods. There are other methods for the determination of bulk density where different principles are employed, for example, radiation method. Commonly used methods are weighing bottle, core and clod method.

Soil aggregates refers to a group of two or more primary particles which cohere to each other more strongly than surrounding particles. Under field condition, all such units also cohere to some degree with neighboring aggregates and form larger aggregates. Such aggregates form and break easily into smaller aggregates during tillage and by disruptive action of water and air. The aggregates maintaining their identity are those in which the cohesive forces among particles are greater than the disruptive forces. A quantitative characterization of aggregates is done by determining aggregate stability and size distribution of aggregates. The aggregate stability refers to the resistance of soil aggregates to breakdown by water, air and mechanical manipulations.

The soil aggregates which can stand the disruptive forces of wetting by water are known as water stable aggregates. Therefore, the process of wetting, disruption of dry aggregates and screening of aggregates of different sizes should reasonably compare to the disruptive action of water and mechanical forces of tillage under wet conditions. The vacuum wetting of dry soil largely simulates the process of soil wetting in the surface layers but the immersion wetting is more comparable to the wetting of surface soil by irrigation. Similarly, sieving under water compares more closely with the disruptive action of water and other mechanical forces. The mean weight diameter (MWD) of water stable aggregates is a useful index to characterize the change in structure due to tillage. The mean weight diameter can be calculated using following equation.

The major part of soil nitrogen exists in complex combination in the organic compounds. It becomes available to plants after breakdown to simple form followed by mineralization. The chemical methods for determination of soil nitrogen availability involve either direct or indirect of total nitrogen or measurement of a fraction of easily hydrosable nitrogen by employing solution of dilute acid or alkali. Distillation of alkaline potassium permanganate solution has often been adopted for estimating the ox disable and reactive form of soil nitrogen. The available nitrogen in soil is determined by alkaline permanganate method as per procedure suggested by Subbiah and Asija (1956).

Principle

A known weight of the soil is mixed with alkaline potassium permanganate (KMnO₄) solution and distilled. The organic matter present in soil is oxidized by the nascent oxygen, liberated by potassium permanganate, in the presence of sodium hydroxide and the released ammonia is condensed and absorbed in known volume of a boric acid with mix indicator to form ammonium borate, the excess of which is titrated with a standard sulphuric acid.

Sulphur (S) occurs in different forms in soil viz., sulphites, sulphates , sulphides and in organic compounds. Plants absorb S in the form of sulphate(SO₄ ^2-) . The organic forms of S compounds become assimilable, especially following microbiological transformation into SO₄ ^2-. The mineralization of organic sulphur in a soil depends primarily upon the N:S ratio and any SO₄ ^2- formed may be fixed against extraction, particularly if much Fe and Ba is present or if soil is very acidic.

Principle

Beside some amount in the soil solution, available sulphur in mineral soils occurs mainly as adsorbed SO₄ ^2- ions. Both CaCl₂ and phosphate solutions (as monocalcium phosphate) are generally used for replacement of the adsorbed SO₄ ^2- ions. Use of Ca salts have a distinct advantage over those of Na or Na, as Ca prevents deflocculating in heavy textured soils and leads to easy filtration. SO₄ ^2- in the extract can be estimated turbid metrically using a spectrophotometer. Sulphur in the extract can also be measured by colorimetric method using barium chromate but the turbimertic method given below is mainly used in the soil testing laboratories.

Calcium (Ca) and magnesium (Mg) are the two most abundant alkaline earth cations in soils. They both occur as soluble ions in soil solution, exchangeable, non-exchangeable and in organic material. Soils from arid regions are richer in Ca (1-2% CaO), while those from humid zones have a low content (0.01-0.02% CaO). On the other hand exchangeable Mg is found in very small quantities in calcareous soils. Sometimes, in acid soils, Mg²⁺ represents the largest quantity of the sum of exchangeable bases.

Principle

The method is based on the principle that calcium, magnesium and a number of other cations form stable complexes with versenate (ethylendiaminetetraacetic acid disodium salt, EDTA) at different pH. A known volume of standard calcium solution is titrated with standard 0.01N EDTA solution using murexide (ammonium purpurate) indicator in the presence of NaOH solution.

The end point is a change of color from orange red to purple at pH 12 when the whole of Ca forms a complex with EDTA. Calcium plus Mg are also present in the solution and can be titrated with 0.01N EDTA using buffer solution and a few drops Eriochrome Black T indicator. The end point is a change of color from red to blue at pH 10. Beyond pH 10, magnesium is not bound strongly to Erichrome Black-T indicator to give a distinct end point.

Boron occurs as anion in soils and isrequired by plants in very small quantity. Water soluble B makes the estimate of its availability to plants. Total boron in soils varies from 20 to 200 mg kg^-1 and available (water soluble) boron in soils ranges from 0.03 to 12 mg kg^-1 respectively. The threshold value ranging from 0.1 to 0.5 mg kg^-1 (water soluble B) depends upon the soil type, crops, and other factors, below which the response to applied boron may be expected. Its availability is affected by soil pH as under:

A pesticides residue is any substance or mixture of substances in food, agricultural commodities or animal feed resulting from the use of pesticides and includes any specified derivatives such as degradation products and impurities that are considered to be of toxicological significance.

Pesticide residue analysis (PRA) may be defined as the quantitative and qualitative analyses of the representative samples drawn from agricultural field, market and environment for pesticides and their toxic metabolites.

Chromatography is a physical method of separation in which components to be separated is distributed between two phases, one of which is stationary while other moves in a definite direction. By separating the sample into individual components, it is easier to identify (qualitative) and measure the amount (quantitative) of the various sample components. There are numerous chromatographic techniques and corresponding instruments.

Gas Liquid Chromatography (GLC) is the most widely used analytical technique for estimation of volatile and thermo stable type of pesticides with speed, accuracy, reproducibility and sensitivity.