eChapters

5.1 INTRODUCTION

One of the generalizations that can be made about soils is that the particles of which they are composed together have a nett negative charge. There are exceptions: for example, some iron- and aluminium-rich tropical soils can attain a positive charge at low enough pH, but such cases are rare. It is nonetheless a fact that most anions are held strongly by the soil complex, and it is the purpose of this chapter to look at some of the reasons why this is so. Historically, the impetus to research in this area has largely been the practical necessity to understand the behaviour of applied phosphate fertilizer, and it is some indication of the complexity of the problems involved that, even after decades of effort by soil chemists and agronomists, this understanding is still far from complete. The reason for this is partly that the soil surfaces themselves are, as has been described by Greenland and Mott (1978) in the companion volume, the product of a ‘dirty’ environment. This generally means that phosphate added to the system has to exchange on sorption with an inadequately characterized suite of anions presorbed on ill-defined surfaces. There are also in the case of phosphate, possibilities of simultaneous precipitation. Faced with these problems, the trend in the literature over the past ten years or so has been to investigate in detail the physical chemistry of the sorption of anions onto simple surfaces which are fairly well understood, in the expectation that this will lead to ultimate comprehension of behaviour in the natural system. The results of many relevant experiments have only recently been published, and so some parts of the account are still at the discussion stage in the literature. This is especially true of phosphate, which looks destined to be a joker in the anion pack for some time to come.

6.1 INTRODUCTION

This chapter is concerned with the interactions which retain mobile chemical species in the soil environment. Emphasis is centred on the binding of small organic chemicals to soil particles of colloidal dimensions, and on the associations between polymeric materials and inorganic colloids which strongly influence the physical and chemical behaviour of soils. These interactions are also involved in the retention by soil of water, discussed by Farmer (1978) in the companion volume to this book, and in ion and ligand exchange reactions, and in mass flow and diffusion discussed in preceding chapters.

The term colloidal refers to particles and discontinuities of matter (e.g. pore spaces or thin films) of dimensions in the range of 1 nm to 1 jxm (IUPAC, 1972). For such finely divided systems the properties of the interfaces are very important because these largely control the behaviour of the colloidal systems. The term phase is used to describe the homogeneous parts of a system and an interface or surface is the boundary region between any two phases; the relevant interfaces are solid/gas, solid/liquid, liquid/liquid, and liquid/vapour. Where none of the solid, liquid, or vapour phases in a system are finely divided the ratios of the interfacial areas to the bulk volumes of the phases are small, and the effects of the interface between neighbouring phases can be neglected.

The most extensive surfaces in soils are contained in domains and micro- aggregates of colloidal particles (cf. Greenland and Hayes, 1978; Greenland and Mott, 1978), These surfaces are accessible from the pore spaces between solid particles. Under normal field conditions these spaces remain filled with water. Thus, although modern fertilizers, and chemicals for the control of plant growth, pests, and diseases are applied to soils as solids, liquids, and gases, most of the interactions with the soil colloidal constituents take place at the solid/liquid interface. We shall be primarily concerned here with uptake from the liquid phase by solid soil components, although interactions at the solid/gas interface can sometimes be important.

7.1 INTRODUCTION

An understanding of the processes of oxidation and reduction in soils and the associated changes and practical implications requires a knowledge firstly of soil respiration and the movement of O₂ and CO₂ in soils, and secondly an appreciation of the significance of the changes which occur when, as a result of the use of all the O₂ in a given zone of the soil, respiration changes from aerobic to anaerobic. This results in marked changes in the biochemistry of the system. A basic knowledge is therefore needed of the microbiology and biochemistry of aerobic and anaerobic respiration and of the physics of gas movement, as well as of the chemistry of the system.

8.1 INTRODUCTION

The development of a soil profile involves the mobilization of major and minor elements and their subsequent deposition elsewhere in the profile or removal in the drainage water. For a full understanding of these processes we need to know what are the forms and reactivities of the soil constituents, the nature and mode of action of the mobilizing agents, the forms in which the mobilized material is transported—whether colloidal or in true solution, whether in ionic or complex form, whether alone or in association with other soil constituents—as well as its stability towards oxidation and reduction, microbial action, pH, and sorption and coprecipitation. The availability of micronutrients to plants is presumably governed by factors such as these. The current concern with problems of soil contamination has brought to the attention of soil chemists numerous toxic metals that were previously regarded as essentially the province of the geochemist.

It is probably true to say that no one of the factors listed above can be considered in isolation, but so far as any one factor is of dominant importance, this is nature of the mobilizing species; this determines the form in which the metal is transported, and its ultimate fate in the soil or in the drainage water.

This chapter is an attempt to summarize our present knowledge of the processes responsible for the mobilization and immobilization of metals in soils.

9.1 INTRODUCTION

The annual production of organic carbon by photosynthesis on land is about 6x 10¹⁰ tonnes (Table 9.1), most of which eventually decomposes on or in the top 50 cm of the soil. This organic matter can be in lumps as big as a mature oak tree (say 0.5xl0²m³) or as small as a bacterium (0.5 x 10~¹⁸m³). It can be in material as resistant to decay as oil palm nuts, which persist for years in soil in the humid tropics, or as transient as mammalian protein. Yet in the long run, no fraction of the organic matter in plants and animals can withstand decomposition to carbon dioxide and water. If this were not so, any completely resistant fraction would by now cover the surface of the earth. Although under normal conditions organic matter does not accumulate indefinitely in soil, exceptions can occur, as, for example, when a soil becomes permanently waterlogged. When a geologically stable surface has been under the same vegetation for a long time, the soil approaches steady state conditions, with the annual losses of organic matter balancing the annual input. Thereafter the organic matter content of the soil remains constant, until the next vegetational change or geological catastrophe. This process, in which losses and gains proceed simultaneously, is described as turnover and may be defined (for carbon) as ‘the flux of carbon through the organic carbon in a given sample of soil’. Turnover time is then the amount of carbon in the soil system (or part of that system) divided by the annual input of carbon into the system (or part of that system). Turnover and turnover time will be discussed more fully in Section 9.2.5.

10.1 INTRODUCTION

The fate of plant nutrients in fertilizers added to soils is to be: (1) taken up by crops; (2) retained by the soil; (3) removed in solution in drainage water; (4) lost as a gas; or (5) removed by erosion. These five processes are discussed in this chapter. The purpose of using fertilizers is to increase crop growth and they fail in this unless they are taken up by plants. Table 10.1 gives FAO (1972) data which show that large fertilizer use is restricted to the developed countries which use 65 times the amount used per hectare in developing countries. Within the group of ‘developed’ countries most of North-West Europe uses much fertilizer; outside of Europe large use per hectare is confined to a few countries such as Japan and USA. It is in the developed countries where much fertilizer is applied that efficient uptake of plant nutrients is already important to national economies, and where nutrients lost from agriculture cause eutrophication of natural waters and are regarded as pollutants.

11.1 INTRODUCTION

The heavy metals which, by definition, are elements having a density greater than five in their elemental form, comprise some 38 elements. However, the term usually, and here, refers to twelve metals that are used and discharged by industry, i.e. Cd, Cr, Co, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sn, Zn. Most of the present discussion will centre on those metals that may represent potential hazards to plants or animals; these are Cd, Cu, Hg, Ni, Pb, and Zn.

The heavy metals are widely distributed in the environment, in soils, in plants and animals and in most of their tissues. The concentrations of individual metals in living tissue are ordinarily very low and must be maintained within narrow limits to permit the optimum biological performance of most organisms. Some heavy metals are essential in trace amounts, namely Co, Cu, Fe, Mn, Mo, Zn for plants and, in addition, Cr, Ni, Sn for animals; Cd, Hg, and Pb, have not been shown to be essential for either plants or animals. Deficiencies of the essential metals have been frequently reported and substantial benefits have arisen from correcting these by addition to the soil and subsequent transfer from soil to plant is for most increasing concern about the entry into soil of some heavy metals and the possible adverse effects that they might have on plants and animals and, in turn, on human health. The main sources of these heavy metals are: (i) urban industrial aerosols, created by combustion of fuels, metal ore refining and other industrial processes; (ii) liquid and solid wastes from animals and man; (iii) mining wastes; or (iv) industrial and agricultural chemicals. Although in some circumstances there are direct atmospheric inputs to plants, addition to the soil and subsequent transfer from soil to plant is for most heavy metals the major route of entry into the living tissues of plants, animals, and man. The fate of heavy metals added to soils, including their mobility and reactions in the soil and their subsequent uptake and distribution in plants, is therefore of critical importance in relation to man’s health.

The use of sampling in making decisions about an aggregate (or population) is possibly as old as civilization itself. Sampling is first broadly classified into two categories known as subjective and objective. Any type of sampling which depends upon the personal judgement or discretion of the sampler himself, is called subjective sampling. But the sampling method which is governed by a sampling rule or is independent of the sampler’s own judgement is known as objective sampling. The main difficulty with subjective sampling is that the sampler is ignorant of the degree of representativeness of his sample or the accuracy of the final estimates of the population values obtained.

Objective sampling is further subdivided as non-probabilistic, probabilistic and mixed. In non-probabilistic objective sampling, there is a fixed sampling rule but there is no selection probability attached to the sampling unit e.g. selection of every 10th individual from a list, starting with the first, or selecting every 10th line in a paddy field. If however, the selection of the first individual is made in such a manner that each of the first 10 gets an equal chance of being selected, it becomes a case of mixed sampling, partly probabilistic and partly non-probabilistic). On the other hand, if for each individual unit there is a definite pre-assigned probability of being selected, the sampling is said to be probabilistic sampling.

2.1 Simple Random Sampling
The simplest and common most method of sampling is simple random sampling. In this procedure, the sample is drawn unit by unit with equal probability of selection for each unit at each draw. It is sometimes referred to as unrestricted random sampling.

3.1 Introduction
Out of all methods of sampling, the most commonly used procedure in surveys is the stratified random sampling. When population units are of heterogeneous nature and if we select a sample using SRSWOR scheme then the sample selected may not be the representative sample and the estimate worked out from that sample will not be the reliable estimate of the population parameter. The estimate of sampling variance of the sample estimator obtained from that sampling scheme may happen to be very high leading to get a less precise estimate of the parameter. In such type of population, to overcome these draw backs, we use another sampling scheme known as stratified random sampling which is defined as follows.

4.1 Introduction
In many surveys, information on an auxiliary (supplementary, ancillary or apriori) variable x, which is highly (positively or negatively)correlated with the variable y under study, is readily available and can be used for improving the sampling design. Stratified sampling and probability proportional to size (p.p.s) schemes are two examples of improved sampling designs, in which the use of data on auxiliary variable has been made. However in both the schemes, it implies that the information on auxiliary variable on individual sampling units is available prior to presentation of sampling design. In case, data on auxiliary variable for individual sampling units are not available but only the aggregate value for all units of auxiliary variable is available, the two schemes can not be used. In such a situation, the aggregate data on auxiliary variable can still be used at the time of estimation of parameters under consideration, provided the data on auxiliary variable for the sampled units can be easily obtained at the time of recording the values of the study variable. Such types of estimation are based on ratio, product, difference and regression methods of estimation.

5.1 Introduction
In random sampling it is assumed in prior that the population is divisible into a finite number of distinct and identifiable units and these units are known as sampling units. The smallest unit into which the population can be divide, is called an elementary unit (element) of the population. A group of such units is known as cluster. When such cluster is treated as sampling unit, then the sampling procedure adopted is known as cluster sampling. If the entire area containing the population under study is divided into smaller area segments and each element in the population belongs to one and only one such area segment, the sampling is sometimes known as area sampling.
Generally, identification and location of an element requires considerable time. However, once an element is located, the time taken for surveying a few neighbouring elements is small. Thus, the main function in cluster sampling is to specify clusters or to divide the population into appropriate number of clusters. Clusters are generally made up of neighbouring elements and hence elements within a cluster happen to be of similar nature. As a matter of fact, the number of elements in a cluster should be small and the number of clusters should be large. The required number of clusters can be selected either by equal or unequal probabilities of selection. All the units in the selected clusters are enumerated completely i.e. complete enumeration is made in all the selected clusters.

6.1 Introduction
So far we have considered the methods of sampling in which the successive units (elements or clusters) were selected with the help of random numbers. Now, we shall consider a new method of sample selection in which only the first unit of the sample is selected with the help of random number, the rest being selected automatically according to a predetermined pattern. The method is known as systematic sampling. It is operationally more convenient than simple random sampling and which at the same time ensures for each unit, equal probability of inclusion in the sample. The systematic sampling can also be termed as systematic random sampling because of the first unit of the sample being chosen randomly. The pattern usually followed in selecting a systematic sample is a simple pattern involving regular spacing of units.
Thus, suppose a population consists of N units and is serially numbered from 1 to N. Suppose further that N is expressable as the product of two integers k and n so that N=nk. Draw a random number i such that 1 < i < k and select the unit with the corresponding serial number and every kth unit in the population there after i.e. the sample consists the units bearing the serial numbers as

7.1 Introduction
In chapter 5, the cluster sampling has been discussed in which clusters were considered as sampling units and all the elements in the selected clusters were enumerated completely. It has been stated there that the cluster sampling is economical under certain circumstance but the method restricts the spread of sample over the population which results generally in increased sampling variance of the estimator under consideration. It is, therefore, logical to expect that the efficiency of the estimator will be increased by distributing the elements over a large numbers of clusters. Hence instead of observing all the units in the selected clusters, one may like to observe only few elements of the selected clusters. This will involve the sampling work to be done also within the selected clusters. If we do so, the process of selection will involve sampling work to be done at two stage, one for selecting the clusters where sampling units are the clusters and the second for selecting the units (elements) within the selected clusters where sampling units are the elements.
The process of sampling can be done at more than two stages. In this case the first stage unit will be larger than the second stage units and the second stage units will be larger than the third stage units and so on. Due to process of sampling in stages, such sampling is called “Multistage sampling.”

8.1 Introduction
We have already discussed in details how different sampling schemes can be employed to draw the representative samples suitable to many kinds of population whose sampling units differ in nature. From practical view points, however, it is often more important to be able to make decision about certain unknown characteristics of the population on the basis of informations available in the representative samples which are drawn from the parent populations. Such decisions taken, are known as the “Statistical decisions”. For example, we may wish to decide on the basis of sample data whether (i) One educational system is better than the other or not, (ii) A given six faced die is unbiased (balanced) or not, (iii) A new insecticide is really effective to control the attack of insects or not? etc. Such problems are dealt with in the theory of statistical decisions which uses the principles of sampling theory.

9.1 Introduction
In the preceeding chapter, we have studied the estimation part of statistical decision (inference) infered about the parameters of the population on the basis of information available in the sample observations drawn from the parent population under study. In the present chapter we discuss the problems related with the tests of statistical hypothesis and its significance about the population parameters under study. For understanding of the subject matter considered in this chapter, very clearly and easily, one must be familier with the statistical terminologies used in the subject matter. Hence we discuss the various notable terminologies with some suitable examples in a simple way for better understanding.

10.1 Normal Distribution
The normal distribution is the most widely used distribution in statistics. Almost all biological data including the agricultural data eg. crop yield, plant height, seed weight, seed size, protein percent in pulse, oil content in an oil seed etc are assumed to be normally distributed. In practice their distribution is rarely verified. In distribution theory, for large values of n, the number of trial (or sample size), almost all the distributions e.g. Binomial, poission, Negative binomial, chi square, student’s t, and Snedenor’s F distributions etc. are very closely approximated by normal distribution. It is a continuous distribution with mean and variance as its two parameters.

11.1 Introduction
In the preceding chapter 10, we have discussed in detail, the test procedures for which it has been assumed that the sample size n is large, (i.e n >,30). Those tests are also known as approximate tests or z tests. But in case when sample size n is small i.e. n<30, the approximate test fails to deal with such problem and we apply the theory of exact sample, for small sample tests. The exact sample tests however can be applied to large samples also though the converse is not plausible. In all the exact sample tests, the basic assumption is that the parent population is normally distributed.
In this part we will discusse in details the exact sample tests (based on exact sampling distributions namely snedekor’s F, student’s t and chi square (χ2) distributions. These distributions will be simply introduced in short because main emphasis has to be given only on the test procedures based on them.

12.1 Chi-Square Variate
The square of a standard normal variate is known as a chi – square variate or chi square statistic with one degree of freedom.

13.1 Introduction
In the previous chapters, we have considered different tests of significance based on normal distribution, F distribution, student’s t distribution and Chi-square (χ2) distribution which are frequently applied by the users of different disciplines of applied sciences and social sciences. In this chapter some more tests of significance are considered which have not been covered in those chapters. These tests are also based on t, F, Fisher’s z transformation, χ2 and some other test statistics are also discussed one by one in the following sections.

THEORY
    ·    Father of Extension: James Stuart
    ·    Word Extension: Derived from Latin roots “ex”    - Out
                                                              tensio”    - Stretching
    ·    Extension term originated in England as University Extension in 1866.
    ·    The term Extension Education first used in 1873 by Cambridge University.
    ·    Philosophy of Extension (Kelsey and Hearne, 1967): How to think.
    ·    Binet test: Intelligence test (IQ).
    ·    Function of Extension: Change in Attitude, Skill and Knowledge of an individuals.
    ·    Extension Education Process:  Extension education is a participative and continuous process.
    ·    Learning Situation: It is a condition or environment in which all the elements necessary for promoting learning are present. 
    ·    Elements of effective learning situations in Extension are:

Theory
The Constitution of India related to women:
    ·    Guarantees to all Indian women equality: Article 14
    ·    No discrimination by the State: Article 15(1)
    ·    Equality of opportunity: Article 16
    ·    Equal pay for equal work: Article 39(d)
    ·    Securing just and humane conditions of work and for maternity relief: Article 42
    ·    The All India Women’s Education Conference was held in Pune in 1927. 
    ·    The National Policy For the Empowerment of Women came was passed in 2001
    ·    In 2010 March 9, Rajya Sabha passed the Women’s Reservation Bill requiring that 33% of seats in India’s Parliament and state legislative bodies be reserved for women

Theory
    ·    Father of sociology: Auguste Comte 
    ·    The term sociology was coined by Auguste Comte (1789-1875).
    ·    Sociology word comes from two roots i.e.     
        Latin word ‘socius’ meaning companion         
        Greek word ‘logos’ meaning speech or reasoning.
    ·    Sociology: Sociology is the scientific study of human social behavior and its origins, development, organizations, and institutions. It is a social science that uses various methods of empirical investigation and critical analysis to develop a body of knowledge about human social actions, social structure and functions.

Theory

Research: The word research is composed of two words “Re” and “Search”.
“Re” - ‘Again or over again or a new’ 
“Search” - ‘To examine closely and carefully’ or ‘to test and try’. 
Research is a careful, systematic, patient study and investigation in some field of knowledge undertaken to establish principles / policies. 
Science: It is a systematized knowledge derived through observation, experimentation or any other systematic method or procedure in order to determine the nature of phenomenon or process being studied or the causes behind specific events.

Theory

Communication word comes from Latin ‘Communis’- Common
Communication: The communication is the process of human interaction in which one person communicates a message/idea to another person. 
Diffusion: It is the process by which an innovation/new idea/new technique spreads. 
According to Rogers (1983) ‘Communication is the process by which the message is transmitted from the source to the receiver’.

Theory

Extension Teaching Methods: Methods by using them new information can pass freely between the extension worker and rural communities. Extension education is mainly concerned with the dissemination of useful and practical information relating to rural life and helping the rural people in the practical application of such knowledge to rural situations. Extension teaching methods can be classified on the basis of:

Theory

Rural Development: The economic betterment of people as well as greater social transformation. The efforts for rural development comprises the direct and indirect involvement of people at the grass root level for development of agriculture/animal husbandry, industry, communication, education, health and allied sectors. 
Democratic Decentralization: To ensure people’s participation in rural development programmes, democratic decentralization has been the core principle of the government since 1957. In the process, people’s participation in all developmental activities has been the unique phenomena to find out the solutions of their problems.
Panchayat Raj: On the principle of democratic decentralization, Panchayat Raj institutions were launched in 1957 as per the recommendations of Balwant Rai Mehta Committee. Under this, the government has derived its authority from the people, and distribute to some extent to the people for decision and action at the local level called Panchayat Raj.

Theory

  The term ‘Management’ derived from word ‘manage’ derived from French word menage means ‘housekeeping’.

 According to Knootz and Weihrich 1988, ‘Management as the process of designing and maintaining an environment in which individuals, working together in groups, efficiently accomplish selected aims’. 

According to Louis E.Boone and David L.Kurtz ‘management as the use of people and other resources to accomplish objectives’.

POSDCORB is an acronym widely used in the field of Management and Public Administration., it first appeared in a 1937 staff paper by Luther Gulick and Lyndall Urwick. The acronym stands for steps in the administrative process: Planning, Organizing, Staffing, Directing, Coordinating, Reporting and Budgeting.

Theory

ICT or Information and Communications Technology: The basket of technologies, which assist or support in storage, processing and dissemination/ communication of data/information. ICT thus includes technologies such as desktop and laptop computers, software and connection to the Internet that are intended to fulfil information processing and communication functions.

ICT Tools

    •    Word processing applications - used for preparing text documents.
    •     Presentation software - used for preparing presentations
    •     Spreadsheets - used for calculation and preparing tabular data with calculations
    •     Databases - used to store the information in the form of records and retrieving information using query mechanism.
    •    Multimedia – used to organize the information more meaningful manner with the help of text, images, animation, audio and videos
    •    Web browsers and E-mail – used to searching information and sending or receiving mail using Internet.

Theory

Statistics: Collection of methods for planning experiments, obtaining data, and then organizing, summarizing, presenting, analyzing, interpreting, and drawing conclusions.

Sir R.A.Fisher: Father of modern statistics.

Population: All subjects possessing a common characteristic that is being studied.

Sample: A subgroup or subset of the population.

Parameter: Characteristic or measure obtained from a population.

Statistic: Characteristic or measure obtained from a sample.

Karl Pearson: Study of correlation and chi-square test of goodness of fit.

W.S.Gosset: Student’s t-test for small sample

Francis Galton: Regression analysis.

Taxonomy is the science of identifying (discovering), describing, naming and classifying organisms. It is a complex summing up of knowledge starting with thorough analysis to base the synthesis that will end up in the name of a taxon. Correct identification of biological taxa is a necessary prerequisite to all other enquiries about the biological world. Taxonomists attempt to divide the world of living things (biodiversity) into distinguishable entities (taxa-such as species, genera, and families), develop tools (e.g., identification keys) to allow others to recognize and identify these taxa, and organize the described taxa within a hierarchical classification system that reflects evolutionary relationships. The outcomes of taxonomy are, therefore, very practical in terms of providing tools to facilitate identification, an infrastructure for organizing biological information, and a universal language for communicating information about the identity and classification of biological entities. Thus, naming and ordering of objects into groups is probably the most fundamental step in the development of scientific principles. Taxonomy identifies and enumerates the components of biological diversity providing basic knowledge underpinning pest management (Ramaraju and Pratheep, 2008). 

Brinjal (Solanum melongena Linn.) is one of the widely used vegetable crops and is popular in many countries viz. Central, South and South-East Asia, some part of Africa and Central America (Gurubban, 1977). It is also known as the aubergine, eggplant, melongene, guinea squash etc. Various data indicate that from the several species that evolved in Africa, one (Solanum incanum), gave rise to a distinct species which spread to South-East Asia as the wild ancestor of Solanum melongena (Lester, 1998). It was domesticated in India from the species Solanum incanum and India or Indo-China region is recognized as the centre of the eggplant diversity (Vavilov, 1951). Solanum melongena is a delicate, tropical perennial often cultivated as an annual in temperate climates. The fruit is botanically classified as a berry and contains numerous small, soft seeds which are edible, but have a bitter taste because they contain nicotinoid alkaloids. This is unsurprising as it is a close relative of tobacco.

‘Cucurbits’ is a term coined by Liberty Hyde Bailey for cultivated species of the family Cucurbitacae (Robinson and Decker-Walters, 2004). Presently, the term has been used not only for cultivated forms, but also for any species of the family Cucurbitacae. Among vegetables, the cucurbits form one of the largest groups with their wide adaptation from arid climates to the humid tropics. The family consists of about 118 genera and 825 species. In Asia, about 23 edible major and minor cucurbits are grown as vegetable. They are grown in summer and rainy seasons in India and even in winter in some parts of southern and western India as both annual and perennial crops. 

Potato is one of the major non cereal food crops in the world and ranks fourth after rice, wheat and maize. Due to its high production potential per unit area and time, the crop has been recorded for sustaining millions of lives during the times of war and hunger. Native of South America, this crop was introduced into India in early seventieth century. Currently India ranks 3rd for area and 2nd for production in the world [AICRP (Potato) Bulletin No. 2]. Potato is generally grown as rabi crop during October to December in gangetic plains of India but in hills it is grown almost throughout the year as commercial cultivation. In some states like Karnataka, it is generally grown during kharif season.

Okra (Abelmoschus esculentus Moench), otherwise known as Lady’s finger or Bhindi is an annual malvaceous plant and the sixth important vegetable crop cultivated throughout the country mostly in kharif and summer seasons. Though it is reported to be originated from tropical and sub-tropical Africa, but it has gained much importance in India as the secondary centre of origin. India ranked first in okra production in the World and major okra producing Indian states are Uttar Pradesh, Bihar, Orissa, West Bengal, Andhra Pradesh, Karnataka and Assam (Anonymous, 2011).

Tomato, Lycopersicon esculentum Mill. is an important vegetable cultivated throughout the world; both outdoors and under protected structures for fresh market consumption and processing. In India this nutritive rich vegetable is grown over an area of 0.60 m ha with an estimated production of 11.9 mt. Productivity of tomato in India is lower (18.6 t/ha) than the world productivity (27 t/ha) (Anonymous 2009). Tomato is grown in a wide range of climatic conditions across states of Andhra Pradesh, Orissa, Karnataka, Maharashtra, West Bengal, Bihar, Gujarat, Uttar Pradesh and Chhattisgarh. Tomato crop is highly sensitive to environmental stress caused by high temperature and low soil moisture. In fact, temperature is rising in the tomato growing locations and can cause reduced fruit set and lower the quality of fruits.

Members of the family Cruciferae commonly used as vegetable include Cabbage, Cauliflower, Broccoli, Brussels sprouts and mustard etc. The genus Brassica is known for its important agricultural and horticultural crops. A dislike for cabbage or broccoli can result from the fact that these plants contain a compound similar to phenylthiocarbamide (PTC), which is bitter or tasteless to some people depending on their ‘taste buds’ (Theresa, 1995). Almost all parts of some species or other have been developed for food, including the root (turnips), stems (kohlrabi), leaves (cabbage), flowers (cauliflower, broccoli), buds (Brussels sprouts, cabbage), and seeds (many, including mustard seed, and oil-producing rapeseed). Some forms with white or purple foliage or flowerheads are also sometimes grown for ornamental purpose.

The green pepper or chilli is reported to be the native of tropical America (Thompson and Kelly, 1957). This was widely cultivated in Central and South America in early times and was unknown in Europe prior to the discovery of America. The chilli belongs to the family Solanaceae and genus Capsicum. Only four species are under cultivation, out of which the cultivation of the two, Capsicum pendulum and Capsicum pubescens, are restricted to South and Central America. The other two, Capsicum annuum and Capsicum fruitescens are commercially cultivated throughout the world. Capsicum annuum is the most commonly cultivated species and all green chillies in the market and most dry chillies belong to this group. Most of the small and highly pungent chillies belong to Capsicum fruitescens.

In countries like India where majority of the population are vegetarians, leguminous vegetables serve as the major source of protein in the diet. In the developing third world countries, especially for the poor, the major protein source in the diet are vegetable legumes. Most leguminous vegetables are rich in phosphorus, calcium, iron and a number of essential vitamins. Crops like soybean, groundnut and Bamabara groundnut are also rich in fats which are needed by the body to absorb vitamin A.

Sweet potato, Ipomoea batatas (Linn.) originated in northwestern South America around 8000 - 6000 BC. The plant is a dicotyledonous, herbaceous, trailing vine which is the only economically important member of the family Convolvulaceae. The plant is generally characterised by starchy, succulent and tuberous storage roots; alternating palmately lobed leaves and medium sized sympetalous flowers which grow individually and vary in colour from white to varying degrees of purple (Austin et al., 1991). It is a perennial plant but is grown as an annual by vegetative propagation usually through vine cuttings and sometimes using either storage roots. Its growth habit is predominantly prostrate with a vine system that rapidly expands horizontally on the ground. The types of growth habit of sweet potatoes are erect, semi-erect, spreading and very spreading.

Moringa oleifera Linn. belongs to the family Moringaceae, that consists of only one genus with about 13 species of deciduous trees (Keay, 1989). It is believed to be the native of India-Pakistan-Nepal borders, but now is becoming widely distributed and grown in several countries, particularly in tropical and subtropical regions (Satti et al., 2013). Besides some other species, M. oleifera is recently being the most widely cultivated in numerous countries in Asia, including the Arabian Peninsula, central and south America and in most African countries like Benin, Burkina Faso, Cameron, Senegal, Mauritania, Niger, Nigeria, Tanzania, Uganda, Kenya and Sudan (Nasir and Ali, 1972; Ramachandran et al., 1980 and Parrotta, 2001).

Curry leaf, Murraya koenigii (Linn.) is one of the most important plants exclusively known for its culinary and medicinal value. Leaves of the plant are widely used for flavouring food in Indian cookery. Leaves are also used in many Indian Ayurvedic and Unani prescriptions (Joseph and Peter, 1985). The whole plant including leaves, stems, flower, fruits and roots are used as tonic, stimulant, anti-flatulent, anti-diabetic, anti-oxidant (Khan et al., 1997) and anti-carcinogenic (Khanum et al., 2000). The plant is also used in curing digestive disorder, kidney disorder, burns and bruises, improving animal fertility, increasing shelf life of meat products, prevention of premature graying of hair and strengthening gums and teeths (Tara and Sharma, 2010). The plant is most widespread all over India and in some places it is grown wild. 

Coriander, Coriandrum sativum L. is an erect annual herb belongs to the family Apiaceae. Coriander may also be referred to as Cilantro, Chinese parsley or Dhania. In India it is cultivated in Rajasthan, Gujarat, Madhya Pradesh, Tamil Nadu, West Bengal, Uttar Praesh etc. The leaves of the plant are variable in shape, broadly lobed at the base of the plant. Leaves are slender and feathery higher on the flowering stems. It is a soft, hairless annual plant, surviving only one growing season. Except root all parts of the coriander plant are edible, but the fresh leaves and the dried seeds are most commonly used. It is also used as a condiment for its medicinal properties. Green leaves of coriander are extensively used for culinary purposes for a sweet aroma in cooking.

Leafy vegetables are the herbs that are grown for their edible greens (leaves). Leafy vegetables are also called pot-herbs, greens, vegetable greens, and leafy greens are plant leaves eaten as a vegetable, sometimes accompanied by tender petioles and shoots. They come from a very wide variety of plants. As per Singh and Arora (1978), about 220 species belonging to the families, Amaranthaceae, Chenopodiaceae, Araceae, Asteraceae, Convolvulaceae, Malvaceae, Nymphalaceae, Papilionaceae etc. occur in India. Although most of them are grown wild, a few are regularly cultivated and consumed as cooked vegetables.

Elephant foot yam, Amorphophallus campanutatus Blume (= Arum campanulatum Roxb.) belongs to the family Araceae. It is also known as elephant yam, Elephant bread, Suran, Sweet yam etc. It is a native to Tropical Asia and is found throughout the plains of the Indian sub-continent and some other parts of South East Asia and Africa growing both wild as well as cultivated. It is a robust herbaceous plant, with an erect solitary stem usually 1-2.5 m in height and bearing at the top one or two tripartite leaves, each part of which is deeply dissected into numerous segments. Towards the end of the plant’s cycle (usually 4-6 years) a large terminal inflorescence is produced, consisting of a short stalk and spathe and a spadix, which emits a malodorous smell, reminiscent of rotten meat.

Protected cultivation practices can be defined as a cropping technique wherein the micro environment surrounding the plant body is controlled partially or fully as per plant need during their period of growth to maximize the yield and resource saving. Cultivation of vegetables under protective structures such as net houses has become popular in recent years (Kaur et al., 2004; Cheema et al., 2004; Singh et al., 2004). This enables, farmers to produce vegetables in the off-season, when fresh produce usually fetches higher price in the market.

Endowed with varied agro-climatic situations, topography and soil type, India has been a leading vegetable producing country in the world occupying the second position in vegetable production after China with an annual production of 87.53 million tonnes from 5.86 million hectares having a share of 14.4 per cent to the world production. With commercial cultivation of as many as 61 annual and 4 perennial vegetables, India is the most diverse vegetable growing country in the world (Prakash et al., 2006). It is quite encouraging to know that our country occupies first position in cauliflower production and second in onion production. In India vegetables are grown both as mono-cropping (vegetable-vegetable cropping system) and sequential cropping after cereals, oil seeds and pulses. Besides, intercropping of vegetables with upland rice, maize, sugarcane, mango, papaya, banana and other fruit crops are also being encouraged in many areas. Vegetable based farming is rapidly emerging as one of the important  production systems in India  as this enterprise produces  a much higher income than any other type of farming in a shorter period of time. 

Vegetables are the largest important constituent of our daily diet as well as high value cash crops for small, marginal and large scale growers. These are rich in proteins, vitamins, minerals and dietary fibre which are essential for our normal body functions, prevention of malnutrition and deficiency diseases. Vegetables also play key role in neutralizing the acids produced during digestion of fatty foods and also provide valuable roughages which help in movement of food in intestine. Some of the vegetables are good sources of carbohydrates (leguminous vegetables, sweet potato, potato, onion, garlic and fenugreek) proteins (peas, beans, leafy vegetables and garlic) vitamin A (carrot, tomato, drumstick, leafy vegetables), Vitamin B (peas, garlic and tomato), vitamin C (green chillies, drumstick leaves, cole crops, leafy vegetables and leaves of radish) and minerals (leafy vegetables, drumstick pods etc.). As per dietician recommendation, our daily requirement is 75-125g of green leafy vegetables, 85g of other vegetables and 85 g of roots and tubers with other food (http://AgriInfo.in).

Mites are small arthropods belonging to the subclass Acari (also known as Acarina) and the class Arachnida. The scientific discipline devoted to the study of ticks and mites is called acarology. In soil ecosystems, mites are favored by high organic matter content and by moist conditions, wherein they actively engage in the fragmentation and mixing of organic matter (Nyle and Ray, 2009). Mites are among the most diverse and successful of all the invertebrate groups. They have exploited an incredible array of habitats, and because of their small size (most are microscopic), go largely unnoticed. Many live freely in the soil or water, but there are also a large number of species that live as parasites on plants, animals, and some that feed on mold. It is estimated that 48,200 species of mites have been described (Halliday et al., 2000).

Biological control is a strategy which employs utilization of natural enemies to reduce the damage caused by noxious organisms to tolerable levels (De Bach and Rosen, 1991). This is the most benign method for reducing pest population in vegetable ecosystem. It opens an amicable platform for production of organic vegetables with good export value. Since the late 1950s, much of the insect control in vegetables has been based on the use of synthetic chemical insecticides. Insecticides are relatively easy to use and have generally provided effective pest control. It is likely that they will always be a component of pest management programs. But, insecticides have some undesirable attributes. They usually present some degree of hazard to the applicator and other people who may come in contact with them, they can leave residues that some find unacceptable; they can contaminate soil and water and affect wildlife, aquatic life and other non-target organisms, they can interfere with beneficial organisms, such as pollinating insects and the natural enemies of pests. The insects also can develop resistance to insecticide. For these reasons, there is growing interest among farmers, entomologists and gardeners to explore and adopt methods that reduce pesticide use.