eChapters

Introduction Feed is a major source of nutrition in semi-intensive and intensive culture systems. Fish fed with formulated feed is used for their growth, maintenance, and reproduction. Feed Energy utilized for maintenance is mainly for health and survivability. In intensive aquaculture, animals almost exclusively depend on an external supply of high protein feed (generally >20%), usually based on fishmeal (Beveridge and Little, 2002) because of its high protein content, better bioavailability of amino acids, palatability, and unknown growth factors. Hence fish fed with a fish meal-based diet exhibits better growth performance, feed conversion, and fish health than fish fed with other animal and plant-based protein sources (Hardy and Tacon, 2002; Pike and Barlow, 2002; Tacon, 2003; Cook et al., 1996). Still, Global fish meal production is annually decreasing since 1994 due to increased human utilization and increased use of fish residues and by-products, increasingly replacing whole fish for fish meal (FAO, 2020). Hence many scientists were passionate about replacing the fish meal with an alternative feed ingredient without compromising growth.

Introduction “Xenobiotics” are “foreign compounds,” which are alien to the organism and removed from their natural environment. Xenobiotics are substances that are either alien to an organism or do not form a natural part of its diet. Compounds including pharmaceuticals, food additives, & environmental toxins are examples of xenobiotics. Normally, these substances are removed from the body by being broken down into compounds and then being expelled through the kidney, bile and lungs. For the pharmaceutical business, enzymes that metabolize xenobiotics are crucial because they are in charge of breaking down medicines. Similarly, xenobiotic transporters influence how long medications remain in the body.

Nanomaterials are a rapidly growing technological sector with diverse applications. These nanomaterials are categorized into distinct groups according to their shape, size, and materials used in their fabrication. The synthesis of nanomaterials follows different strategies that are tailored to their specific applications. This chapter describes the different approaches used for the synthesis of nanomaterials, including top-down, bottom-up, and hybrid approaches. Furthermore, this chapter discusses the advantages and disadvantages of each fabrication method and explores the diverse applications of nanomaterials across multiple fields.

Surface-Enhanced Raman Spectroscopy (SERS) may detect and identify chemical and biological species ultrasensitively. Through localized surface plasmon resonance (LSPR) effects, metal nanostructures boost analyte Raman signals. This chapter covers current advances and essential principles in metal nanostructures for SERS chemical detection. It discusses SERS fundamentals and enhancing processes, such as metal nanostructure size, shape, and composition. Top-down and bottom-up processes including lithography, chemical synthesis, and self-assembly are used to create repeatable and controllable metal nanostructures. The complex interactions between light, metal nanostructures, and analyte molecules are best understood by combining theoretical modeling and experimental observations. 

Nanomaterials have emerged as promising candidates for revolutionizing sensing and detection technologies, offering unprecedented capabilities in sensitivity, selectivity, and miniaturization. The current chapter provides a concise overview of recent advancements in the utilization of nanomaterials for sensing and detection applications. It encompasses a diverse range of nanomaterials, including nanoparticles, nanotubes, and nanowires, each exhibiting unique properties that enable enhanced performance in sensing applications. The integration of nanomaterials into sensing platforms has demonstrated remarkable progress in various fields, such as environmental monitoring, healthcare diagnostics & security applications.

This section explores how nanoparticles have a significant influence on sensing and detection, explaining how they have revolutionized analytical capabilities. Our trip through many kinds of nanomaterials, such as metal nanoparticles, semiconductor nanomaterials, and carbon-based structures, aims to explore their distinct features and how they might be used for novel sensing methods. The intricacies behind sophisticated sensor technologies are clarified through an examination of plasmonic sensing, quantum dot applications, and conductive nanomaterial responses. In order to improve selectivity, the chapter emphasises surface modifications and biomimetic coatings as key components of strategic functionalization techniques.

Nanomaterials, a cornerstone of nanotechnology, encompass a broad array of particles showcasing remarkable properties and diverse applications. This chapter outlines the classifications and applications of various nanomaterials, including organic, semiconductor, metal, metal oxide, and carbon-based nanoparticles. Each type offers unique characteristics, such as biodegradability, optical and electrical properties, making them valuable in fields like drug delivery, electronics, and catalysis. Furthermore, this study focuses on the interactions of nanoparticles with living organisms, emphasizing their impact on immune systems across plants, invertebrates, and humans. 

Synthesis of nanoparticulate metal composites (NMCP) presents a multitude of advantages compared to conventional dosage forms. Acne, a multifactorial skin condition, predominantly involves the pilosebaceous unit and is primarily caused by bacterial species such as Propionibacterium acnes and Acne vulgaris. A staggering 95% of the global population is afflicted by acne. Leveragitng NMCP strategies holds immense promise for innovating novel, efficacious, and low-dose treatments for managing acne. This review delves into various nanotechnological methodologies tailored for effectively addressing acne. Methods: This review encompasses recent advancements pertaining to NMCP carriers aimed at treating acne.

Nanomedicine, an interdisciplinary field at the intersection of nanotechnology and medicine, has emerged as a promising avenue for addressing complex health challenges. One area of significant interest is the application of nanotechnology in maintaining and improving gut health. This chapter provides a concise overview of the current state of research in nanomedicine's role in promoting gastrointestinal well-being.

Nanoparticles, with their unique physicochemical properties, offer novel approaches for targeted drug delivery, imaging, and diagnostics in the gastrointestinal tract. Engineered nanoparticles can navigate the harsh conditions of the digestive system, delivering therapeutic agents precisely to the intended sites within the gut.

Despite substantial advances in the diagnostics and treatment of diseases, parasitic infections are a major global health issue causing significant mortality and morbidity. Currently, chemotherapeutic antiprotozoal drugs, anthelmintic and anti-ectoparasitic agents are used to treat, but resistance to these drugs has developed due to overuse. In this scenario, nanoparticles are proving a major breakthrough in the treatment and control of parasitic diseases. In the last decade, there has been enormous development in the field of nano medicine for parasitic control. Gold and silver nanoparticles have shown promising results in the treatments of various types ofparasitic infections. These nanoparticles are synthesized through the use of various conventional and molecular technologies and have shown great efficacy. 

The main objective of nanomedicine broadly defined as the comprehensive monitoring, repairing and improvement of all human biological systems, working from the molecular level using engineered devices and nanostructures to achieve medical benefit. Nanomedicine is the nanomachine of diagnosing, treating, and preventing disease and traumatic injury, relieving pain, and of preserving and improving human health, using molecular tools and molecular knowledge of the human body. Nanotechnology applications in medical science can be essential in achieving this goal. These applications involves extensive surveillance, control, creation, repair, and defence of all biological human systems, employing designed nanodevices and nanostructures which works in molecular level.

Nanotechnology has been successfully applied in various fields such as agriculture, biochemistry and medicine. However, its application in food systems has been new and is yet to be scrutinised. It offers a range of physical and chemical benefits that can be employed in production, development, fabrication, packaging, storage and food distribution systems. These novel nanomaterials such as nanocapsules, nanocomposites, nanoemulsions, nanoencapsulation, nano packaging, nanotubes and nanosensors have been used to improve food quality with better shelf life. However, there is concern about the safety of these nanomaterials, especially because of partial knowledge about the effects of these materials on human health.

Nanotechnology has emerged as a revolutionary force in the food industry, providing innovative solutions to improve food quality, safety, and usefulness. Researchers have devised novel ways to numerous issues in food production and preservation by harnessing nanoparticles' unique traits, such as their high surface area-to-volume ratio and customizable physicochemical characteristics. Nanotechnology-enabled food additives provide a wide range of benefits, including improved texture, taste, color, and nutritional value, as well as increased shelf life and microbiological safety. Furthermore, nanoparticles are effective transporters for bioactive chemicals, allowing for targeted and regulated release within the food matrix.

The increase in population and global industrialization has led to environmental pollution, which is a significant threat to the health of the ecological system. Different measures are recommended to remediate polluted areas effectively. The applications of nanotechnology in medicine, cosmetics, sports, textiles, and pharmaceuticals have increased over the years. Another approach to remediate the adverse effects of pollutants on the environment is by utilizing nanotechnology for contaminant remediation. Biogenic nanoparticles are tiny particles produced by biological entities such as fungi, bacteria, yeast, and algae. These biogenic nanoparticles are efficient in removing pollutants like heavy metals, pharmaceutical waste, dyes, and hydrocarbon waste. 

The hazardous toxic metals like cadmium (Cd), arsenic (As), mercury (Hg), lead (Pb), and chromium (Cr), which have detrimental health effects, are naturally discharged into the atmosphere in various ways viz., industrial wastes, anthropogenic sources, etc. Heavy metal pollution of the atmosphere has become a frightening ecological concern that has created serious threats to the ecosystem. These metals have been identified as group I, human carcinogens due to their persistence in the surroundings and bio-magnification in biological systems. Thus, the removal of heavy metals from the atmosphere becomes a serious matter from the biological and environmental point of view. In the past following techniques adoptedfor toxic heavy metals remediation were classified are bioadsorption, ion exchange, membrane filtration, flotation, and solvent extraction techniques.

One ofthe biggest issues the world is facing today is the lack of clean and pure water. Due to rising water demands, rigid health regulations, and xenobiotic pollutants, traditional wastewater treatment technologies cannot provide safe water. The present era necessitates innovative approaches to wastewater treatment technologies and improved water resource conservation and management materials. By utilizing innovative nanomaterial, nanotechnology guarantees a continuous provision of potable water and contributes to the preservation of water sources. Nanomaterials expedite rapid processes for the purification, conservation, and reuse of wastewater, complementing other enduring industrial methods. 

Nanotechnology holds immense promise in bolstering environmental protection and sustainability by revolutionizing approaches to monitoring, addressing, and amending environmental pollutants. This paradigm shift extends to resource conservation and energy efficiency through the innovation of more adept technologies. Yet, as we harness the potential of nanotechnology, it is of prime importance to meticulously evaluate its environmental and health implications, instating stringent measures to mitigate risks. Responsible and sustainable development, coupled with effective regulation, is imperative.

Agriculture serve as a backbone in improving economic growth of a country as well as it provides a base in meeting various needs of people in direct and indirect ways. The recent advancement in nanotechnology has shown a path to develop traditional agriculture into a sustainable practice. Several nanochemicals emerged as promising agents for better plant growth, used as fertilizer, pesticides, control weeds and also used as antimicrobial agents in food packaging. Nanotechnology may act as sensor for checking soil health of agriculture fields.

Over the years synthetic pesticides like herbicides, insecticides nematicides etc. have been used to improve crop yield. Indiscriminate application of pesticides ultimately leads to their excess discharge into water bodies during rainfall and causes death of fish and other aquatic life. Also consumption of seafood/fishes may cause biomagnification of chemicals in human body and leads to several lethal diseases like cancer, diabetes, neurodegenerative disorders like Parkinson, Alzheimer, and amyotrophic lateral sclerosis (ALS), birth defects and reproductive disorders. Likewise synthetic pesticides also damage soil texture, soil microbes and soil fertility. Their residues enter into plants and animal systems and further move into animals or humans body through food chain.

Nanotechnology epitomizes one of the most dynamic and transformative fields in modern science and technology. This multidisciplinary domain bridges chemistry, physics, biology, along with engineering, enabling the creation of materials and devices with extraordinary properties and applications. The book chapter reflects the research and patenting trends in nanotechnology. USA leading the global share for most patents granted followed by South Korea, Japan, China and Germany for the top five spots contributing more than 76% of all the granted patents by EPO & USPTO related to nanotechnology. Nanotechnological products in relation to sub-industrial areas of medicine, food, agriculture, cosmetics, environment, and renewable energies are also highlighted in chapter. 

Soil is a natural resource that exists on the planet much before the existence of mankind on it. The human relationship with soil throughout the history of mankind has marked its ability of crop production and influenced the success of civilisation. Such relationships also affirm soil as the foundation of agriculture and food security, supplying all the essential ingredients to plants, as fundamentals to life on planet, and support various biogeochemical cycles on earth’ s terrestrial ecosystem. Prosperity of human society depends on the utilisation of planet’ s resources in creative and productive ways. Of these resources, soil has gained much importance as it provides human to sustain themselves with their capacity to food production, to make significant contribution towards biodiversity and other ecosystem services that are vital for the functioning and resilience of earth’ s environment. Soil occupies a pivotal position in the environment to maintain its quality.

Soil is a dynamic natural body of the uppermost layer of earth’s crust produced by the transformation of mineral and organic substances on the earth’ s surface under the influence of environmental factors over a long period. It is the most basic of all natural resources upon which all living forms on the terrestrial ecosystem directly and indirectly depends. However, soil resources are finite, nonrenewable, fragile and heterogeneous in space and time. As a component of pedosphere, it occurs as interface between the lithosphere and atmosphere and strongly interacts with biosphere and hydrosphere (Figure 1 & 2).

The organic constituents of soils or soil organic matter is the most essential components of soil consisting of plant and animal residues at various stages of decomposition, cells and tissues of living or nonliving organisms and the substances synthesized by their decomposition. Soil organic matter exerts profound effect on soil productivity as it acts as source and sink of plant nutrients especially nitrogen and sulphur. It also involves in major biochemical processes to transform or release of plant nutrients into their available forms. Thus, it plays vital role in soil fertility maintenance, through increasing cation exchange capacity and improving soil physical properties, such as bulk density, aggregation, water retention capacity and also supports all kinds of biological activities in soil. The soil organic matter mostly concerns only with dead organic fractions formed from the decomposition of original plant and animal residues using as a source of food and energy by the soil microorganisms. It can be distinguished into –

Soil Colloids A colloid, also known as colloidal solution or colloidal system, is a mixture in which finely divided particles (less than 1µm in size) known as dispersed phase are suspended in a medium, called dispersion medium. The particles must be dispersed in a medium and both the dispersed phase and dispersion medium may be solid, liquid or gaseous which leads to numbers of possible colloidal systems. In soil, the clay fraction (< 2µm in size) together with finer fractions of some organic matter forms the composition in a state of colloidal nature, known as soil colloids. The soil solids as dispersed phase predominates in the dispersion medium (soil solution). As such, colloids in a soil are referred to as ‘sol’. Clay colloids display the most reactive fractions of soil governing their distinct properties such as adsorption and exchange of ions, zeta potential, flocculation and other electrokinetic phenomenon.

The major components of soil consisting with mineral and organic matter, water and air produces a three phase systems of solid, liquid and gas. Many of the soil properties influencing crop growth and other uses depend mostly on the relative proportions of these components as well as the size, shape and arrangements of the solid matters. The physical properties of soil have strong significance in sustaining agricultural productivity. Fertiliser alone or in conjunction with suitable crop varieties and plant protection measures cannot be sufficient towards improving crop productivity unless the soil physical properties are maintained at satisfactory level. Improvement and restoration of physical properties in soil are necessary for protection of soil resources against degradation. The physical properties of soil discussed in this chapter includes soil densities, texture, structure, porosity and consistency of soils and colour of the soil.

Water is absolute necessary constituents for the survival and growth of all the living substances on earth. It is the most essential ingredients for many of the physiological and metabolic process in plants, like photosynthesis to form sugars, translocation of cell constituents and maintenance of cell turgidity. Soil, being an adsorbent of water received from precipitation or rainfall acts as reservoir to meet requirement by plant during growing season. Water retained in the soil serves as solvent to dissolve salts and nutrients and as a carrier to translocate them for absorption by plants. It plays significant role in weathering reaction, soil forming processes and profile development. Water is also important for growth and activities of microorganisms influencing decomposition of organic matter, transformation of mineral nutrients and other physical, chemical and biological properties in soil. This chapter deals with the retention and movement of water in soils to obtain better understanding of soil-water-plant-atmosphere relationships.

Temperature is the measure of the thermal state of a body with respect to its ability to transfer heat. Soil derives its heat almost entirely directly from the sun and losses much of it back into the atmosphere. The major processes for heat transfer in soil are: Radiation, Convection, Conduction and Latent heat exchanges between soil and atmosphere. The most important source of which is the incident radiation supplying almost all the heat energy for the biosphere and also determines the thermal regime of soil. Soil temperature or thermal regimes of soil is an extremely important property of soil as it regulates plant growth directly and influences moisture and aeration status in soil, soil structures, microbial activities and decomposition of plant residues and the availability of plant nutrients . It is controlled mainly by its thermal properties and radiation exchange over the surface and their variations within the soil. The quantity of incident solar radiation and heating the soil depends on the several factors such as exposure and latitude, albedo, soil colour, slope vegetation and composition of soil.

The solid phase of a soil system makes up a mixture of inorganic and organic materials. The inorganic fraction of soil originated from the weathering of rocks and minerals consists of rock fragments and minerals of varying sizes and composition. Hence, this inorganic soil fraction composed by soil minerals also referred as mineral fraction of soil and is caused due to alteration of mineralogical composition of soil by bioclimatic factors. A great deal of attention is being paid to the composition of minerals in soils, their formation and distribution over the earth’s surface. Soil genesis or pedogenosis (a more useful term as soil belongs to pedosphere) deals with the processes of formation and development of soil. The branch of soil science that integrates the studies of genesis, morphology and classification of soils as natural body is called Pedology. The process of weathering of rocks, pedogenesis and development of soil profile are described successively in this chapter.

Classification means the process of ordering or grouping of objects having large number of population and wide variations into shorter one in a systematic manner with selected characteristics. Soils being the natural objects have no exception with other objects to classify them in a best possible way. Thus, soil classification refers to the systematic categorization of soils into various groups, classes or any simpler form based on the similar properties and other distinguishing characteristics. The main purposes of soil classification are to organize knowledge, easy remembering of the soil properties for each group and better understanding about the components and the relationships among individuals and various groups of soils. Various soil classification systems have been evolved during the past for categorizing the soils into various groups but the Soil Taxonomy has been now accepted as most scientific system of classification.

Soil survey is essentially a systematic examination of morphological, a set of other variable soil characteristics, description, classification and mapping of soil in an area alongwith a report making an interpretation to predict their potentials for various uses particularly for crop production.

Activities of Soil Survey Soil survey is composed of the following activities –

1. Anticipation of soil variability - The initial activity of soil survey is obtained by classifying the surveyed data according to different land forms and existing land uses either through field traversing, or aerial photo or by satellite images of the concerned area.

2. Characterisation and classification – This is done on the basis of soil profile description supported with soil analytical data.

3. Soil mapping - This is performed by showing the distribution of types of soil or soil mapping units based on already classified soils with their landforms, and land uses or their combinations.

4. Interpretation - It is the process of making prediction about the potentials of soils for various uses like choice of farm practices – agriculture, horticulture, forestry, pastures etc. and their management practices.

Soil acidity is most conveniently measured by pH of soil suspension with water. Pure water undergoes dissociation into hydrogen and hydroxyl ions and are in equilibrium with undissiociated water molecules Thus, H2 O ??? ??? H+ + OH- (1) and in presence of another H2 O molecule, H+ converts to H3 O+ H+ + H2 O ??? ??? H3 O+ (2) Since water is a weak electrolyte and dissociates as per Eqn. 1, the ionic product of water can be written as – KW = aH+ x aOH- = (CH+ x COH– ) x ( fH+ x fOH-) (3) where, a, C, and f represents the activities, concentrations and activity coefficients of respective ions. In pure water and in dilute solutions the activity coefficients are approximately unity thus the product of concentrations of H+ and OH-1 is the ionic product of water and at ordinary temperature (250 C) this has a constant value of 10-14 gm ions per litre so, Kw =(CH+ x COH–1) = 10-14 gm ion per litre (4) such that, CH+ = COH–1 = 107 gm ion per litre Therefore, if hydrogen ion concentration of an aqueous solution exceeds this value, (10-7gm ion per litre), the solution is said to be acidic then there will be a proportionate decrease of OH- concentration to maintain the constant value of ionic product.

Salt affected soils can be defined as the soils containing excess amount soluble salts in their profiles in a proportion that adversely affect to soil properties and ultimately on crop growth. The soluble salts present in these soils are composed primarily with calcium, magnesium and sodium as cationic and chlorides sulfates and carbonates as anionic constituents along with the presence of potassium, nitrate and others as minor quantities. All soils invariably contain some soluble salts, but they cause harmful effects on crop growth only when accumulates in excess amount in soil solution or increase their concentration in exchange complex of the soil. Based on the presence of sodium salts and the predominance of sodium in the exchange complex, salt affected soils are classified into main categories of 1) Saline soils – contain excess soluble sodium in soil solution with little or no sodium content in exchange complex, 2) Alkaline (Sodic) soils – contain appreciable quantity of sodium adsorbed in exchange complex of soil but may or may not contain soluble sodium salts in soil solution. These soils are also divided into following types –

The living organisms in the terrestrial ecosystem have unique characteristics of taking up the substances from atmosphere and soil for the synthesis of their own cellular component or as a source of energy. The supply and absorption of chemical compounds required for the growth and metabolism of the organisms may be defined as nutrition and the compounds required by them are called nutrients. The process by which the nutrients are converted to cellular material is known as the metabolism. Out of 118 chemical elements so far detected in the modern periodic table, 92 elements from hydrogen to uranium are naturally occurring, a large portion (more than sixty) of such have been detected in the plant tissues. But, the elements which take part in the nutritional requirement and metabolic processes of the plant are said to be essential elements, others which do not participate in such processes are considered non-essential.

Nitrogen Content in Indian Soil Because of tropical and subtropical climates Indian soils have very low nitrogen content and in the majority of cultivated soil it varies from 0.02% to 0.13%. Low levels of N in Indian soil is primarily attributed to climate and secondarily to cropping. Climate plays the dominant role in determining the nitrogen content in soil through the effect of soil organic matter content. Generally heavy textured soils have higher N content than loamy or sandy soils. Other factors remaining the same, total N content in soil decreases with the increase in annual temperature at a given humidity level, on the other hand, it increases with increasing humidity level at a given annual temperature. Maximum N content in soil occurs in the surface layer of soils and decreases with depth in soil profile. The variation of distribution of N content in soil with depth is attributed by varying accumulation of organic matter in soil profile.

Micronutrients are those elements essential for green plants but required in very small quantity for their growth and development. There are altogether eight micronutrient elements in soil consisting of iron, manganese, zinc, copper, boron, molybdenum and chlorine with the recent addition of nickel. These together with large number of other elements usually present in plants with small concentrations are formed as trace elements. Another element, cobalt is known to be required for microorganisms concerned mainly with nitrogen fixation in legumes affects indirectly the growth of many higher plants, thus, may be considered to be included in the list of essential micronutrient element. Similarly, Vanadium and sodium although present as beneficiary elements for plant growth may also have the possibilities to be enlisted into this group of elements.

Among the various natural resources upon which all living organisms depend, soil is the unique because of its non-renewable in nature, heterogeneity in space and time and susceptibility to degradation inflicted by biotic as well as abiotic agents. Whereas, escalating population demands, in one way, to bring more land under the plough for providing food, fodder, fuel and fibre, simultaneously, on the other way, these finite natural resources are dwindling by leaps and bound, through overexploitations and mismanagement, the combined effect of which leads to land degradation, a serious global threat and major environmental issues in the present times.

Agroforestry is a new name for a set of old practices. The farmers have been practicing agroforestry since ancient times. The general concept of agroforestry is to integrate trees and agriculture so as to create a more diversified landscape, while providing the producers with new environmental and economic benefits. In other words, agroforestry is a method of farming that allows trees and shrubs to grow along with crops and/or livestock, therefore blending agriculture and forestry in the same production system. In fact, man’s association with forest is much older than with agriculture. First man was a food gatherer and hunter in forests. Then he realized that the seeds of the fruits he collected germinated, grew into plants and bore the fruits again and thus man started to cultivate foods. Man’s desire to live in a community created settled agriculture.

A forest is a large area dominated by trees. Many definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing and ecological function. Although a forest is usually defined by the presence of trees, under many definitions an area completely lacking trees may still be considered a forest if it grew trees in the past, will grow trees in the future, or was legally designated as a forest regardless of vegetation type.According to the Food andAgriculture Organization definition, forests covered 4 billion hectares or approximately 30% of the world’s land area in 2006. Forests are the dominant terrestrial ecosystem of earth, and are distributed around the globe. Forests account for 75% of the  gross primary production  of the earth’s  biosphere, and contain 80% of the earth’s plant biomass.

The words ‘system’, ‘sub-system’ and ‘practice’ are commonly used in agroforestry literature. In a broad sense, a system is defined as a group of associated elements forming a unified whole and working together in a well defined regular relation for a common goal. An agroforestry system refers to a type of agroforestry land-use that extends over a locality to the extent of forming a land utilization type of the locality. Sub-system and practice are lower-order terms in the hierarchy with lesser magnitudes of role, content and complexity. However, these terms are used loosely, and almost synonymously. Classification of agroforestry systems is necessary in order to understand and provide a practical framework for evaluating systems and developing action plans for their improvement. Any classification scheme should satisfy the following criteria (Nair, 2008).

Agroforestry is a land use system that involves two or more plant species at least one of which must be a woody perennial. When perennial woody and herbaceous components are grown together on the same piece of land their performance would largely depend on their ability to share various growth resources in a given environmental situation. Due to difference in growth pattern and resource requirement of the components in agroforestry situation, a close interactive relation is obvious. Thus, careful management practices for the components are required to establish a successful agroforestry system. The characteristics of the trees and crops, and their interactions, can be modified with good management practices in order to take advantage of the positive characteristics and minimize the effects of the negative ones. Effective and efficient agroforestry management may be divided into two groups; tree management and agricultural crop management.

In agroforestry systems the various components like tree, crop and pasture exist in different proportions and orientations. It is difficult to find out which agroforestry system is the best suited for a given land situation. Similarly, it is to be decided which technologies are required for refinement and improvement of the existing agroforestry practices. But without sufficient knowledge of the existing system in a particular land situation, it is very difficult to set the research priorities for modification and development of this system. Diagnosis and Design (D & D) is a systematic and objective methodology developed by International Centre for Research in Agroforestry (ICRAF) to initiate, monitor and evaluate agroforestry programmes. D & D is based on the philosophy that knowledge of the existing situation (diagnosis) is essential to plan and evaluate (design) meaningful and effective programmes in agroforestry research for development. The methodology plays a strategic role in all the phases of the agroforestry research process. D & D in agroforestry is unique and it has been specially developed for the following purposes.

Agroforestry systems are not simply systems where trees and crops or animals give useful products to the farmers, rather systems where trees and crops and/ or animals interact. Interaction literally means influence or mutual or reciprocal action. So component interaction refers to the influence of one component of a system on the performance of other component as well as the system as a whole. In agroforestry systems, trees are grown in close proximity to crops and pasture. Their performance would largely depend on their ability to share various growth resources in a given environmental situation. Various interactions take place between the woody trees and herbaceous plants (crops or pastures) which is referred to as tree-crop interface. These interactions take place through the media of soil and microclimate and may exert favourable or adverse effects on the crop. Study of interaction helps to know how the components of agroforestry utilize and share the resources of the environment, and how the growth and development of any of the components will influence the others. Interaction occurs both above and below the ground and includes a complex set of interactions relating to radiation exchange, the water balance, nutrient budget and cycling, shelter and other microclimatic modifications.

Management approaches to soil, including problems of soil degradation and low soil fertility, have recently undergone major changes. The earlier concept was to concentrate on achieving high levels of production from the more fertile areas, leaving the marginal lands for extensive use only. Steeply sloping and highly drought-prone areas were mostly left without any cultivation as production from these areas was hardly cost effective. Soil constraints were to be overcome by inputs like improved crop varieties, fertilizers, chemical control of pests and diseases, and the use of irrigation. The approach of use of newly developed high yielding crop varieties, improved agronomic management practices, use of chemical fertilizers, efficient water management and timely plant protection measures has been successful in achieving large increases in crop productivity in recent years. On the other hand, continuous application of fertilizers at higher rates leads to environmental problems. Yield responses to fertilizers have declined because of soil physical degradation and micronutrient deficiencies.

Farmers have been growing trees for different purposes for thousands of years. Tree species that are grown to provide more than one significant function are called multipurpose trees. These functions may be productive such as producing fuelwood, timber, fibre, fodder, food, medicine, etc. and/or protective such as soil conservation, shade, shelterbelt, microclimate amelioration, land sustainability, biodiversity preservation, etc. All trees are multipurpose; some, however, are more multipurpose than others. Tree species can be multipurpose in two ways. 1. A single tree can provide more than one function. For example, Gliricidia sepium is grown as living fences that provide fuel, fodder and green manure for agricultural crops - all at the same time. 2. Trees of the same species, when managed differently, can provide different functions. For example, Leucaena leucocephala is managed so that some trees will mainly yield wood while others mainly produce leaf fodder.

Trees have been used in cropping systems since the beginning of agriculture. Throughout the world, at one period or another in its history, it has been the practice to cultivate tree species and agricultural crops in intimate combination. In the tropics, human beings underwent a transition from hunting/gathering to the use of domesticated plants and livestock. As a part of the process, they cut down trees, cleared the debris by burning and sowed crops in the ashenriched soil. It was the ‘slash-and-burn’ agriculture, a primary forerunner of the present-day agroforestry and a practice that might have originated in the Neolithic period, around 7000 BC. There are innumerable examples of traditional land-use practices involving combined production of trees and agricultural species on the same piece of land in many parts of the world. Trees were an integral part of these farming systems and they were deliberately retained on farmlands to support agriculture. These practices are now known as agroforestry. However, the ultimate objective of these practices was not tree production but food production.

Multipurpose trees and shrubs are defined as all woody perennials that are purposefully grown to provide more than one significant contribution to the production and/or service functions of a land-use system that they occupy. In agroforestry systems, different species of trees and shrubs can be planted with many types of crops in a variety of patterns. Thus, it is required to know about the methods of propagation and nursery raising, planting and other silvicultural management practices along with the diverse uses of multipurpose trees and shrubs of tropical and subtropical areas before their selection for forestry and agroforestry activities. It is important to select the most suitable tree species since it is not easy to replace them once they have been planted.

The world’s drylands include hyper-arid, arid, semi-arid and dry sub-humid areas where rainfall is highly scanty and variable. Droughts are common in areas / zones where water is the principal limiting factor for agriculture (https:// www.fao.org/3/t0122e/t0122e03.htm) . Dryland soils are characterized by low levels of moisture, organic matter, and biological activity, consequently such soils are very poor in fertility devoid of plant nutrients. When, these soils suffer further degradation in fertility, resulting in erosion, desertification, and salinization when crops are grown on such soils inappropriately without any scientific basis. However, the major factor limiting agricultural production on drylands is the lack of adequate moisture for crop growth or drought.

Moisture deficit causing shortfalls in crop production is the characteristic feature of dryland agriculture. Other adverse factors viz., decline in soil fertility together with play of biotic stresses add to the complexities of dryland crop production. Added to the proven agronomic management to combat the problem of drought in dryland agriculture, there is the need to tailoring of suitable crop varieties which can yield reasonably well under conditions of moisture deficit (Varshney et al., 2021). In this context, the appropriate developmental rhythm along with the combination of the constellation of characters of the crop plant matching with the rainfall and the soil moisture availability patterns of the zone are the important considerations together with stability of yield (Hanson and Nelsen, 1980). This task being a complex one, the problem should be approached through multidisciplinary strategy that should buffer the genetic and breeding efforts.

Soil and water are the basic resources in drylands. Soil supports plant life by providing a medium for their growth and development. It is a non-renewable natural resource and susceptible to rapid degradation through various forms of erosion processes. Worldwide, around 52% of total productive land has been degraded by various kinds of degradation processes and almost 80% of the terrestrial land is affected by water erosion .Further, annually ~10 million hectares (Mha) of cropland becomes an unproductive at the global level due to soil erosion with an average rate of 30 t ha−1 year−1 soil erosion .In India, out of 328 million hectares of geographical area, 68 million hectares are critically degraded while 107 million hectares are severely eroded. Soil degradation in India is estimated to be occurring on 147 million hectares (Mha) of land, including 94 Mha from water erosion, 16 Mha from acidification, 14 Mha from flooding, 9 Mha from wind erosion, 6 Mha from salinity, and 7 Mha from a combination of factors (Battacharya et al., 2015).

Rainfed farming has a distinct place in the Indian agriculture, occupying 67 % of cultivated area contributing 44 % of food grains to our national food basket, supporting 40% of human and 65% of livestock population. The system is characterized by resource poor farmers, poor infrastructure and low investment in technology inputs. Even when full irrigation potential of the country is realized, 50% of the net sown area is continued to be rainfed. The important problems encountered in rainfed areas are unfavorable weather, limited choice of crops and varieties, low cropping intensity and unstable productivity. The research work done by the net work of AICRPDA (All India Co-ordinate Research Project for Dryland areas) centres and SAUs (State Agricultutal Universities) indicated that the production in rainfed environment could be enhanced by 200 % compared to the productivity of farmers’ field by adopting improved cropping systems and agro techniques.