eChapters

Phosphorus is essential for plant growth and is involved in important physiological processes, but its availability in soil is strongly influenced by soil chemical conditions. This chapter provides a systematic treatment of phosphorus management in irrigated soils. It begins with the functions of phosphorus and the classification of soil phosphorus into organic and inorganic forms. The behaviour of phosphorus in alkali soils is discussed along with phosphate fixation, which can substantially influence phosphorus availability to crops. The chapter examines the sources of soil phosphorus used by plants and the major types of phosphatic fertilizers used in agricultural production. Available and total phosphorus are distinguished, providing a basis for assessing soil phosphorus status. The behaviour of phosphate fertilizers after application is considered in relation to their efficiency and crop uptake. The residual value of phosphatic fertilizers is also discussed, highlighting the continuing contribution of applied phosphorus to subsequent crops. Overall, the chapter emphasizes efficient phosphorus management to improve nutrient availability, fertilizer-use efficiency and sustainable crop production in irrigated soils.

Potassium is an important plant nutrient that influences water relations, carbohydrate and nitrogen metabolism, crop quality and resistance to environmental stresses. This chapter examines potassium behaviour and management in irrigated soils. It begins with the functions of potassium and explains the different forms in which potassium occurs in soil, including relatively unavailable, slowly available and readily available forms. Potassium fixation and release are discussed in relation to soil colloids, temperature, drying, soil pH and aeration. These processes determine the amount of potassium available for plant uptake and are particularly important in intensively cultivated irrigated soils. The chapter also considers luxury consumption and interactions between potassium and other elements. Potassium management is discussed through appropriate rates and methods of application and selection of suitable potassic fertilizers. The effects of potassium nutrition on plant behaviour, water utilization, carbohydrate and nitrogen metabolism, crop quality, disease resistance and low-temperature injury are highlighted. The chapter therefore provides a framework for maintaining potassium availability and preventing nutrient depletion in productive irrigated

Secondary nutrients are essential for balanced plant nutrition and sustained soil fertility in intensively cultivated irrigated systems. This chapter focuses on calcium, magnesium and sulphur, examining their sources, behaviour, availability and management in soil. Calcium is discussed in relation to its sources, fate in soil, crop removal, leaching and factors affecting its availability, including high sodium content, parent material and interactions with other cations. Calcium fertilizers and their practical importance are also considered. The chapter then examines magnesium, including its sources, behaviour in soil, uptake by crops, leaching and fertilizer management. Sulphur receives detailed attention through discussion of organic and inorganic forms, elemental sulphur and sulfides, sulphate behaviour and the different forms occurring in rice soils. Processes such as adsorption, leaching and immobilization influence sulphur availability and are therefore important under irrigated conditions. Practical aspects of sulphur management, sulphur-containing fertilizers and crop responses to sulphur fertilization are discussed, including effects on the nutritional quality of forages

Micronutrients are required in small quantities but are essential for normal plant growth and crop productivity. Their availability in irrigated soils can vary considerably because of changes in soil pH, moisture conditions, organic matter, texture and interactions with other nutrients. This chapter introduces the concepts of micronutrient deficiency and toxicity and discusses critical limits used for evaluating micronutrient status. Particular emphasis is placed on boron and zinc. Boron content, deficiency in Indian soils, availability and leaching are examined, together with the influence of soil texture, pH and moisture. Boron indicator plants, correction of deficiency, sources, crop response and frequency of application are also discussed. Interactions between boron and other nutrients receive attention. The chapter then considers zinc content and zinc deficiency in soils and examines the influence of pH, phosphate level, organic matter and adsorption by clay minerals on zinc availability. Methods, timing and rates of zinc application and crop responses are presented to support effective micronutrient management.

Successful irrigation development requires careful evaluation of soil and land characteristics before irrigation is introduced or expanded. This chapter deals with the principles and criteria used to evaluate land for irrigation and determine its suitability for sustained agricultural production. Important soil and land characteristics considered include surface-soil texture, particle-size class of the subsoil, coarse fragments, soil depth, permeability, salinity, exchangeable sodium percentage, slope and drainage. These factors determine the ability of land to store and transmit water, support root growth and withstand potential problems associated with irrigation. The chapter introduces land irrigability classification and explains the overall capability index (Ci), including its calculation and interpretation. Subclasses are considered to identify specific limitations affecting irrigated agriculture. The chapter further discusses land suitability classification and the structure used for assessing suitability. Physical condition of soil is included as an important component of land evaluation. By integrating soil, water and landscape characteristics, the chapter provides a systematic basis for identifying suitable land, recognizing limitations and planning sustainable irrigation development.

The quality of irrigation water has a direct influence on soil properties, crop growth and the long-term sustainability of irrigated agriculture. Water containing excessive salts or undesirable proportions of specific ions can create salinity, sodicity and other soil-related problems. This chapter presents the major criteria used for evaluating irrigation water quality. Salinity hazard is considered as an important indicator of the potential for salt accumulation in the soil and consequent restrictions on plant water uptake. Sodium hazard is examined because excessive sodium can adversely affect soil structure and permeability. The chapter also considers the salt index as a measure relevant to the evaluation of irrigation water. Bicarbonate hazard is discussed in relation to the chemical behaviour of irrigation water and its potential effects on soil conditions. Magnesium hazard is another important consideration in assessing the suitability of water for irrigation. By bringing these criteria together, the chapter provides a framework for evaluating irrigation water before application. Proper assessment of water quality is essential for selecting appropriate management practices and preventing long-term degradation of irrigated soils.

Increasing pressure on freshwater resources has created interest in the use of saline water for agricultural production, particularly where high-quality irrigation water is limited. This chapter examines the management possibilities associated with using saline water while addressing the risks of salinity to soil and crops. It focuses on the role of selected nutrients and soil amendments in improving crop performance under saline conditions. The roles of potassium and phosphorus are discussed in relation to plant nutrition and tolerance to salinity. Zinc is also considered for its importance in maintaining plant nutritional balance under saline conditions. The chapter further examines gypsum as an amendment and its role in managing saline soil conditions. Organic matter is discussed for its contribution to soil physical, chemical and biological properties, while biofertilizers are considered as a component of management under saline environments. The integrated use of nutrients, amendments, organic materials and biological inputs provides approaches for improving the productivity of saline soils. The chapter therefore links saline-water use with appropriate soil and nutrient management for sustainable crop production

Efficient irrigation water management is essential for achieving high crop productivity while conserving limited water resources and minimizing environmental hazards. This chapter presents the principles and practices required to manage irrigation according to crop demand and soil-water conditions. It begins with how plants obtain water from soil and explains irrigation requirements, crop water requirement terminology, water-use efficiency, field water balance and the effective root zone. Crop response to water at different growth stages is considered for important crops including rice, wheat, maize, sugarcane and mustard. Different irrigation methods are described, including surface, corrugation, sub-irrigation, sprinkler and drip irrigation. The chapter provides several approaches to irrigation scheduling based on water-holding capacity, degree of water depletion, soil-water potential, evaporation pans, leaf-water potential, canopy temperature, crop water stress index and leaf reflectance. Methods for measuring irrigation water and flowing water, including water-measuring devices and current meters, are also discussed. Scheduling based on IW/CPE ratio and depletion of available soil moisture provides practical approaches for improving water-use efficiency.

The soil–plant–water relationship integrates the major concepts of soil-water availability, root water uptake and plant transpiration into a unified system. Water movement through the soil and plant is governed by differences in water potential and by resistance within the water-conducting pathway. This chapter examines water uptake by roots and the process of transpiration, emphasizing the continuous movement of water from soil through the plant and ultimately to the atmosphere. Variations in water potential and water flux within the soil–plant system provide the basis for understanding how water is transported under different environmental and soil conditions. The resistance of the water-conducting system is considered as an important factor controlling water movement. The chapter separately discusses water movement through soil and within plants before connecting these processes with water movement from the leaf surface to the atmosphere. Control of transpiration is also examined, linking plant water relations with environmental conditions and crop water use. The chapter provides an integrated framework for understanding soil–plant–water interactions essential for efficient irrigation, crop productivity and sustainable management of water resources.

This chapter introduces the historical development and fundamental concepts of immunology. It highlights the contributions of Edward Jenner, Louis Pasteur, Elie Metchnikoff, Paul Ehrlich, Emil von Behring and other pioneering scientists. Important discoveries related to vaccination, phagocytosis, antibody formation, cellular immunity, ELISA, radioimmunoassay and hybridoma technology are addressed. The chapter also explains antigens, immunogens, epitopes, haptens, adjuvants and the desirable characteristics of an effective immunogen. Questions concerning smallpox and rinderpest eradication, vaccine development and primary and secondary immune responses help readers understand the scientific milestones that established immunology as an essential discipline within veterinary and biomedical sciences.

This chapter examines the major forms and mechanisms of immunity. It distinguishes innate immunity from adaptive immunity and explains specificity, diversity, immunological memory and self–non-self recognition. Natural and artificial forms of active and passive immunity are discussed through examples involving infection, vaccination, maternal antibodies and antiserum administration. The chapter introduces pattern-recognition receptors, pathogen-associated molecular patterns and Toll-like receptors involved in microbial recognition. It also covers inflammation, its cardinal signs, acute-phase proteins and the roles of neutrophils and other innate defence components. These objective questions provide a clear foundation for understanding how animals resist infections and develop long-lasting protective immune responses.

This chapter describes the cells, tissues and organs responsible for immune defence. It examines lymphocytes, macrophages, dendritic cells, neutrophils, mast cells, natural killer cells and plasma cells, emphasizing their respective functions. Primary and secondary lymphoid organs—including bone marrow, thymus, bursa of Fabricius, spleen, lymph nodes and mucosa-associated lymphoid tissue—are discussed. The chapter also covers lymphocyte maturation, antigen presentation, phagocytosis, immune-cell surface markers and the organization of lymph-node regions. Positive and negative selection of T lymphocytes and the formation of memory cells are included. Together, these topics explain how immune components develop, communicate and coordinate effective responses against infectious agents.

This chapter focuses on the structure, classes, properties and biological functions of immunoglobulins. It introduces the basic antibody molecule, including heavy and light chains, variable and constant regions, antigen-binding sites and Fc fragments. The characteristics of IgG, IgM, IgA, IgE and IgD are examined in relation to their distribution and immune functions. Questions cover primary and secondary immune responses, placental transfer, mucosal protection, allergic reactions, complement activation and agglutination. The chapter also addresses antibody affinity, avidity, isotypes, allotypes, idiotypes, class switching and Bence-Jones proteins. It provides essential knowledge of how antibodies recognize antigens and contribute to immune protection and diagnosis.

This chapter explains how B-cell receptors, T-cell receptors and major histocompatibility complex molecules participate in antigen recognition. It differentiates MHC class I and class II pathways and describes the processing of endogenous and exogenous antigens. The roles of dendritic cells, macrophages and B lymphocytes as professional antigen-presenting cells are examined. Topics include MHC restriction, antigenic peptides, proteasomal degradation, ubiquitination and recognition by CD4-positive and CD8-positive T lymphocytes. The chapter also discusses superantigens, opsonization, phagocytosis, T-independent antigens and species-specific MHC systems such as BoLA and the avian B complex. These concepts explain the initiation of adaptive immune responses.

This chapter introduces the complement system as an important component of innate and adaptive immunity. It explains the classical, alternative and lectin pathways of complement activation and identifies the molecules involved in each pathway. The formation and functions of C3 convertase, C5 convertase and the membrane attack complex are discussed. Questions address complement-mediated cell lysis, inflammation, chemotaxis and opsonization. The roles of C3b, C3a, C4a, C5a, properdin, factor H and other regulatory proteins are also examined. By covering the activation and regulation of complement, the chapter explains how this system enhances antibody activity and helps eliminate invading microorganisms

This chapter examines cytokines as essential signalling molecules that regulate immune and inflammatory responses. It introduces interleukins, interferons, chemokines, tumour necrosis factors and colony-stimulating factors. Their sources, target cells and biological actions are considered in relation to immune-cell activation, differentiation, migration and communication. The chapter explains important properties such as pleiotropy, redundancy, synergy and antagonism. It also covers antiviral activity, chemotaxis, inflammation, fever and the regulation of humoral and cell-mediated immunity. Special attention is given to excessive cytokine production, cytokine storms and septic shock. These questions help readers understand how cytokines coordinate protective immunity and contribute to immune-mediated disease.

This chapter explores the four types of hypersensitivity reactions described under the Gell and Coombs classification. Type I immediate hypersensitivity, Type II cytotoxic reactions, Type III immune-complex disease and Type IV delayed hypersensitivity are examined in detail. The roles of IgE, mast cells, basophils, antibodies, complement and T lymphocytes are highlighted. Clinical examples include anaphylaxis, milk allergy, haemolytic disease, transfusion reactions, serum sickness, glomerulonephritis, farmer’s lung and the blue-eye condition associated with canine hepatitis. Diagnostic applications, including the tuberculin and Coombs tests, are also addressed. The chapter explains how exaggerated or inappropriate immune responses can damage tissues and produce disease.

This chapter examines immune-system failure arising from reactions against self-antigens or inadequate immune responses. It introduces immunological tolerance, central and peripheral tolerance, clonal deletion and clonal anergy. Important autoimmune diseases—including myasthenia gravis, Graves’ disease, systemic lupus erythematosus, multiple sclerosis, rheumatoid arthritis and Sjögren’s syndrome—are considered. The chapter also discusses molecular mimicry and the production of autoantibodies. Primary, secondary and severe combined immunodeficiency disorders are differentiated, with examples such as Chédiak–Higashi syndrome. Immune-privileged sites and immunological paralysis are also covered. These topics explain the mechanisms that normally prevent self-reactivity and the consequences that arise when immune regulation becomes defective.

This chapter introduces hybridoma technology and its application in producing monoclonal antibodies. It explains the fusion of antibody-producing B lymphocytes with immortal myeloma cells, selection in HAT medium and the roles of HGPRT and polyethylene glycol. The survival and cloning of hybrid cells and the advantages of monoclonal antibodies are considered. The chapter also discusses tissue and organ transplantation, including autografts, isografts, allografts and xenografts. The immunological mechanisms of acute graft rejection, donor histocompatibility antigens and the involvement of T lymphocytes are addressed. These questions connect laboratory antibody production with transplantation immunology and its diagnostic, therapeutic and research applications.

This chapter deals with the principles and applications of serological tests used to detect antigens and antibodies. It distinguishes primary, secondary and tertiary binding tests and explains antibody titre, affinity, avidity, sensitivity and specificity. Important techniques include precipitation, agglutination, complement fixation, neutralization, immunofluorescence, ELISA, radioimmunoassay, Western blotting and the radioallergosorbent test. The chapter also addresses serum decomplementation and the interpretation of positive and negative reactions. These methods are central to the laboratory diagnosis, surveillance and control of infectious diseases. The objective questions enable readers to compare diagnostic techniques and select appropriate tests according to their principles, applications and analytical performance.