eChapters

Botanical Name: Areca catechu L.
Family : Palmae
Origin : India and South Eastern Countries.
Chromosome no. : 2n=32
Type of fruit : One-seeded berry.
Type of Inflorescence : Spadix 
Useable Part : Kernel or endosperm of the seed. 

The term plantation crops refers to those crops which are cultivated on an extensive scale in contiguous area, owned and managed by an individual or a company. The crops include tea, coffee, rubber, cocoa, coconut, arecanut, oil palm, palmyra and cashew. 
    ·    Coconut, cashew nut, cocoa, arecanut, oil palm and palmyra comes under Ministry of Agriculture.

Abstract

Complex industrial wastewater by using conventional treatment method is a significant challenge for its safe disposal. Recently, two step treatments by aerobic bacteria using activated sludge process followed by rhizofiltration has been recommended as a promising technology for detoxification of complex industrial waste. In activated sludge process recalcitrant compounds are biotransformed along with biodegradation of organic waste. Aerobic treatment may be activated sludge process, trickling filter or aerobic lagoon process, which one is used for treatment  it is based upon the characteristics of wastewater. Carbon and nitrogen ratio along with other organic compound is also play important role for microbial growth and degradation of pollutants. During degradation of various pollutants, metal microbes interaction play significant role for its bioremediation either through adsorption or bioaccumulation.

Abstract

The potent greenhouse gases N₂O and CO₂ are relased by aerobic/anaerobic respiring bacteria, archaea, fungi and protists in increasing amounts from converting virgin rain forest and permafrost soils, over fertilized agricultural fields and grasslands including animal husbandry, compost/waste water treatment plants, oceans, savannahs, forests of the temperate climate zones in annual amounts of 0.5 to 4.2 terragrams (Tg) N₂O-N into the atmosphere after autotrophic and hetreotrophic NH₄⁺ to NO₃- oxidation. With estimated 0.25% industries contribute to the annual atmospheric N₂O-N concentration increase.

Abstract

Understanding the impacts of organic or inorganic nutrient management on soil biology and biochemistry may help to develop more sustainable fertilization strategies. The results from comprehensive study made on a field experiment comparing the long-term (more than 100 years) effects of organic manures and inorganic chemical fertilizers on soil biological and biochemical properties are reviewed. The soils adopted with three nutrient managements viz., no fertilization (control), inorganic chemical fertilizers (IC) and organic amendments (OM) obtained from long-term fertilizer experiment were assessed for physical, chemical, microbiological and biochemical properties in three successive years. The response of most of the assessed soil variables to long-term organic nutrient management was significantly higher than those from inorganic fertilization and control (OM > IC = control).

Abstract

Microbial inoculants are low cost inputs with high benefits in agriculture. Solid carrier based (peat or lignite) inoculants are used in most tropical countries. The carrier based inoculants have short shelf life, are liable to have high contaminants and have shown inconsistent field performance. In recent years, special liquid formulations containing not only the desired microorganisms and their nutrients but also added cell protectants or chemicals that promote formation of resting spores or cysts have been developed. The liquid formulations have longer shelf-life (12 months at room temperature) and are also more tolerant to adverse conditions encountered in storage. Liquid Rhizobium biofertilizers enhanced the soybean crop yields in the United States of America, Brazil, Europe and Asia over carrier based inoculants.

Abstract

Discovery of the agricultural utility of microbes during the later part of the eighteenth century, led to the formulation and utilization of superior microbial strains as biofertilizers, for a wide variety of crops and growing conditions across the world. Though microbial inoculants have been in usage for almost two centuries, they are yet to capture the collective imagination of farmers across the globe, which is essential to meet the larger objective of reducing chemical input usage in cropping systems. One probable reason for this is the existence of large growing tracts that are subject to various abiotic stresses of atmospheric and edaphic origin, which limit the proliferation and efficiency of the microbial strains that are commonly used in inoculant production.  This is obvious, since unlike chemical fertilizers, microbial cells being living systems need to grow and thrive in the introduced eco-systems in order to achieve the desired effects of inoculation. But unfortunately microbial inoculant technology has largely adopted the one size-fit all mindset, which had led to failures of microbial inoculants especially in abiotically stressed growing environments. In such a scenario it would be wise to adopt a location or region specific approach for the selection of superior and locally adapted microbial strains for inoculant production.

Abstract

Soil microorganisms play a major role in the biodissolution of nutrients bound in the soil silicate minerals. Plant nutrients like K, P, Ca, Mg, Fe, Zn, and Mn are bound in them. Silicon is considered as agronomically important as it confers rigidity and strength to crop plants and enhances yield. Biodissolution of these nutrients result in their availability to crops influencing the growth, biomass and yield. The microbial metabolites like organic acids, amino acids, inorganic acids, amines, ammonia, phenolic compounds, extracellular polysaccharides, siderophores, ligands of cations and cation exchange are involved in the biodissolution of K, Zn and Si. Frateuria aurantia, Bacillus mucilaginosus and B. edaphicus and Bacillus sp are recognized as potash mobilizers, silica and zinc solubilizers.

Abstract

Soil is the store house of 1/4^th of the global biodiversity. Arbuscular mycorrhizal (AM) fungi is one of the important group of organism occurring in soil. The beneficial effect of AM fungi in improving plant growth is well documented. Many of the functions performed by AM fungi can provide essential services to human society. These services include nutrient cycling, soil structure, plant growth promotion, resistance against biotic and abiotic stresses and bioregulation of plant development. These services are not only essential to ecosystem function but also a critical resource for the sustainable management of agricultural systems. Recent studies have brought out that both plant biodiversity and ecosystem productivity increases with the increasing number of AM fungi. Thus, it appears that the diversity of AM fungi in soil is a major factor contributing to the maintenance of plant biodiversity and the ecosystem functioning. The role of AM fungi in ecosystem services, plant diversity and land productivity are discussed in this review.

Abstract

Agricultural production is often limited by low phosphorus (P) availability. In developing countries, which have limited access to P fertiliser, there is a need to develop plants that are more efficient at low soil P. Arbuscular mycorrhizal (AM) symbioses are widespread in the plant kingdom and contribute significantly to plant P nutrition and growth in natural ecosystems. Production and application of these beneficial fungi for agricultural purposes has grown over the last decades worldwide. However, the necessity of AM inoculum production via a host plant is still an obstacle to ample utilization of AM fungi in agricultural crops. The present article deals with the basic and applied aspects of AM research and its role in sustainable agriculture.

Abstract

Cyanobacteria comprise a group of photosynthetic prokaryotes, which exhibit versatility in their morphological, biochemical and molecular characteristics and represent an untapped source of novel metabolites and genes. Their structural-functional flexibility makes them successful in diverse and extreme environments including high temperatures or levels of UV light and salinity, and co-exist in symbiotic/parasitic/mutualistic associations with various members of Plant and Animal kingdom. The intracellular colonization of cyanobacteria in wheat and rice roots and their potential as plant growth promoting agents for several crops, besides rice, has led to the deployment of novel formulations of cyanobacteria and agriculturally useful bacteria as biofilms and disease suppressive options in field studies.

Abstract

The nutrition of tobacco plants relies upon the plant genotypic variation and soil characteristics which also influence the various microflora that inhabit the rhizosphere. The investigations were aimed to analyze the role of native and inoculated plant growth promoting bacteria on the uptake of major plant nutrients viz., nitrogen, phosphorus and potassium and also their supportive nature in reducing the infection caused by  Pythium aphanidermatum, the damping-off fungus of tobacco in nursery. Rhizosphere microorganisms include PGPR viz., Azotobacter, Azospirillum, Pseudomonas and Bacillus, AM fungi and Streptomyces. The addition of these microbes as bioinoculants in tobacco integrated nutrient and disease management resulted in better quality tobacco worth premium price.

Abstract
 
This work aimed to evaluate agromicrobes preponderance and activity in maize ecosystem of same soil types (diara land/fragile land) under different agricultural practices. We conducted a five year field survey of grower’s field to investigate the effect of tillage system, maize plant genotypes and soil organic carbon level on preponderance of diazotroph (Azotobacter), plant growth promoting rhizobacteria (Pseudomonas) and arbuscular mycorrhiza (AM) colonization of maize ecosystem. No tillage, traditional maize cultivar and soil organic carbon (>1%) appear to support the preponderance of targeted diazotrophs, plant growth promoting rhizobacteria (PGPR) in maize rhizosphere and AM colonization of maize root. Elevation in the preponderance of bacteria, Azospirillum population in maize root, AM colonization, microbial biomass, nitrogen mineralization, phosphate solubilising microbes, cellulose hydrolyzing microbes and acetylene reducing assay (ARA)  of maize root appeared due to organic fertilization of maize crop.

Abstract

Of the various rhizosphere associated bacteria, Azospirillum species are probably the most studied and appear to have significant potential for commercial application. During the last 35 years of studies of Azospirillum–plant interaction, over 20 proposals were suggested for the mechanism of action by which Azospirillum  enhances plant growth, yield and nutrient uptake. Besides, fixing the nitrogen with associative symbiosis, they impart a number of beneficial effects on plants such as phytohormone production, siderophore production, enzyme production, proliferation of root system, enhanced water and mineral uptake, mobilization of minerals, mitigation of environmental stressors of plants, and moderate biocontrol potential. The following plant responses to Azospirillum inoculation in agriculture crops were often reported: increase the germination percentage and height of the seedlings, increase the total number and length of adventitious roots and root hairs, increase the hydraulic conductivity of the root system, increase in the height of the shoot and dry matter production and yield of the crop plants. The effect of Azospirillum inoculation on the total yield increases of field grown plants generally ranged from 10 to 30 per cent. This article reviews the recent researches on role of Azospirillum in plant growth promotion.

Abstract

Microorganisms execute many key functions that regulate the processes related to the fertility status, nutrient transformation, nutrient conservation, and soil health management that are crucial for agronomic sustainability. Rice soils offer peculiar conditions for microorganisms that support diametrically opposite biochemical reactions under flooded conditions. It is pertinent to note that both reduction and oxidation reactions of several essential nutrients mediated by microbes occur simultaneously in the flooded soils at various depths, profiles and stages of rice crop growth in concurrence. This is peculiar and specific to rice soils as the cultivation process demands changes in water regimes, operative and management practices.

Abstract

Current trend of global agricultural systems entails preference towards sustainable crop production through organic agriculture (ecology based) as compared to conventional (synthetic input based). In order to claim as organic, it needs to be certified as per requirements organic standard. The soil fertility management organic standard requirements of major countries are outlined. This review article compares the agricultural management practices of organic and conventional systems so as to assess its impacts on microbial biodiversity, microbial activities on soil functioning and long term fertility based on long term field studies conducted in different parts of the globe.

Abstract

Any environmental variable, can adversely affect the optimal growth conditions of the plants. The stressed environment makes the plants to alter their physiology for survival rather than reproduction. Prolonged drought, intense raining, frequent floods, cold waves high and low temperatures are the predicted abiotic stresses in the future due to climate changes. Water stress is one of the important growth limiting factor which decreases plant growth during vegetative stage. Crops grown under rain-fed conditions are the most affected by seasonal variations in rainfall. Therefore failure of monsoon, high temperature and salinity usually result in water stress. In addition, it causes serious negative impacts on crop growth and yields. A greater stress tolerance capacity could also be largely attributed to the plants by the symbiotically associating microorganisms capable of modulating stress factors. The microorganisms having close association with plants are referred as plant associated bacteria (PAB), which can be grouped into rhizospheric (in vicinity of root) and rhizoplanic (on surface of root), endophytic (inside the plant tissue)  and phyllospheric (on the leaf surface ) bacteria. Among the PAB, pink pigmented facultative methylotrophic (PPFM) bacteria belonging to the  genus Methylobacterium are well known for their intimate ubiquitous occurrence in the plant.

Abstract

The medicinal plant, Nithyakalyani, Catharanthusroseus is valued for its alkaloid and the content varied, among root (0.14 to 1.43%), stem (0.48%), fruit (0.4%), seed (0.18%) and pericaup (1.14%). The biofertilizer consortium development includes Catharanthusroseus. Azosppirillumlipoferum CAZS-4, Azotobaterchroococcum CAZB-1, Bacillusmegaterium CPB-18 and Pseudomonasflourescens CPF-14. The relative chemotactic response (RCR) of the strains to anionic fraction is more than that of cationic and neutral fractions. The consortium treated plants possessed 1.120 mg g^-1 of ajmalicine on 180 DAS, and the antioxidant superoxide dismutase (SOD) (13.240 U mg of protein hr-1), peroxide (POX) (11.240 U mg of protein hr-1) and catalase (CAT) (9.000 U mg of protein hr^-1) values were higher on 150 DAS. The consortium increased the biomass production by 50-75 per cent with proportionate increase in the mineral nutrient content. Biofertilizer consortium is the most effective organic input for biomass production.

Abstract

Plant-associated microorganisms play a significant role in conferring resistance to abiotic stresses. These organisms include rhizoplane and endophytic bacteria and symbiotic fungi and operate through a variety of mechanisms like triggering osmotic response and induction of novel genes in plants. The development of stress tolerant crop varieties through genetic engineering and plant breeding is essential but a long and strained process, whereas microbial inoculation to alleviate stresses in plants could be a more cost effective environmental friendly option which could be available in a shorter time frame. Considering the current trends available, intensive future research is needed in this area, particularly on field evaluation and application of potential organisms.

Abstract

The pressure due to increase in world population necessitates an increase in agricultural production and this warrants the vital importance of research in plant and soil productivity. Applications of chemical fertilizers and pesticides have resulted in soil pollution, desertification and salinisation which disrupted the agriculture production. A suitable microbial technology to improve the soil health and plant productivity has been invented. Increase in the use of bacterial fertilizers substantially reduced the use of chemical fertilizers. Similarly invention of specific antagonistic microbes which control pathogen and stimulate plant growth resulted in lesser use of agrochemicals. Selection, development and application of such microbial strains to the agronomic crops resulted improving the fertility of such affected soil. The studies on plant growth promoting rhizobacteria (PGPR) on the growth and nutrient uptake of various plants have been well studied. Presently, it has been found that the use of beneficial microbes can enhance the resistance ability to adverse stresses. Some mechanisms by which the beneficial microorganisms are able to stimulate plant growth and arrest plant pathogens include mobilization of nutrients, production of phytohormones, siderophores, organic acids, nitrogen fixation, lowering of ethylene levels in plants and antagonism. Here the recent developments that have been taken place on the interaction between plants and PGPR and their mechanism of action resulting in enhanced agriculture production and soil fertility are discussed.

Abstract

Endophytes are microorganisms  that live inside the living plant tissues for at least part of their life without causing any apparent disease symptoms in the host. In general  they  can be divided into two main types namely, obligate and facultative endophytes. Facultative endophytes are capable to survive in the soil, on the plant surface, inside the plants as well as on artificial nutrients and can be cultured away from their host. Endophytes which inhabit inside plant tissues throughout their lifespan are called as obligate endophytes. Natural products produced by endophytic microbes are found to be antimicrobial, antiviral, anticancer, antioxidants, antidiabetic and immunosuppressant. Therefore, endophytes form an untapped source of novel natural compounds for application in agriculture, medicine and industry.

Introduction

Microorganisms are a great source of genetic diversity, still far from completely known and explored. The intimate association of plants with complex microbial communities is of great importance for the growth and productivity of plants in agriculture. There exists a definite difference in microbial community present in the bulk soil and the neighboring micro environments like phyllosphere, endosphere, rhizosphere and endorhizae. Microorganisms that colonize the plants’ rhizosphere are either pathogenic or beneficial according to their effects on plants and the way they interact with roots. The rhizosphere supports a plethora of microbial populations capable of exerting beneficial, neutral or detrimental effects on plant growth and development. Microorganisms such as bacteria, actinomycetes, protozoa, algae, fungi, and viruses coexist in the rhizosphere; bacteria are the most abundant among them.

Abstract

With the growing awareness on the benefits of organically cultivated food, biofertilization and biocontrol by plant-associated bacteria are being used as alternatives to chemical fertilizers and conventional control methods. It therefore becomes essential to continue surveying different agroecological niches to identify plant growth promoting bacteria suitable for each microenvironment. Species belonging to the genus Enterobacter are versatile colonizers of numerous environmental niches. Several species and strains from this genus have also been routinely recovered from the rhizosphere of crops such as rice, canola, cucumber, banana, potato, corn, tomato and cotton. These isolates have been studied and shown to have beneficial effects on plant growth and protective action against phytopathogens.

Abstract

The greatest challenge facing us in the coming years is to produce adequate amounts of basic necessities of food, feed, fibre, fuel and raw materials for the rapidly shrinking per capita agricultural land. One alternative is to make a sustainable use of existing marginal lands. In many regions of the tropics and sub-tropics, the need to use marginal low-input soils with usually inadequate nutrient(s) supply permits only very low or unreliable yields to be achieved. It is frequently not possible  to supply required amounts of mineral fertilizers or chemical pesticides because of the low purchasing power of the marginal farmers. In particular, it is not possible to compensate for the deficient nutrient supply and this constitutes a yield limiting factor. The role of soil microorganisms in sustainable productivity has been well construed. In recent years, root inhabiting (rhizozosphere) bacteria (rhizobacteria) is gaining importance.

Abstract

The phosphorus deficiency in soil is a major problem for agricultural production as phosphorus is one of the major constituents in energy metabolism and biosynthesis of nucleic acids and cell membranes. The phosphorous present in soil is an important macronutrient for the growth and development of the plants. The phosphorus occurs in two forms in soil, organic and inorganic. The phytates (salts of phytic acid) constitute the major form of organic phosphorus other than nucleic acids, phospholipids and other compounds in soil. Phytate-phosphorus is not readily available to plants due to its chelation with metal ions forming insoluble complexes or adsorbed to soil particles. Phosphate solubilizing and phytate hydrolyzing microorganisms, bacteria and fungi, are ubiquitous in cultivated, wetland, grassland and forest soils, which play an important role in supplying soluble phosphorus to plants. Microbes hydrolyze organic forms of phosphorus by secreting phytases and acidic/alkaline phosphatases. By genetic engineering, several attempts have been made to develop transgenic plants which are able to utilize phytates as sole source of phosphorus for their growth and development. This review focuses on the applicability of microbial phytases in promoting the growth and development of various crop plants.

Abstract

The structure and function of proteins involved in plant-microbe interactions is investigated through large-scale proteomics technology in a complex biological sample. Since the whole genome sequence are now available for several plant species and microbes, proteomics study has became easier, accurate and huge amount of data can be generated during plant-microbe interactions. Proteomics approaches are highly important and relevant in many studies and showed that only genomics approaches is not sufficient as much significant information are lost as the proteins and not the genes coding them are final product which is responsible for the observed phenotype.

Introduction

Biological nitrogen fixation (BNF), generally found in legumes, is a valuable nature’s gift through which atmospheric nitrogen is fixed by symbiotically associated rhizobia that make it available to plants. Among cereals, rice (Oryza sativa) is an important staple food crop that feeds a large proportion of the world population [1]. There is tremendous pressure on agriculturists worldwide to increase the yield to meet growing consumption to feed a world population increasing day by day. However, unlike symbiotic plant–microbe interactions commonly observed in legumes, in several cereal crop plants including Oryza sativa, endophytic associations have been observed [2-8].

Abstract

While, life on Earth is dependent on microbes for many essential services, microbes are intimate partners in virtually every life process of plants by way of mobilization/acquisition of nutrients, out-competition and antagonism of pathogens, plant stress alleviation, plant growth promotion, co-metabolism, degradation of toxins, etc. Exploitation of such interactions between microbes and plants and optimization of plant microbiome could allow farmers to apply less chemical fertilizer, and pesticides besides improving overall plant health which paves the way for sustainable development. What is less appreciated, and less well understood, is the mechanism of microbes exerting such benefits to the plants. A greater understanding of how plants and soil microbes live together, communicate, build innate plant immunity, triggers hormone synthesis and benefit each other can therefore provide new strategies to improve plant productivity, while helping to protect the environment and maintain global biodiversity.

1. Why Plant Nutrient Disorders?

Plant Nutrient Disorders result from nutrient imbalances in soils and plants. In-adequate use of one or more nutrients can result in nutrient imbalances. Presence or use of a nutrient in excess amount can hinder the absorption or uptake of another nutrient and thus,cause nutrient disorders. Lime induced iron chlorosis or use of excess Potassium can hinder the absorption of Ca²⁺/and, or Mg²⁺ by plants. Enhanced level of Mg can decrease the uptake of Zn. Excessive use of NPK fertilisers can result in micronutrient deficiencies.

Soils are being regularly depleted of their native reserves, due to intensive cropping and non-application of essential nutrients (primary, secondary and micronutrients). Lack or restricted use of quality organic manures, such as compost, green manures, crop residues etc. and cultivation of HYVs in most crops have accentuated the problem.

Spatial variability in soil parameters including nutrients has been attributed to the parent material, topography, landforms, cropping pattern, fertilization and manuring practices.. Blanket nutrient recommendations further widen the variability and enhance the risk of soil degradation in terms of soil organic carbon and nutrient mining, acidity, green house gas emission, water and environmental pollution. Unfavorable economics on account of blanket recommendation, adversely influence farmers to increase investments in new crop management technologies. This results in low farm productivity and poor soil health, that jeopardize food security and agricultural sustainability.

Earth provides enough to satisfy every man’s need but not every man’s greed.
—Mahatma Gandhi
The term ‘environment’ is derived from French word ‘environner’, which literary means ‘to surround’ or ‘to encircle’ i.e. everything either living (plants, animals, microbes) or nonliving (soil, water, air, temperature, humidity etc.) surrounding us makes our environment. The universe is full of uncountable number of stars, planet and satellites, which has specific type of environment but earth is the only known planet in the universe that contains life supporting environment. The earth environment is a collective term for the nature or ecosystems, that we use and benefit from on a local, national and global scale. The earth ecosystems provide number of benefits called ecosystem services, free of cost.

In agricultural systems, water quality is usually determined to  assess its suitability for irrigation and/or its use for aquaculture. Analysis of irrigation water is carried out, to know their nutrient load, suitability for irrigation purposes in general and to salt sensitive crops in particular, and their significance as nutrient suppliers as in practical crop production (Tandon,1993). For aquaculture, on the other hand, maintenance of pond environment for survival and growth of aquatic lives, forms the major purpose of such exercises. While both the assessments are mostly governed by some common variables, a few additional attributes are also used for identifying the water quality for these two different purposes. The most important characteristics, that determine the quality of irrigation water are:

Plant analysis includes tests on fresh tissue in the field and analysis of total nutrients in plants in the laboratory. Plant analysis is based on the relationship between nutrients in a plant and nutrient availability in a soil. Plant analysis is not a direct method of soil fertility evaluation, but it can serve as a valuable supplement to soil testing in the task of soil fertility evaluation. Plant analysis is useful in confirming nutrient deficiencies, toxicities and imbalance and identifying hidden hunger. Plant analysis generally provides more current plant-based information than soil testing, entails more effort in terms of sampling, sample handling and analysis and, perhaps, expensive.

A. Soil Sampling

Soil is a store house of several nutrients. These are present in available and reserve forms and a dynamic equilibrium always exists between these forms of nutrients in soil. If the available form of a given nutrient element is depleted by crop uptake or by any other means, there will be immediate replenishment from the reserve source. In this context, it is also appropriate to note that soil is not an eternal source of plant nutrients. In a bid to produce more, soils are exploited very badly and they are gradually becoming deficient in several nutrients. There are several soil related constraints coming in the way of achieving sustainability in crop production.

Soils of India vary widely among different regions. The first soil map of India was prepared and classified on the basis of existing knowledge of Russian pedological principles. Govind Rajan (1971) and Govind Rajan and Rao Gopal (1978) have discussed in detail the later developments on the preparation of soil map of India and giving the equivalents of different soil groups in US Comprehensive System of Soil Classification. Soil resource mapping was initiated in 1986 and in a span of 10 years (1986-1996), a detailed database in terms of soils, their area and extent, characteristics and grouping following soil taxonomy (Soil Survey Staff, 1999) was created. The present chapter on “soils of India-nutrient status and management concerns” takes into account the following aspects:

Plant nutrient disorders result from nutrient imbalances in soils. Nutrients are considered essential for plants, when it satisfies the following criteria (Arnon and Stout,1939):
    1.    The deficiency of the nutrient element makes it impossible for the plant to complete its life cycle
    2.    The deficiency of the element is specific and can be corrected only by supply of that element
    3.    The element is directly involved in the nutrition of the plant

Soil is the most precious basic natural resource, on which depends the security of food, nutrition, income, biodiversity, livelihood and environment. But, its indiscriminate and unscientific management is a major threat to sustainability of agriculture. Over the years, there is a loss in the productive potential of soils, which is attributed to imbalance in nutrient use, mining of nutrients from soil, poor replenishment, loss of carbon, pollution, decrease in biological activities, waterlogging, soil salinity etc. Thus, land use is not commensurate with land capability.

In this section we shall discuss diseases that do not involve any parasitic etiology. Such diseases are now more appropriately called ‘Disorders’. The disorder may be of many kinds but all of them have adverse effects on the normal physiology and total performance of the crop host. They are therefore, more often called ‘Physiological disorders’. Lack of proper soil and environmental conditions, nutrient status, irrigation factors and other parameters for successful crop cultivation may result in such disorders.

3.1 Damping-off Disease of Seedlings

The disease is quite common in nurseries or seedbeds all over the world. It is virtually a serious threat to almost all the nursery crops of vegetables and other crops including tomato, chillies, cauliflower, cabbage, brinjal, cucurbits, tobacco and a number of other crops. The economic importance of the disease is more because it takes the toll of precious seedlings in the very initial stages of the crop cultivation. The seed can become infected with a fungus which may cause darkening and softening of the seed leading to its decay. Similarly, seedlings may also be infected while sprouting or even after emergence. The disease is more serious in heavy soils with poor drainage. Abundant soil moisture with 90-100% humidity and temperature around 200C is favourable for the disease.

2.1 Loose Smut of Wheat

The disease is prevalent in all the wheat growing areas in the world. However, it is a serious problem in humid and sub-humid areas. The incidence of the disease is comparatively more in cooler and humid parts of northern India as compared to the drier and tropical parts of the country. Being a simple interest disease epidemiologically, this is a threat to the cultivation of wheat for seeds. The disease is therefore, dreaded by seed growing agencies who have to treat the seeds with costly chemicals.

A disease is characterized by the sum total of symptoms as expressed by the host plant and the signs of the pathogen involved. As stated earlier, it is the core part of disease diagnosis because in every diseased plant there are some symptoms/signs of the problem regardless of the ease in their visibility. Even in latent infections there are certain clues or at least presence of the pathogen inside the host serves as sign of the pathogen. However, the term, ‘disease’ itself refers to an uncomfortable situation of the concerned host. It reflects in the form of reduction in the vitality and performance of the host to varying degrees depending on the quality and quantity of the factors involved in production of the disease. Study of the characteristics of disease is, therefore, important for its quick and accurate identification.

Chemicals in the form of insecticides ,fungicides and herbicides are extensively used in large numbers in agricultural production. Commercial production of some crops would be impossible if chemicals are not used. Small quantities of chemical residues often remain in such crops and the harvested grains and other products. The residues of pesticides  have been observed in small quantities (ppm level) in soil, water, agricultural produce  and even in animal tissues and their products like meat and  milk. They finally reach the consumer, namely, man (and even animals). Even the environment  is  now-a-days polluted with pesticides and other chemicals harmful to the humans. In view of the importance and seriousness of the problem the residues need to be estimated in the food and non-food products to assess their safety. Analytical details of a few pesticide residue procedures are presented below. Specialized texts may be consulted for  more extensive information.

Plant pigments impart colour to the different components like leaves, flowers, fruits etc. They in turn are responsible for the colour of raw food, we eat. Pigments like chlorophyll, anthocyanins, flavonoids, tannins, xanthones etc. are the different pigments that are present in plants. The primary function of pigments in plants is photosynthesis, which uses the green pigment chlorophyll along with several red and yellow pigments that help to capture as much light energy as possible. Chlorophyll is green in colour. Carotenoids like a, b, and g, carotenoids are yellow in colour. Lycopene is red in colour. Flavones and falvonols are also yellow in colour. Anthocyanins are purple and magenta in colour. Other functions of pigments in plants include attracting insects to flowers to encourage pollination. The assay of pigments is mostly based on their native colour.

Sixteen chemical elements are known to be important to a plant’s growth and survival. The sixteen chemical elements are divided into two main groups: non-mineral and mineral.  The Non-Mineral Nutrients are hydrogen (H), oxygen (O), and carbon (C). These nutrients are found in the air and water.
  
In a process called photosynthesis, plants use energy from the sun to change carbon dioxide (CO₂ - carbon and oxygen) and water (H₂O- hydrogen and oxygen) into starches and sugars. These starches and sugars are the plant’s food. Since plants get carbon, hydrogen, and oxygen from the air and water, there is little the farmers and gardeners can do to control  how much of these nutrients a plant can use.

Alkaloids are of plant origin and are alkaline in reaction. They contain N as part of a hetercyclic ring. They exhibit pharmacological activity. Presently more than 2000 alkaloids are known. They have a lot of uses in medicine and as  flavoring agents, psychoactive agents, pain killers and as pesticides.

Certain constituents associated with plants are toxic. When such items are consumed by men and animals, they become hazardous. Mold growth on food items may be the cause of toxicity. Some of them are called mycotoxins. Aflatoxins are the best examples of such a group of compounds. Sometimes processing also produces some toxins. Fumigants, smoke and some metals (mercury, lead, cadmium, arsenic etc.) used for such purposes are some such toxic constituents. Pesticides used in protecting the crops and grains during storage remain on the items and the residues are hazardous.

Phenol is normally a benzene ring containing an –OH group, and hence an aromatic alcohol. The term “phenolic” refers to similar aromatic compounds with one or more -OH groups. Phenolics constitute one of the most widespread classes of secondary metabolites. Commonly talked about class of compounds like anthocyanins, flavonoids, lignins, tannins, coumarins and chalcones are all phenolic substances. Phenolics are water insoluble substances. However, the water solubility increases with the increase in the number of -OH groups. Phenolics absorb electromagnetic radiation strongly. Many of the phenolics absorb in the visible part of the spectrum (Ex. anthocyanins) and are coloured. Phenolics are produced in plants by 1. Shikimate pathway through phenylalanine (C₆-C3) and 2. Acetate/malonate pathway.

Vitamins are essential organic nutrients required by an organism in small quantities. They are essential since they cannot be synthesized in sufficient quantities by an organism, and must be obtained from the diet. The term vitamin does not include other essential nutrients like dietary minerals, essential fatty acids, or essential amino acids which are needed in larger quantities than vitamins. The term vitamin is derived from “vitamine,” coined in 1912 by the Polish biochemist Funk. The name is from vital and amine, meaning amine of life. Thirteen vitamins are generally recognized presently. Vitamins are used in small quantities by an organism to keep it in a healthy condition.

Nucleic acids were first discovered in 1868 by Friedrich Meischer. Nucleic acids are high molecular weight polymers that are present in our cells. They store and transfer genetic material from generation to generation. Knowledge of how genes are expressed and how they can be manipulated is becoming increasingly important for understanding of nearly every aspect of biochemistry. These macromolecules p ass on information for cellular growth and reproduction. All the genetic information in the cells is called the genome. Every time a cell divides, the information is copied and passed on to the new cells.

Enzymes are organic catalysts produced by living organisms. They make possible biochemical reactions. Hence they are called biocatalysts. They are mostly a specialized class of proteins. However, there are some non-protein enzymes like ribozymes, which are RNAses. Enzymes speed up reactions at ambient temperatures. This is in contrast to chemical reactions like saponification of lipids which take place when lipids are boiled for a few hours with concentrated alkali. Enzymes, namely, lipases, hydrolyze lipids at body temperatures in minutes. They are superior to chemical catalysts by a factor of 10⁷ to 10¹⁴ . An enzyme may be a simple protein or a complex protein. They are produced by cells and are mostly globular proteins. Each cell contains an estimated 3000 different enzymes.