eChapters

Plant competition is a powerful force for the elimination of some weaker plants. Plants require nutrients, water, light, Oxygen and Carbondioxide for their growth and development. Weeds compete with the crop for growth factors and the competition is maximum at the early growth stages of the crop. But the competiting ability of the weeds becomes practically nil as soon as the crops attain maturity. Weeds need more nutrients and water than the crop plants. The weeds in general grow faster and shade the crop plant if they are not controlled at proper time and afterwards interfere in the growth of crop plant. Weeds have allelopathic effect on crop growth. Some weeds excrete certain chemicals into the soil which inhibit the germination and growth of other plants in their vicinity and the phenomenon is called allelopathy. Allelopathy is defined as the direct or indirect harmful effects of one plant on another plant through the production of chemical compounds that escape in the environment.

Weeds interfere with man’s utilization of land and water in various ways. The extent of losses depends on the intensity, infestation, time of occurance and type of weeds.

1. Competition between weeds and crops for growth factors

Weeds compete with crop plants for  other factors in the micro-enviroment. Weeds are capable of absorbing more amount of nutrient from soil than the crop plants. In dry lands, weeds exhaust the soil moisture and put the crop under water stress earlier and thus reduce the yield. Weed can compete with productive crop or pasture land or convert the productive land into unusable scrub. Weeds are also often poisonous, produce burrs, thorn or other damaging body parts or otherwise interfere with the use and managemet of desirable plants by contaminating  harvest or excluding livestock.

There are some weeds which prefer to in crop field and some of them have a distinct association with some crops.

Dispersal means the spreading of weeds from one place to another place. Dispersable of weeds generally takes place through seeds and vegetative parts. Dispersal of mature seeds and live vegetative parts of weeds is nature’s way of providing non-competitive sites to new individuals.

    (a)    Dispersal of weeds through seeds: Seeds are protector and propagator of their kind. Weeds seeds remain viable for a long time and their dispersable mainly takes place through natural and human agencies.

No plant in the earth is completely worthless. Weeds have also some beneficial effects although they do much harm in different ways. The beneficial effects of weeds are as follows:

    1.    Most of weeds absorbs nutrient from the deeper layer of soil. When such weeds are incorporated in the soil, they add organic matter content of the soils. As a result, the fertility of plough layer from where plants absorb most of their nutrients is enriched.

    2.    Weeds help in controlling erosion by the soil binding effects of their roots and by forming a living mulch, which resist beating action of rain drops and sweeping action of wind.

Weeds have some characteristics as follows:

    1.    Weeds are hardy and can grow under adverse edaphic (Soil), climatic and biotic condition.
      Example: Lantana camera,Eupatorium adoratum etc.

    2.    Weeds in general prolific with abundant seed production potentialities.
        Example: Amaranthus viridis, Chenopodium album etc.

Ecology is the inter-relationship between organisms and their environment. Weed ecology is study of inter-relationship between weed and their environmneent. Simply, Ecology of weeds means the inter-relationship of weeds with climate, soil, crops and other biotic factors. Terrestrial weed species persist in the soil by virtue of dormant structures, typically seeds or vegetative perennating organs such as rhizomes, tubers and taproots. In dense infestations, the banks of seeds or underground meristems from which new plants may be recruited into adult populations can be exceptionally large. Rao (1968) estimated that in Cyperus rotundus L. tuber populations of 10 million per hectare were possible, whilst Soerjani (1970) calculated that Imperata cylindrica may annually produce six tones of rhizomes per hectare. Typically seed banks of annual weeds in arable soils contain from 1000-10,000 seeds per m2whilst in grassland the upper limit to this range may extend at least to 1 million per m² (Mortimer 1994).

1. Classification of weeds based on life cycle (Ontogony)

(i) Annuals: Weeds that  complete their life cycle within a year or season are called annual weeds. They are associated with annual crops and propagated mainly through seeds. Annual weeds are subdivided according to the season of prevalence as follows:

(a) Kharif season  annuals or Kharif  weeds: The weeds that grow during the summer and complete their life cycle during Kharif or rainy season are called Kharif season annuals or Kharif weeds. The kharif weeds complete their life cycle during the warm wet season (i.e. from the month of June to September) and attain maturity with the onset of winter and finally dies.

Weeds are the plants which grow where they are not wanted or simply plants growing out of place. A plant may be desirable in one situation and a weed in another situation. Those plants that interfere with human activity in crop and non-crop areas are considered weeds. Weeds compete with crops for soil nutrients, water and light; they host insects and plant pathogens harmful to crop plants, and their root exudates and/or leaf leachates may be toxic to crop plants. Weeds also hinder crop harvest and increase the costs of such operations. In addition, at harvest, weed seeds often contaminate the crop produce. Thus, the presence of weeds in crop areas reduces the efficiency of inputs such as fertilizer and irrigation water, enhances the density of other pest organisms, and finally severely reduces crop yield and quality (Labrada and Parker 1999).  Weeds are serious menace in crop production.

Origin and Concept of SHGS
    
The origin of SHGs is from the brainchild of Grameen Bank of Bangladesh, which was founded by Mohammed Yunus.  SHGs were started and formed in 1975.  In India NABARD is initiated in 1986-87.  But the real effort was taken after 1991-92 from the linkage of SHGs with the banks.  A SHG is a small economically homogeneous affinity group of the rural poor voluntarily coming together to save small amount regularly, which are deposited in a common fund to meet members emergency needs and to provide collateral free loans decided by the group (Jha 2000).  They have been recognized as useful tool to help the poor and as an alternative mechanism to meet the urgent credit needs of poor through thrift (Rao 2002) SHG is a media for the development of saving habit among the women (Rajamohan 2003).  SHGs enhance the equality of status of women as participants, decision-makers and beneficiaries in the democratic, economic, social and cultural spheres of life.  (Jain 2003).

Almost two third of India’s population does not have access to formal financial services. The women self help movement emerged as an important strategy for achieving financial inclusion, contributing to inclusive growth and generating social capital in order to address larger issues like poverty eradication and women empowerment. Self Help Group (S.H.G.) are proving to be the most effective instruments for financial inclusion. The experiments started some thirty years ago with N.G.O.s Piloting S.H.G. promotion, which has evolved into a national movement with the proactive role of the state governments- gaining recognition from all the major stakeholders. S.H.G.s are also helping to optimize the utilization of the India’s vast formal financial institutional structure of 160,000 institutions in the rural areas through linkages with banks and acting as business correspondents for the banks.

Introduction

Sustainable development has caught the imagination and action all over the world for more than a decade and sustainable agriculture is necessary to attain the goal of sustainable development. According to the Food and Agriculture Organization (FAO), sustainable agriculture “is the successful management of resources for agriculture to satisfy changing human needs while maintaining or enhancing the quality of environment and conserving natural resources”. All definitions of sustainable agriculture lay great emphasis on maintaining an agriculture growth rate, which can meet the demand for food of all living things without draining the basic resources.

Laboratory animal science (LAS) advances scientific understanding of the care and use of animals that play a key role in research supporting the development of biomedicine. National and provincial laws, regulations, guidelines and standards apply to quality control and licensing, quarantine and infectious disease control, breeding and husbandry, transgenic animals, staff qualifications, animal welfare, imports, exports and transportation.   Regulation and oversight of lab animal use are the responsibility of the National Ministry of Science and Technology, provincial departments of science and technology, and institutional animal care and use committees.

The major challenge of the present time in agriculture is implementing sustainable development and meeting the food needs of increasing population simultaneously. Agricultural extension always remains an integral part of National Agricultural Policy. At present, agricultural extension has a crucial role to play in the context of growing demands of agricultural production in a sustainable manner. In this situation extension’s traditional task of transferring and disseminating appropriate technologies and agronomic practices would not be sufficient. There is need to view extension for sustainable development in an institutional strengthening context, both in functional and structural.

Introduction

Seabuckthorn (Hippophae Spp) a treasure house of vitamins, belonging to the family Elaeagnaceae, and it is a valuable medicinal plant, since its fruit contain high amount of bioactive substances. It is a thorny, temperate bush, tree and is widely distributed throughout the dry temperate regions of Europe and Asia. As the name indicates Seabuckthorn, the plant grows from sea level to high altitude mountain regions but mainly distributed in higher elevations of Indian Himalayas, from Ladakh (J & K) to Lahaul - Spiti (H.P.), Kumaon and Garhwal in Uttarakhand, Sikkim and Arunachal Pradesh (Chauhan 1999). It is seen under natural conditions Seabuckthorn grows on slopes, well drained soil with silt, river banks, lakes, sea shores & waste lands. It is well adapted to dry conditions. Seabuckthorn the wonder plant of cold arid Himalaya, grows in wastelands, dry rocks and along river belts in Indus, Nubra, Chanthang, Suru, zanskar and Lauhal - Spiti valleys in India (Singh and Chaurasia 2000).

Biotechnology is one of the most exciting and revolutionary sciences of 21st century. According to Convention on Biological Diversity, biotechnology is defined as “any technological application that uses biological systems, living organisms, or derivatives thereof, to make or modify products or processes for specific use”. Biotechnology has proven its immense applications at every step of human life such as, health care, crop improvement, development of valuable products and abatement of environmental problems. Agricultural biotechnology is the area of biotechnology involving its applications to agriculture. Agricultural biotechnology has been practiced for a long time, as people have sought to improve agriculturally important plants/ organisms by selection and breeding.

Introduction

India produces 77.51 million tones of fruits of which only 10-20% are processed and rest are used as fresh (Singh 2010).  The post harvest losses are estimated to be in the order of 20-40%.  In terms of value it exceeds Rs.2000/- crores annually (Chadha 1989).  Processing of fruits under arid conditions is all the more important due to non-availability of fresh produce throughout the year in rural areas.  However, the area and production under arid fruits are increasing day by day in the states of Rajasthan, Haryana and Gujarat.  As a result seasonal glut has started in the local market and growers are not able to get the remunerative prices of their produce. In our country over 70% of the Indian population resides in village and are engaged mainly in farming and related activities besides their exclusive involvement in domestic work. Keeping above points in view, Agro-based technology should be developed for rural masses to create gainful employment by increasing the productivity through value added processed from arid fruits.

Introduction

Medicinal and aromatic plants constitute a major segment of the flora, which provides raw materials for use in the pharmaceuticals, cosmetics, and drug industries. The indigenous systems of medicines, developed in India for centuries, make use of many medicinal herbs. These systems include Ayurveda, Siddha, Unani, and many other indigenous practices. More than 9,000 native plants have established and recorded curative properties and about 1500 species are known for their aroma and flavour. In one of the studies by the World Health Organisation, it is estimated that 80 per cent of the population of developing countries relies on traditional plant based medicines for their health requirements (WHO 1991). Even in many of the modern medicines, the basic composition is derived from medicinal plants and these have become acceptable medicines for many reasons that include easy availability, least side effects, low prices, environmental friendliness and lasting curative property. India and China are the two major producing countries, having 40 per cent of the global biodiversity and availability of rare species. These are well known as the home of medicinal and aromatic crops that constitute a segment of the flora, and provide raw materials to the pharmaceutical, cosmetic, fragrance, flavour etc. industries.

The contribution of agro biodiversity to world agricultural production is immense. The world agricultural landscape is now dominated by few crops and varieties. This agricultural scenario is suicidal because the homogeneous plant population is vulnerable to biotic and abiotic stresses. The ecosystems rich in biodiversity possess greater resilience and hence able to recover more readily from biotic and abiotic stresses, such as drought, environmental degradation, pests, diseases, epidemics, etc. Hence, a decline in biological diversity puts the functioning of ecosystems at risk. The cultural value of biological diversity conservation and sustainable management for present and future generations is another important reason for conserving it for posterity. To tide over the precarious condition of food insecurity, rich crop germplasm must be sustainably managed to tap the potential of crop genetic resources. The sustainable management of agrobiodiversity is therefore very essential for developing adaptation strategies in the era of global climate change.

Mites have been known as pests of agricultural and horticultural crops since long but now they rank as very serious pests and vectors of many plant diseases. The application and extensive use of pesticides, fertilizer and improved cultural methods have probably favoured increase of the population. Mites as crop pests are confined to certain group of the other acari. Near about 20,000 species have been described of the total mite fauna on a world basis. From India, 660 species of phytophagous mites have been described and nearly 30 species are reported as potential pests (Gupta 1987). Phytophagous mite belongs to family - Tetranychidae, Tenuipalpidae, Tarsonemidae, Eriophyidae and Tuckerellidae. These mites cause direct damage like loss of chlorophyll, stunting of growth, defoliation, reduction in size and quality of fruits, appearance of various types of plant deformities etc. and all these severely affect the yield. Besides causing direct damages, few phytophagous mites inject toxic substances in to their hosts, which cause increased localized growth and disruption of tissue (Jeppson et al. 1975), and many species belonging to family – Eriophyidae are known to act as vectors of plant viruses. The dust entangled in the web formed by tetranychid mites on leaves prevent the sunlight reaching the leaf surface and as result photosynthesis is impaired, the leaves turn pale, yellow and fall down. This affects the vitality of the plant.

Introduction

The fast development of technology for increasing production ignoring the agroecosystem resulted in disturbed natural cycles. The result is visible in terms of unsustainabiliity in agroecosystem. In addition, increasing use of chemical pesticides for the management of soil-borne plant pathogens had caused pollution of soil, surface and ground water besides affecting the crop produce and ecosystem. The pendulum of public opinion once so favourable to chemical control has gone against chemicals and advocated phasing out the chemical pesticides. Revival of the natural balance is therefore needed for sustainable farming with eco-friendly methods such as bioagents/biopesticides, soil solarization, botanicals, etc. Organic farming is one such approach which emphasis on maintaining the natural cycle with eco-friendly approaches.

1. Introduction

In the field of sustainable agriculture our main aim to produce high quality, safe and affordable food for ever-increasing worldwide population. Today, global agriculture is at crossroads and this is the consequence of climatic change, increased population pressure and detrimental environmental impacts. Furthermore, agricultural growers and producers have the additional constraints of economic profitability and sustainability. During the last couple of decades excessive amounts of chemicals are used to improve plant health, productivity and for management of plant pathogens, which has disturbed the ecological balance of soil and has led to the depletion of nutrients. Therefore, there has been ever-increasing interest to develop new mechanisms to ensure food security through sustainable crop production system that will supply adequate nutrition without harming the agroecosystem. Plant growth in agricultural soil is influenced by many abiotic and biotic factors. There is a thin layer of soil immediately surrounding plant roots that is an extremely important and active area for root activity and metabolism which is known as rhizosphere.

Sustainable crop production depends upon the rational use of chemical fertilizers and pesticides along with organic manures for better soil health. Owing to the constant production of crops from the soil, the latter is being depleted gradually of its nitrogenous and other nutrients. An ordinary crop takes about 25 lb of nitrogen (N) from an acre. It is, therefore, necessary to replenish the soil with the elements, which are removed by the crops year after year. Moreover, in recent years increasing fertilizer costs, and concern for sustainable soil productivity and ecological stability in relation to use of chemical fertilizers, have emerged as issues of vital concern. Furthermore, heavy reliance on chemical fertilizers tends to favour economically those farmers with large hectarage. These considerations have led to a renewed interest in the biofertilizers and organic manures such as FYM, compost and green manures. Biofertilizers which are formulations of bacteria, blue green algae or fungi helps in sustainable agriculture production either by providing plants with fixed nitrogen, available P or by other plant growth promoting substances. Organic matter (OM) is the life of the soil because it contains all the essential elements required for plant growth.

Introduction

In India ,the increasing demographic pressure with developmental activities are causing tremendous pressure in utilization of natural resources leading to various kinds of ecological problems and land degradation. The Govt. of India has for long considers watersheds as catalysts for development activities in rain-fed areas. Watershed, simple stated as a manageable hydrological unit. Watershed development approach calls for an integrated effort of many courts, viz, area development, resource identification and management programme- planning, implementation and evaluation and also the disciplines and functionary involved. An integrated approach in watershed management, the development of agricultural land alone is not the criteria, but the development of the entire area covering a watershed from highest point (ridgeline) to outlet of the Nalah or natural stream will have to be considered.  For scientific development of watershed area, all natural resources such as water, land, human, vegetation, livestock, wildlife etc. have to properly identified, quantified, and appropriately utilized.

Though a large number of insect pests are reported to attack mango, which cause considerable damage to mango crops in India. More than 492 species of insects, 17 species of mites and 26 species of nematodes have been reported to be infesting mango trees, about 45 per cent of which have been reported from India. Almost a dozen of them have been found damaging the crop to a considerable extent causing severe losses and, therefore, may be termed as major pests of mango. These are hopper, mealy bug, inflorescence midge, fruitfly, scale insect, shoot borer, leaf webber and stone weevil. Of these, insects infesting the crop during flowering and fruiting periods cause more severe damage. The insects other than those indicated above are considered as less injurious to mango crop and are placed in the category of minor pests. A brief description of the biology and control of major pests of mango is given below. Mango suffers from several diseases at all stages of its life. All the parts of the plant, namely, trunk, branch, twig, leaf, petiole, flower and fruit are attacked by a number of pathogens including fungi, bacteria and algae. They cause several kinds of rot, die back, anthracnose, scab, necrosis, blotch, spots, mildew, etc. Some of these diseases like powdery mildew are of great economic importance as they cause heavy losses in mango production. Major pests and diseases of mango and their control measures are discussed below.

Nursery is a place like a crèche, where young tender seedlings are nurtured before planting in the field. The healthy, sturdy, vigorous and diseas free seedlings can establish well in competitive environment. Generally, vegetables like tomato, brinjal, chilli, pepper, cauliflower, cabbage, knol khol, lettuce, onion, Brussel’s sprouts are raised through seedlings. But skyrocketing cost of hybrid seeds and high premium of early harvest warrant the attention of cucurbits growers to produce the nursery, Nursery raising has certain advantages over the direct seeding like:

Introduction

Seed is regarded as carrier of new technologies. Therefore, the seed needs to be protected so as to deliver it as an efficient input. When seed is planted during an environmental stress like heat or drought chemical reactions in the seed may not go as smoothly as when the seed is under little or no stress. All the crops are liable to face varying degree of water stress and it is most crucial at the time of germination and plant establishment. Successful stand establishment under all conditions is the key to assured production. The early sown varieties of various crops faces the problem of heat stress at early vegetative stage. Moreover, due to global warming there is uncertainty regarding the physiological response of crops to enhanced atmospheric temperature. Any significant change in climate on a global scale directly affects crop production and then would impact local agriculture.

Introduction

The increasing concern about the long-term productivity of agro ecosystems has emphasized the need to develop a management strategy that maintains and protects the soil resources. This is directly related to the maintenance of the level of soil organic matter and nitrogen status, which are the critical components of soil productivity. These parameters can change over time due to crop management practices such as cultivation, crop rotation, residue management or fertilization which, in turn, can influence the long-term sustainability of ecosystem. Application of chemical fertilizer is one of the most expensive inputs in agriculture. About 65% of the applied nitrogenous fertilizer is lost from the plant–soil system through gaseous emissions, runoff, erosion and leaching which causes greenhouse effects and nitrate pollution of surface and ground water (Rejesus and Hornbaker 1999). Similarly, P applied in soil is rapidly fixed and results in low P availability for plant production. In this context, the deployment of microbial biofertilizers promise increasing soil nutrient availability in integrated nutrient management system.

Vegetable occupy an important place in diversification of agriculture and have played a pivotal role in food and nutritional security of ever growing population of our country. The vegetable requirement of our country is estimated at 225 million tonnes by 2020 (Paroda, 2020) against only 134 million tonnes in 2009-10 (NHB, 2010). India is facing, today, with stagnation in crop productivity and slows down in agricultural growth. Declining soil health and fertility is considered as one of the factor for such a decline. The restoration of soil health and fertility is, therefore, a formidable challenge before us to ensure higher and sustainable productivity, profitability and national food and nutritional security.

Indian crop production system excels in front of several biophysical adversities commonly known as biotic and abiotic stress.  Water is the principal factor limiting crop yield and about 2/3 of total cultivated landing India comprise of Dry land agriculture primarily under rainfed conditions with no or limited water supply system.  The Indian production systems are dominated by cereals, primarily rice maize, sorghum, pearl millet other coerces and fine cereals leguminous (urd bean, mung bean, peanut) and oil yielding crops during kharif and  wheat barley chickpea, lentil and forage legumes in rabi  season.  The production systems are generally characterized by cereal/legume mixed-cropping dominated by maize, millet, sorghum and wheat. The major constraints in both regions to crop production are low soil fertility, insecure rainfall, low-productive genotypes, low adoption of improved soil and crop management practices, and lack of appropriate institutional support. choice of crop  is important but selection of right varieties is utmost  important because  varieties which have proven excellent in irrigated or high rainfall areas are generally not suited for limited irrigated conditions.

Introduction

Under the present scenario of growing human population and shrinking land and water resources for agriculture, expanding abiotic and biotic stresses, increasing genetic erosion; relentless efforts are needed to enhance the plant productivity as well as quality of produce. In fact, improvements in agricultural production as well as food and nutrition conditions depend on land, water and energy resources, which are, undoubtedly, limited and depleting at a rapid pace.

Biotechnological innovations in conjunction with conventional technologies have opened new frontiers in agriculture thereby offering exciting opportunities for increased sustainability and profitability in agriculture. Thus, biotechnological tools complement (rather than replace) the traditional methods used to enhance the agricultural productivity to cater to the needs of third world agriculture (Swarup and Srivastava1990, Rao et al. 1996).

Fisheries
DSIR/TPDU/TIF 056 and E-28-GO-GOI Research Scheme on “Documentation and Preservation of Agricultural Traditional Knowledge through Farmer Participatory Approach”

Medicinal Plants
DSIR/TPDU/TIF 056 and E-28-GO-GOI Research Scheme on “Documentation and Preservation of Agricultural Traditional Knowledge through Farmer Participatory Approach”

Agricultural Tools
DSIR/TPDU/TIF 056 and E-28-GO-GOI Research Scheme on “Documentation and Preservation of Agricultural Traditional Knowledge through Farmer Participatory Approach”

Seed Storage Structures
Seed Storage Structure
Kuluppai / Kulumai (Mud Pot)
Th. Gopalakrishnan, 52 years old is residing in A.Edayapatti village in Manapparai taluk of Trichy district. He is educated up to 10^th standard and has agriculture as his primary occupation. He possesses a post harvest storage structure called ‘kuluppai/kulumai’.

It is a storage structure used to store grains, which is suited to all ecosystems. This structure is invented by ancestors and maintained for more than 100 years until now. 

Post Harvest Methods
DSIR/TPDU/TIF 056 and E-28-GO-GOI Research Scheme on “Documentation and Preservation of Agricultural Traditional Knowledge through Farmer Participatory Approach”

Crop Protection Measures
DSIR/TPDU/TIF 056 and E-28-GO-GOI Research Scheme on “Documentation and Preservation of Agricultural Traditional Knowledge through Farmer Participatory Approach”

Crop Management Practices
DSIR/TPDU/TIF 056 and E-28-GO-GOI Research Scheme on “Documentation and Preservation of Agricultural Traditional Knowledge through Farmer Participatory Approach”

Traditional Varieties

This chapter contains the description of the Indigenous Traditional Knowledge practices as subject wise manner viz, Traditional varieties, Crop management, Crop protection measures, Post harvest methods, Storage structures, Farm tools, Medicinal plants, Ethnoveterinary practices, Fisheries and others related to agriculture.

Warren (1987) defined indigenous knowledge as local knowledge, knowledge that is unique to a given culture or society. This knowledge is the information base for the society, which facilitates communication and decision making. Indigenous knowledge is passed down from generation to generation by word of mouth.
 
Carter (1988) while describing the nature of indigenous knowledge indicated that IK is highly localised and restricted. Local environmental factors and cultural conditions govern the revolution of IK these vary between countries, regions and even farm to farm.

India over several millenniums has been the treasure land of biological wealth, intellectual knowledge and spiritual wisdom. During both pre and post Vedic periods, arts, science and technology had flourished well in various fields. Indian agriculture to some extent is much traditional and dates back to about 10,000 years. India with its traditional crop varieties and crop production technologies was able to feed its population and also exporting some selected produces to other continents. All the Indian villages had been the self sufficient, self sustained and self reliant units. The development of modern agricultural production was achieved by creating large scale specialized farm production units, increased mechanization and use of chemical inputs.

Heat units also called growing degree-days (GDD), effective heat units, or growing degree units, are a heuristic tool in phenology. GDD is a simple means of relating plant growth, development and maturity to air temperature. The concept is widely accepted as a basis for building phenology and population dynamic models. Degree day units are often used in Agrometeorology, Agronomy, Entomology and Pathology essentially to estimate or predict the lengths of the different phases of development in crop plants, insects, pathogens etc.

The agro-meteorological data after the quality control is used to establish a relationship between the crop and weather or to understand their interactions. In agrometeorological data analysis, statistical tools are used. The frequent use of statistics terms and their computational formulas are given below for ready reference:

Weather has profound influence on agriculture, which demands that the changes in weather conditions are regularly monitored. In qualitative terms, weather conditions are often expressed on the basis of final condition created by interaction of different components. For example, too hot, too cold, sunny or cloudy, humid, dry weather conditions refer to specific atmospheric conditions but are least useful in analyzing the impact of weather on agriculture.
 
The measurements taken at a weather station can include any number of atmospheric observables. The WMO has laid down specifications, procedures and practices in respect of various meteorological matters such as instruments, observations, telecommunications, processing of data, analysis etc.

Weather phenomena are not localized, it moves and varies over space and time. The weather over a place or area is the result of far away weather events/conditions. Acquisition of global scale observation, therefore, becomes a pre-requisite for understanding the physics of the weather and also to represent the weather condition over an area at a particular time. Complex three-dimensional models of weather systems can be made by collecting weather data at multiple levels in the atmosphere. Upper-air data are important to know present weather over a place and crucial for weather forecasting.

Real time weather data at different time intervals is very important for the crop weather studies, but through the agro-meteorological observatories such real time weather data are generally not collected. The acquisition of agro-meteorological data through conventional observatories requires services of trained personnel to collect, compile and creation of weather data base. With the advances in technology, weather observations are automatically recorded, stored and can be transmitted to the remote place with the help of Automatic Weather Station (AWS).

Evapotranspiration (ET) is the combined loss of water from vegetation and soil. When water is not a limiting factor at a site, the rate of ET is primarily controlled by meteorological factors like solar radiation, temperature, wind and relative humidity. The measurement of ET under natural conditions is of great importance in the water resource management and irrigation planning. Potential evapo-transpiration (PET) is the evaporation from a surface if water was never a limiting factor. PE-can also be calculated using empirical formulae.

The information on soil-water content is necessary from the point of view of efficient water management of crop production as water required by crops is to be met from the water stored in their root zone. Soil water content changes periodically as a result of changes in field water balance components namely, precipitation, irrigation, evapotranspiration, runoff and deep percolation. Crop growth is adversely affected if the soil water depletes below certain level. For selection of crops, deciding of irrigation level and frequency of irrigation, the assessment of water content of soil is important.

Water loss from a plant in the form of vapour is known as transpiration. Loss of water vapour mainly from leaf cells through pores but also from the leaf cuticle and through lenticels of the stem. The resistance to diffusion of water vapour through a plant’s stomata is called as stomatal resistance. Whereas, stomatal conductance is a numerical measure of the maximum rate of passage of either water vapour or carbon dioxide through the stomata, or small pores of the plant.