eChapters

Site-specific weed control technologies practiced in precision farming are defined as machinery or equipment embedded with technologies that detect weeds growing in a crop and take action to maximise the chances of successfully controlling them taking into account predefined factors such as economics.Some of the commercial hardware and software developed for precision agriculture practices comprise tools for weed mapping and control software that adapts spraying to local weed occurrence. However, few farmers have adopted sitespecific weed management, although several studies have shown that weed occurrence and density varies significantly within a farm or a field. Site-specific weed control techniques have gained interest in the precision farming community over the years. Managing weeds on a subfield level requires measuring the varying density of weeds within a field. Decision models aid in the selection and adjustment of the treatments, depending on the weed infestation. The weed control can be done either with herbicides or mechanically. A site-specific herbicide application technology can save large amounts of herbicides. Mechanical weed control techniques adapting to the weed situation in the field are applicable to a wide spectrum of crops.

A system for the discrimination of different weed species and crops from images is done which generates weed maps automatically. Models for the yield effect of weeds are developed and applied in on-farm-research experimental setups. Economic weed thresholds are derived and used for an herbicide application with a patch sprayer.Herbicide use has not eliminated weed problems in agriculture and the need for manual weed removal is still an issue within specialty crop systems, particularly during the first several weeks of crop emergence when competition for resources is greatest.

Precision agriculture is a powerful technology with potentially important applications to weed management. However, growers should remember good agronomic practices, including preventing weed infestations, managing herbicides wisely to prevent resistance, and minimizing environmental impact associated with weed management. Weeds, and methods used to control weeds, can have negative economic and environmental impacts. With precision agriculture, growers can take advantage of the patchy nature of weeds by targeting management efforts only where they are needed instead of wasting expensive and potentially hazardous inputs where weeds are not present. Weeds are patchy because weed spread, survival, and reproduction are variable within a field and over time. Weed patches stay in about the same place from year to year, even though weed density within a patch may vary

Precision agriculture is yet to be popularized for taking its enormous advantages. In laser land levelling and micro irrigation/ fertigation it must have made its prominence but others it is with research institutes where research is focussed on the spatial variability of production environments, development of efficient and suitable data management systems, efficiency of various types of image analyses and optical sensing, efficiency of sensors and related technologies, designs of precision agriculture equipment, optimal inputs and service uses, and their spatial allocations, potentials of unmanned aerial vehicles (UAVs), nanotechnologies and several others.The adoptions of precision-agriculture technologies have, so far, mostly been limited to parts of developed countries. Major contributions to the profitability of precision agriculture is reduced costs of plant protection inputs and higher output revenues.

Plants require proper environment for its growth and development. If environment is not suitable crop would not do well. To ensure proper environment to commercial crops for their better growth and development covered structures are used which provide microclimate appropriate for their growth and development. Growing of crops under such protective structures, also known as greenhouses, is termed as greenhouse technology. The structures harness solar radiation for photosynthesis in plants or can be provided with artificial lights (LEDs) for the purpose. The technology embraces many aspects of farming such as modelling of structures, agronomic practices for the production of the crop and the commercial viability of the venture. The technology ensures crop production in a cover more or less independent of natural prevailing environment. The covering or cladding permits desirable aspect of sun and air and help in modifying crop production environment inside. The modification of environment is aimed of creating micro-climate inside the structure/greenhouse most appropriate for the growth and development of the crop.

Hence greenhouse can be defined as a framed or inflated structure with claddings like glass polyethylene sheets, poly carbonates, fibre reinforced plastics and others in which plants are grown by creating microclimate conducive to crop for its growth and development with or without automation and mechanization. The purpose of growing crops under greenhouse conditions is to extend their cropping season and to protect them from adverse environmental conditions, such as extreme temperatures, precipitation and pests. A large number of greenhouses/poly houses have come up in almost all states of India. Though in infancy but greenhouse cultivation particularly in horticulture crops and nursery production is visible.

Different types of greenhouses or protected structures are designed to meet the specific needs. They can be classified based on shape, utility, construction, cladding material, net houses and technology adopted.

A. Classification based on shape of greenhouse: Greenhouses can be classified based on their shape or style. For the purpose of classification, the uniqueness of the cross section of the greenhouses can be considered as a factor. As the longitudinal section tend to be approximately the same for all types, the longitudinal section of the greenhouse cannot be used for classification. The cross sections depict the width and height of the structure and the length is perpendicular to the plane of cross section. Also, the cross section provides information on the overall shape of the structural members, such as truss or hoop, which will be repeated on every day. The commonly followed types of greenhouse based on shape are lean-to, even span, uneven span, ridge and furrow, saw tooth and quonset.

Lean-to type greenhouse: A lean-to design is used when a greenhouse is placed against the side of an existing building. It is built against a building, using the existing structure for one or more of its sides. It is usually attached to a house, but may be attached to other buildings. The roof of the building is extended with appropriate greenhouse covering material and the area is properly enclosed. It is typically facing south side. The lean-to type greenhouse is limited to single or double-row plant benches with a total width of 7 to 12 feet. It can be as long as the building it is attached to. It should face the best direction for adequate sun exposure. The advantage of the lean-to type greenhouse is that, it usually is close to available electricity, water, and heat. It is a least expensive structure. This design makes the best use of sunlight and minimizes the requirement of roof supports. It has the following disadvantages:

Application of greenhouses in agriculture is mainly to modify microclimate for the production of crops with multiple objectives of raising crops in season offseason, round the year, early crops, late crops, breed crops, raise genetically engineered plants, seed production so and so forth. With hi-tech agriculture and modern techniques greenhouses are used for growing crops anywhere and everywhere, on soil under soil, water, under water and space. Greenhouses are mainly used for crop nursery production, crop production largely in vegetables, flowers and herbs. Among fruits mainly strawberry is grown under greehouses commercially. Other fruits can also be grown.

Besides crop production greenhouses are used for dehydration or drying of produce, seed production, for crop improvement using biotechnology and other sciences. Use of greenhouses in uncongenial environments for crop production is common in places like high altitudes, deserts, arctic climate and alike. One of the largest greenhouse complexes in the world is in Almería, Andalucía, Spain, where greenhouses cover almost 200 km2 (49,000 acres). One of the important use of greenhouses world over is raising tissue culture plants through a popularly known process hardening. For hardening of tissue culture plants different types of low and high technology greenhouses are must. Greenhouses in hot, dry climates used specifically to provide shade are sometimes called shade houses. Hydroponic crop production is generally done in greenhouses. Greenhouses are also used as retail market centres mainly for ornamental plants and seedlings and grafts of horticultural crops. Greenhouses are used for maintaining bee (honey bees and bumble bees) colonies as crop pollinators.

Many crops can be grown in greenhouse but the choice depends on number of factors.

1.Requirement of the farmer, what for she/he wants to grow the crop.

2.For personal use number of vegetable crops and herbs and fruits like strawberry and papaya can be grown.

3.In case of commercial crops, the market must be ascertained before the choice of the crop.

4.Greenhouse must be equipped to create micro-climate for the crop of choice.

5.The choice of crop is a crucial factor for the economic feasibility and success of a commercial greenhouse operation. The revenue of cultivated crop makes the venture to progress.

6.Crop varieties, suitable for greenhouse cultivation should differentiate themselves from open-field varieties to fetch better price on quality.

The productivity of a crop is result of genetic make-up (heredity) and environment (climate) and their interaction. The components of crop environment or climate or microclimate are light, temperature, air compositions and the nature growing medium or soil. In open fields, only manipulation of nature of the soil or root medium by tillage, irrigation and fertilizer application is possible. Under greenhouse structure control of any one or more of the components of the micro climate is manipulated.

Light

The visible light of the solar radiation is a source of energy for plants. Light energy, carbon dioxide (Co2) and water all enter in to the process of photosynthesis through which carbohydrates are formed. The production of carbohydrates from carbon dioxide and water in the presence of chlorophyll, using light energy is responsible for plant growth and reproduction. The rate of photosynthesis is governed by available fertilizer elements, water, carbon dioxide, light and temperature. The photosynthesis reaction can be represented as follows

Soil is the main growing medium. Natural as well as synthetic substitutes to soils are cropping up. Under greenhouse cultivation growing medium is generally top soil as used in open field/traditional farming. The practices of soil preparation for planting crops are more or less same as under open field. Generally, crops are planted on raise beds. As under open conventional farming soil preparation are made as per the crops or their varieties/hybrids to be grown. To enrich the soil with nutrients soil is tested for its physical and chemical properties and amended accordingly keeping in view the crop requirement. The soil composition is checked with each crop cycle and amended as per requirement of next crop. To avoid the harmful microbes and insects build up in the soil it is advisable to solarize or fumigate the greenhouse soil each year during hottest month of the year. Soil solarisation is an environment friendly soil pathogen management method and practiced widely in north India.

Soil Solarisation

Soil solarisation is an environment friendly method of using solar thermal power for controlling pests such as soil borne plant pathogens including fungi, bacteria, nematodes, and insect and mite pests along with weed seeds and seedlings in the moist soil by mulching the soil usually with a transparent polyethylene cover, to trap solar energy in greenhouses. It may also be described as a method of decontaminating soil or soil disinfestation using sunlight or solar thermal power. This energy/temperature causes desirable physical, chemical, and biological changes in the soil.

Planning

A greenhouse, is basically the purpose of providing and maintaining a growing environment that will result in optimum production at maximum yield. The agriculture in the controlled environment is possible in all the regions irrespective of climate and weather. It is an enclosing structure for growing plants, greenhouse must admit the visible light portion of solar radiation for the plant photosynthesis and, therefore, must be transparent. At the same time, to protect the plants, a greenhouse must be ventilated or cooled during the day because of the heat load from the radiation. The structure must also be heated or insulated during cold nights. A greenhouse acts as a barrier between the plant production areas and the external or the general environment.

Site selection and orientation

A greenhouse is designed to withstand local wind, snow and crop loads for a specific cropping activity. In this way, the structure becomes location and crop specific. The building site should be as level as possible to reduce the cost of grading, and the site should be well aerated and should receive good solar radiation. Provision of a drainage system is always possible. It is also advisable to select a site with a natural windbreak. In regions where snow is expected, trees should be 30.5 m away in order to keep drifts back from the greenhouses. To prevent shadows on the crop, trees located on the east, south, or west sides should be at a distance of 2.5 times their height.

Greenhouses should provide a controlled environment for plant production with sufficient sunlight, temperature and humidity. Greenhouses need exposure to maximum light, particularly in the morning hours. Consider the location of existing trees and buildings when choosing your greenhouse site. Water, fuel and electricity make environmental controls possible that are essential for favourable results. For this reason, use reliable heating, cooling and ventilation.

The greenhouse temperature requirements depend upon which plants are to be grown. Most plants require day temperatures of 70 to 80 degrees F, with night temperatures somewhat lower. Relative humidity may also require some control, depending on the plants cultured. Some plants grow best in cool greenhouses with night temperatures of 50 degrees F after they are transplanted from the seeding tray. These plants include azalea, daisy, carnation, aster, beet, calendula, camellia, carrot, cineraria, cyclamen, cymbidium orchid, lettuce, pansy, parsley, primrose, radish, snapdragon, sweet pea and many bedding plants. Some plants grow best in warm greenhouses with night temperatures of 65 degrees F. These plants include rose, tomato, poinsettia, lily, hyacinth, cattleya orchid, gloxinia, geranium, gardenia, daffodil, chrysanthemum, coleus, Christmas cactus, calla, caladium, begonia, African violet, amaryllis and tulip. Tropical plants usually grow best in high humidity with night temperatures of 70 degrees F.

The variety of greenhouses and greenhouse material, equipment and accessories are so many. However, there are certain basic materials that essential in almost all types of green houses. These are

Structural framing materials

Such materialsinclude low maintenance non-heat conducting timber; strong and durable galvanized steel; or light, low-maintenance and sturdy aluminium alloys. Though plastic pipe frames are usable, they are not very strong to withstand snow load or strong wind sheering forces. What one should choose as the framing material would be determined by the material one wishes to use as glazing, his budget and the permanence of the structure one desires. Aluminium is a popular material for greenhouse framework because it is relatively lightweight, rustproof, affordable and easy to assemble. The downside is that it is not a good insulating material and in very cold weather, heat loss from the metal frame could inflate your heating bill. Also, you would need to look for sturdy frames if your greenhouse is located in an area that experiences high winds. Condensation could also occur on an aluminium frame. Wooden structural frameworks for garden greenhouses are also a popular choice for its aesthetic value, natural feel and the ’warmth’ it exudes. It is an easy material to work with especially if you are not using a greenhouse kit for building. Some greenhouse owners would settle for nothing else as they believe it is the only material that complements the natural beauty of plants inside the greenhouse! Wood is a good insulating material so it will not allow heat loss in cold weather. Reinforced wood has superior strength and has an excellent load bearing capacity. Being a natural material, it has the potential to develop mildew or disease and offer a haven to tiny pests. So, when you choose wood to build the framework of your greenhouse, be sure that you pick a high quality hardy wood such as redwood, cypress or cedar. Also, treat wood with non-hazardous chemicals so that your plants are not adversely affected. The preservatives used for wooden greenhouse frames should be pressure treated, salt type or copper naphthenate. Copper naphthenate is a general use preservative used for pressure treating utility poles and timber. It is known to be very effective in preventing mould, mildew and dry rot. It works very well against wood-damaging fungi and insect pests. Pentachlorophenol is a restricted use wood preservative and is toxic to plants and humans. It is not available to the general public and poles or timber treated with it are not suitable for use in a greenhouse. PVC pipe can also be used as support for small greenhouses that are to be covered with polyethylene, but PVC requires additional support to withstand strong winds. Being flexible, PVC can be used particularly well in hoop houses. Though it has the advantage of offering insulation and, if UV treated, are long-lasting, they are not good at bearing the load of hanging baskets and shelving to any appreciable degree. PVC that is treated to be resistant to ultraviolet radiation is also known as UPVC.

There are different types of greenhouses, the low cost and high cost or low technology or high technology greenhouses. The cost of greenhouse and expenditure on crop production under these greenhouses would vary according to technology to be used and the crop is to be produced. The cost would vary from place to place with location of greenhouse. For each type of greenhouse its cost would vary according to geo-climate, the production practices and input expenditure/availability. The cost of construction of greenhouse in 2019 hence varies from Rupees 500 to 6000 per square meter.

The modern or climate controlled greenhouse requires massive inputs of energy and cost of claddings to grow crops out of season making them high cost structures. However, growing of certain horticulture crops and their nurseries out of season is happening in a sustainable way, using the heat from the sun and soil too. These are called passive solar greenhouses designed to retain as much warmth as possible. This concept has revolutionized vegetable production in Ladakh, high altitudes and other parts of the country in winter months.

The solar greenhouse is especially successful in China and are contributing mainly in vegetable production. Solar passive greenhouses are designed in different shape size using different local and other materials keeping in view the local climate and terrain. The poly houses mentioned earlier such as, low cost polyhoses, Ladakhi poly house, solar trench, polyench are passive solar green houses. Being the opposite of the climate controlled greenhouse, the passive solar greenhouse is heated all-year round with solar energy alone, even when the outdoor temperature drops below freezing point. The indoor temperature of the structure can be higher than the outdoor temperature. The temperature can be around 25°C (45°F).

Such greenhouses have been experimented by Defence Research and Development Organization through its establishment FRL (Field Research Laboratory) now DIHAR (Defence Institute of High Altitude Research), Leh/ Ladakh since 1962 during November to the end of March, the period during which the outside temperature drops there below freezing. The average temperature in the coldest month is between -15°C and -18°C. Over the several decades of research different and effective designs of such greenhouses have been standardized which are suitable to produce fresh vegetables like most of the leafy vegetables, tomato, cole crops and potato at sub zero temperature.

There are several systems for greenhouse heating based on heat source and purpose or crops to be produced in greenhouse.

Electric heaters

Unit space heaters, either floor mounted or supported, are normally dependent on electricity supply supported by stand-by generators. Abroad they are fuelled with natural or bottled gas or fuel oil and use fans for heat distribution. This system requires a relatively moderate capital investment, is easy to install, and provides for easy expansion of facilities. If unit air heaters are used, they should be spaced and directed to blanket the entire area with heated air.

Hot Water Systems

Hot water systems utilize metal pipes that can be perimeter, under benches, or overhead fan forced unit heaters can be used. This system requires a boiler, valves, and other necessary controls. Hot water system is simpler to install and normally requires less maintenance than a steam system. Hot water systems are mainly used in smaller greenhouse.

About 80% of the world population live in developing countries and are dependent on agriculture. Agricultural products, just after harvesting, are dried to the safe moisture level. Open solar drying for drying agricultural products is being practiced since ages throughout the world. Due to its several drawbacks as danger of (dust, rain, ultra-violet rays, birds, animals etc.), advance technique, i.e. greenhouse drying, is being adopted for drying crops to reduce the drying time and increase the quality of the food products.

Drying involves a heat and mass transfer phenomenon in which heat energy supplied to the product surface is utilized in two ways: (i) to increase the product surface temperature in the form of sensible heat and (ii) to vaporize the moisture present in product through the provision of the latent heat of vaporization. The removal of moisture from the interior of the product takes place due to induced vapour pressure difference between the product and surrounding medium. The moisture from the interior diffuses to the product surface to replenish the evaporated surrounding moisture.

The working principle of greenhouse drying is in which the product is placed in trays receiving the solar radiations through the plastic cover and moisture is removed by natural convection or forced convection.

Greenhouse drying are being adopted to reduce the losses and to increase the quality of the dried products. Solar energy is the most promising power source of energy for drying of agricultural products. Most of the farmers adopt open sun drying because it is abundant and inexpensive. But the open sun dried products are also subjected to remarkable losses due to environment. Losses of fruits and vegetables are estimated to be 30%-40% during drying under open sunlight. The post-harvest losses can be reduced by adopting advanced means of drying, i.e. greenhouse drying. The greenhouse dryer can be operated in natural and forced mode as required. Studies reveal that the greenhouse dried products are of superior quality and better colour retention as compared to open sun drying.

The following various types of irrigation methods and their systems are used in crop production in greenhouses and plant nurseries.

1.Hand Watering

2.Perimeter Watering System

3.Tube Watering System

4.Drip Irrigation System

5.Overhead Spray System

6.Ebb and Flow System.

Drainage is the natural or artificial removal of excess water from a surface or sub-surface from an area or field or soil or greenhouse. The internal drainage of most agricultural soils in greenhouse is good enough to prevent severe waterlogging. Water logging creates anaerobic conditions that harm root growth in absence of oxygen. Soils need artificial drainage to improve production or to manage water supplies in certain conditions. Though the roots need moisture but they need oxygen too and poor drainage is g result in roots rotting and death of plants.

The irrigation water inside the greenhouse may accumulate and cause anaerobic condition. Similarly plants in pots should not accumulate water. Water should not stand in pots and beds for longer period. If it stays longer drainage is poor and needs to be corrected. It is better to have good drainage system in greenhouses or protected structures.

Besides irrigation rains water seeps in the greenhouse. The drainage system prevents running or its accumulation in low lying portion of the greenhouse. Drainage system in greenhouses is a must for avoiding damage to the crops.

Flooding

Flooding affects both above and below ground ecosystem processes in greenhouses. Below-ground changes may be less obvious, they are as important as the above-ground changes. Soil microorganisms are sensitive to disturbance, and shifts in soil microbial community structure are expected when anaerobic conditions develop from flooding. The useful aerobic microbes are destroyed by flooding. It takes time to built-up their population in the soil to benefit plants. Due to anaerobic condition created by flooding in greenhouse plant roots in soil are not able to breath, function and hence wilting of plants occurs. Flood irrigation in excess create flood like condition in greenhouses at time. Excess water in soils is a major factor affecting plant survival and functioning. In saturated soils, the supply of atmospheric oxygen into the soil is curtailed and various facultative and obligate anaerobic microorganisms use oxidized compounds as electron acceptors for respiration, thus converting them to reduced forms. The reduction and the associated processes influence plant survival, growth and functioning in wetlands. Flood irrigation should always be just wet the soil not flood inviting stagnation of water.

A chain of reactions is initiated upon soil flooding leading to reduced soil redox potential conditions. These reactions include physical, chemical and biological processes that have significant implications on plants growth. Physical processes include restriction of atmospheric gas diffusion in the soil leading to depletion of soil oxygen and accumulation of carbon dioxide. Shortly after flooding, the limited supply of oxygen in soil pore spaces is depleted rapidly by roots, microorganisms, and soil reductants. This process leads to oxygen depletion and reduction in soil oxidation reduction potential followed by a chain of soil chemical changes. The processes that follow include denitrification, reduction of iron, manganese and sulphate, and changing soil pH

Pasteurization: The heat treatment given to soil to free it of harmful microorganisms or pathogens and pests is called pasteurization. It kills weed seeds also.

Pasteurization of greenhouse plant growing media

Greenhouse growing medium may contain harmful pests such as disease causing organisms, nematodes, insects and weed seeds. It is advisable to decontaminate it by heat treatment or by treating with volatile permissible chemicals.

Soilless media or culture

Gravel culture is a general term which applies to the growing of plants without soil in an inert medium into which nutrient solutions are usually pumped automatically at regular intervals. Haydite (shale and clay fused at high temperatures), soft- or hard-coal cinders, limestone chips, calcareous gravel, silica gravel, crushed granite and other inert and slowly decomposing materials are included in the term “gravel”. The more important greenhouse flowering crops include roses, carnations, chrysanthemums, gardenias, snapdragons, lilies, asters, pansies, annual chrysanthemums, dahlias, bachelor buttons and others.

Media ingredients and Mix

Commercially available materials like peat, sphagnum moss, vermiculite, perlite and locally available materials like sand, red soil, common manure/ compost and rice husk can be used in different proportions to grow greenhouse crops. These ingredients should be of high quality to prepare a good mix. They should be free from undesirable toxic elements like nickel, chromium, cadmium, lead etc. Most common medium other than soil used in India in greenhouses is coco peat. In other countries these are Rockwool and Peat-vermiculite.

Nutrient film technique popularly known as NFT is one of the methods of soilless farming or hydroponics where in plants have their roots in a shallow stream of recirculating water containing all the nutrients required for plant growth dissolved without any solid growing medium. The lower portion of roots remain submerged in flowing nutrient medium in a water tight gully having enough air for the roots. The nutrient film technique was developed during the late 1960s by Dr Allan Cooper at the Glasshouse Crop Research Institute, England. The method is already used in commercial horticulture in many countries including India. NFT is potential for other crops such as animal fodder and even energy-source plants for fuel production.

NFT related technologies

Hydroponics : Cultivation of plants in nutrient solutions is known as hydroponic cutlivation. This ia gerally done under protected structures and in containers arranged horizontally or vrtically (vertical garden). Use of nutrient film or fertilizers is made to feed the plants. Hydroponics can be practiced following nutrient film technique method, trough method, deep water floating method and coco peat bag culture.

The popularity of greenhouse-grown produce continues to rise as it provides a variety of produce during the “off” season. Greenhouses are good for healthy plant nursery production and other a number of crops for profit. Though the greenhouse farming in India like in other countries is progressing but there are certain problems and constraints as stated below.

1.Greenhouse production generally is highly technical and requires constant and continuous attention during cropping period. Relevant information about the crop environmental requirement such as right temperature, humidity etc is essential.

2.Knowledge about the right type of inputs for greenhouse production is a must which is not easily available.

3.Greenhouses cultivation increases the land, water and fertilizer productivity along with reduction in pesticide use. But such interventions are associated with very high initial cost. Although, it is linked with several Government Schemes in India and have 50-90% of subsidies depending on intervention, status / socio-economic condition and policy of State and Central Government.

4.Uninterrupted and regular power supply is required for operating cooling and heating system of the controlled environment greenhouses which necessitate a back-up power pack which is also expensive and underutilized.

Greenhouse technology development has made good progress in India during the last two decades, and steps necessary for promoting greenhouse cultivation of flower and vegetable crops have been started. Energy-efficient greenhouse cultivation continues to be an area of active research and development, and this is sought to be achieved through precision equipment and protocols. While the gap between the demand and supply of most horticultural crops remains wide and the country plans to double the production of horticultural crops by 2012, the protected cultivation technology holds the key to meet the targets. It clearly emerges that greenhouse technology has multipurpose application for sustainable development of a hilly zone. During harsh winter which otherwise threatens the survival of human beings in these remote hilly areas, popularization and further improvements in greenhouse management could provide a sign of relief in solitude of white snow cover.

Abstract

Demand for horticultural commodities is increasing over a period of time. There is increasing pressure on available land for growing of such crops. The production of quality fruits, vegetables and other horticultural crops can be enhanced either by increasing productivity, use of improved cultivars/hybrids and effective production system, bringing additional land under horticultural crops or by promotion of protected cultivation which supports production in adverse climatic conditions and off seasons. Among horticultural crops, production of vegetables, flowers, medicinal and aromatic plants under protected condition is the best alternative to use the land and other resources more efficiently. Greenhouse cultivation is useful and is in practice in all kinds of climatic conditions, may it be severe and extreme cold (Canada and Russia), intolerant summer (Israel, UAE and Kuwait), excessive rains (Phillippines) and in moderate climate in several other countries. Nursery production of crops under protected conditions is highly economically viable.

The area under protected cultivation was only 0.23 per cent of the total area under horticultural crops in India in 2012. To boost up this, a number of varieties are bred for cultivation especially under polyhouse conditions. Greenhouse for vegetable production encompasses glasshouse, polyhouse, insect-proof net house, low tunnel polyhouse and zero energy polyhouse. Protected structures are of different kinds, viz. open-ventilated; closed polyhouse with fan and pad system; shade net house; sloped roof, rain shelter etc. Micro-irrigation has proved its efficacy in saving water, improving the yield and also is responsible for reducing diseases which develop in rather moist conditions. Protected structures appeared as the best means and are being used by many nursery growers for multiplication of healthy planting materials and are becoming popular especially in the hilly regions. Use of techniques like soilless culture, production of high value and low volume flowers and vegetables, hybrid seed of important vegetable crops and grafting of promising varieties on desirable root stocks can be made more efficiently under protected environment. Seed yield of many crops can be 3-4 times more under cover compared to their open field cultivation along with ensured quality.

Protected cultivation technologies in Himalayan high altitudes of India for the welfare of the soldiers and the society are a landmark in cultivation of horticultural crops in non-conventional areas. The protected production system has the potential to contribute greatly for achieving high productivity and stability to production in the present scenario of climate change. Extension of growing/harvesting period including off season is another desirable feature associated with protected cultivation.

Abstract

Limits to crop production are shrinking land area under cropping, shortage and higher cost of irrigation water, fertilizers, pesticides, electricity, labour wages and harvest and post harvest losses due to non-availability of cold chains and storage spaces. Diversification of crops to high value products is yet to gain momentum. Restrictions in marketing due to APMC acts are to be reviewed and drafted farmer-producer friendly. Forcing of horticultural crops-vegetables, fruits, flowers, spices, aromatic crops-to market fresh produces during off season is getting attention and many such units are established as a part of urban and peri-urban horticulture. Ready to assemble forcing structures are now available. Hi-tech nurseries, integrated soil and water management through fertigation, pests and disease management by bio-pesticides, predators and parasitoids, pheromones and light traps are successfully demonstrated. Space saving horticulture focuses on maximization of productivity and minimization of inputs costs in an eco-friendly and sustainable way.

Abstract

Indian Horticultural produce to become competitive both in domestic and international markets, there is an urgent need for use of Hi-tech horticultural technologies. The techniques covered under Hi-tech Horticulture are genetically modified horticulture crop varieties derived from biotechnology and genetic engineering, micro-propagation, protected cultivation, micro irrigation and fertigation, high density planting, organic farming, integrated nutrient, pest and disease management and post harvest management.

Micropropagation or tissue culture technology is based on the principle of totipotency. It provides disease free, uniform sized and year round production of mass multiplication of plants in various stages viz. establishment and stablillization, shoot multiplication, pre-transplant and in vitro rooting and transplanting acclimation and ex vitro rooting. Protected cultivation is the technique of providing to the crop to protect plants from the adverse climate conditions by providing optimum growth and development conditions. High value horticulture crops mainly cut flowers and vegetables are more popular for cultivation in green houses. Greenhouse may be of different types depending on the structural designs followed as quonset, curved roof or gable roof and covering materials used as glass, acrylic, polycarbonate, fiberglass reinforced plastic panels or polyethylene etc. applicators. Micro-irrigation system is used for frequent application of required and measured quantity of water directly above or below soil surface, usually as discrete

drops, continuous drops, tiny streams or miniature spray through emitters or applicators placed along a water delivery line (laterals). It may be in form of drip irrigation, bubbler irrigation, micro jet irrigation, sprinkler, micro-sprinkler or misting (fogger) irrigation system. Similarly under fertigation system, special fertilizers in form of liquid or water soluble solids are available through a suitable irrigation system for accuracy of water application.

Abstract

High Tech interventions begin with acute desire and demand for high productivity and profit from Agricultural activity. High Tech cultivation implies judicious use of space, time and inputs; nothing more and nothing less. It is interesting to note that the different components that were listed in each case above are known to scientists and extension workers and to a lesser extent to farmers also. Piecing them together to formulate a practise is the novel thing. The major components of high tech cultivation assume the highest priority by virtue of the fact that the country has shortage for water and fertilizer and both are essential for any type of crops. Different components of high tech intervention can be used for growing crops, also for the growers to enhance production and quality .High tech intervention includes a number of components like- uniform virus free planting material, drip fertigation technology, assistance to post harvest management, and training and guidance to farmers, value addition opportunity, technical support to the farmers etc. These high tech interventions are introduced to other crops- a host of vegetables, fruits like Pomegranate, Cashew and Guava, and agricultural crops like, Cotton, Pulses, Sugarcane, and even cereals like, maize, wheat and rice. Another important aspect of such interventions is that only if concomitant interventions in marketing of produce are made, the whole exercise would bring profit to the farmers.

Abstract

Protected cultivation of horticultural crops especially vegetables provides the best way to increase the productivity and quality of vegetables especially during off-season, which also fetches better market price. Yield of some of the vegetables like tomato, capsicum and cucurbits can be increased manifold compared to their open field cultivation. Irrigation management is an important aspect of protected cultivation technology for improving the input use efficiency such as water and nutrients for the cultivation of crops under protected environment such as polyhouse, net house, poly tunnels and nursery production. Various other techniques such as use of mulch can be used to further enhance the water and nutrient use efficiency along with improving the quality of produce and precise resource savings. Automation further reduces the manual intervention and increases the input use efficiency.

Abstract

About 20 percent of the world’s total population is residing in the mountains and this proportion is likely to increase in the present century as environmental degradation and pollution are driving the human population for settlement in the clean and serene environment of the mountains. Himalayan region has sizeable area in countries like India, China/Tibet, Nepal, Pakistan, Afghanistan, Bhutan, etc. Remarkable progress has been made in greenhouse research and development in many countries. However, Himalayan regions which reserve unique flora and fauna have attracted little attention so far. Changing climate, fast increasing population and shrinking land and water resources are the major challenges before us to meet the food and nutritional security of the population at global level. Improvement in the production and productivity of crops are the immediate need to boost the availability of food and improve the economic conditions of the farmers.

Greenhouse technology has tremendous potential to improve production and productivity of crops even under uncongenial soil and climatic conditions. The farmers having very small farm holdings in countries like Japan and South Korea have improved their income and living standards by adopting protected cultivation technologies. Similarly, Israel has demonstrated successful crop production under desert and uncongenial climatic conditions by improved water management practices and using greenhouse technology. However, India is yet to trap the potentials of the technology. Modern greenhouses require uninterrupted huge electric power for control of environment (heating/cooling/air circulation etc), which is considered one of the major causes for global warming. High installation and running (energy) cost, high cost of production; poor government support and lack of farmer friendly /cost effective greenhouse technology are some other challenges. Appropriate modifications suiting to our requirements, as per the need of crop, climate and farmers may lead to popularization of greenhouses in the country, especially among the small and marginal farmers. Defence Research & Development Organisation (DRDO) successfully demonstrated the innovative approach to popularize low cost zero energy based solar greenhouse technology in higher Himalayan regions of the country. Such greenhouses are specifically designed using local resources and also trap natural solar radiation/ heat and maintain it for longer period. Similarly, other approaches like using mud/ unbaked bricks, double wall approach, making hot beds, blackening of walls, using water bottles, greenhouse-cum-animal shed, etc. effective to reduce the adverse effects of the environment on crops with little inputs in hilly regions. Need of the hour is to review our approach for the greenhouse technology in farmers’ prospective and device simple and cost effective innovations for fast propagation of greenhouses in the country. This will not only improve the economic status of the farmers but also provide nutritive food to their families and enhance production and productivity of various crops in the country without deteriorating the environment.

Abstract

Keeping in view the increasing demand of off-season and high value vegetables in several big cities of the country, there is an urgent need for diversification from the traditional agriculture by production of high value vegetable crops under different protected conditions for increasing their productivity and quality not only for getting high returns but in a Horti-Business / Veggie-business model. Nursery raising under protected cultivation is highly suitable for such Horti-business model or can be adopted as an agri entrepreneur business in major vegetable growing areas of the country by unemployed youths who are graduates in agriculture or post graduates in horticulture. Low cost protected technologies like plastic low tunnels or walk in tunnels, shade net houses can be used for off season vegetable cultivation for getting high returns. Similarly, insect proof net houses can be used on a large scale for safe vegetable cultivation by way of minimizing the use of pesticides in vegetable cultivation and virus free quality seed production in large number of vegetables in a horti-business model. Some of the technologies like low pressure drip irrigation and low cost nursery raising technology can also be replicated in other parts of the country even among the resource poor and tribal farmers.

Abstract

Space, water and labour have become limiting factors in vegetable production. Moreover, production of off-season vegetables during period of demand fetches better returns. Vegetable forcing for year round production has become a necessity in urban and peri-urban olericulture. With use of pesticides, fungicides, weedicides and chemical fertilizers, health hazards have become visible. Being treated as a field crop, vegetables are exposed to vagaries of weather and floods and droughts take heavy toll. Research on protected cultivation in India is limited but for attempts by private seed companies and enterprising farmers in Karnataka, Maharashtra, Haryana and Punjab. More emphasis is given to tomato, cucumber, capsicum, lettuce and beans. Breeding for varieties suited for protected cultivation is a recent innovation in public sector laboratories. Now there are parthenocarpic cucumbers, tomatoes and capsicum especially to suit protected cultivation. The first four vegetable varieties were developed and released by Uttarakhand State Varieties Release Committee for Horticultural Crops during 2011. These varieties namely Pant Polyhouse Hybrid Tomato -1 , Pant Polyhouse Tomato -2 in tomato and Pant Parthenocarpic cucumber -2 and Pant Parthenocarpic Cucumber -3 in cucumber. These varieties were delivered to ployhouse farmers cross the country.

Abstract

Vegetables are health capsules, being the chief source of vitamins and minerals besides providing other dietary elements like carbohydrates, proteins and even fat and enzymes to some extent, antioxidants and fibre. Though India is the second largest vegetable producer (147 million tones in 2012) in the world, per capita supply and consumption of vegetables in India is very low (160 g day ^-1). It is now realized that the problems of satisfying hunger and nutrition are much beyond the realm of food crops alone and therefore, to supplement and balance our diet, more vegetables are to be included. Vegetables not only provide nutritional security in rural areas but also financial security to small and marginal land holders growing vegetables in the hinterlands of urban markets. Commercialization of vegetable production is the scene of the day as they are money spinners in domestic markets and dollar earners in global markets. To compete in the domestic and global market and for year round supply of quality produce, protected or greenhouse cultivation of vegetables is imperative. Water and nutrients are the top most growth and production inputs in any crop cultivation and vegetables are no exception to this. In order to get the potential yields with matching quality of vegetables grown under protected cultivation, the best of the management strategies to supply water and nutrients is needed. In this direction, drip fertigation is the best option for efficient supply of irrigation water and fertilizer nutrients for greenhouse grown vegetable crops. The studies carried in different parts of the world have clearly indicated that fertigation technology resulted in substantial yield increase with marked enhancement of water and nutrient productivity.

Abstract

High altitudes may be cold and humid or cold or arid ones making the requirements of protected cultivation entirely different in both the conditions. The present chapter is based on the environmental conditions existing in Leh region. Near sub-zero temperature with snow in higher altitudes makes vegetable production tough without use of techniques of protected cultivation. Protected cultivation has witnessed gradual developments from riverbed cultivation practices to use of several types of plastics (PP, PE, PVC etc.) and UV stabilized polythene sheets. Area under protected cultivation is spread worldwide mainly in countries like Holland, Spain, Isaral, China , Japan etc. Protected cultivation technology provides favorable climate for production of vegetable &/or their seedlings of superior quality even in the extreme adverse climate outside. Such structure exploits solar thermal energy to improve photosynthetic efficiency of the plants grown inside. This green house effect is very helpful in winters at high altitudes. Similarly, some modifications in these structures are needed to low the temperature during summers. A number of advantages with some limitations can be listed that are associated with the protected cultivation. At high altitudes, three methods viz. Polyhouse/Greenhouse /Net /shaded house, Low tunnels or row covers and plastic mulching can be used. Polyhouse is a framed structure with 200 micron UV stabilized low density cladding forming a greenhouse effect. Underground trench type polyhouse can also be made with polyethylene supported on wooden poles or GI pipes. Though a combination of above two known as polyench was found performing better in Ladhak area. Low tunnels or row cover use transparent plastic films or net over low hoops to cover rows of plants. Mulching is covering the soil around plants to conserve soil moisture, temperature, preventing weeds etc. using transparent and black plastics of 10-25micron thickness. Double colored plastic mulches are being tested for different crops and different seasons. In arid high altitudes, DRDO (through DIHAR, Leh) has worked extensively on protected cultivation and developed production technologies in the service of nation. Its contribution includes making possible the production of nursery, cucurbits and several other vegetables and their seeds in sub zero climatic conditions. Now, there is a need to develop more area specific, more appropriate, efficient and economic protection structures. Simultaneous development of tools, machinery and vegetable varieties suitable for use in protected conditions are among the major aspects of future work to be done in this field.

Abstract

Production of healthy and vigorous seedlings is the foremost crucial step for raising a successful vegetable crop. Now a days seedlings are raised in trays under controlled atmospheric conditions called as transplants. As soil substitutes, artificial media made of perlite, vermiculite and peat moss are commercially available. A good rooting medium should be light weight, well drained, well aerated, and soilless with or without starter solution or added nutrients and with good water and nutrient holding capacity. The media should be sterilized before use. Selection of trays for cell shape, size and number depends on the type and nature of crop. Most of the vegetable transplants are now being produced in hardened plastic or polystyrene containers. Only good quality certified seeds should be used in media filled trays after priming, pelleting, coating or other seed treatments as per the crop requirement. Germination chambers as insulated rooms to maintain suitable conditions over large period of time may also be used. Generally vegetable crops need fertilizer application after expansion of first true leaf. Young seedlings are managed carefully to avoid any toxicity while taking care of their nutrient management. Water requirement also depends on growth stage and variation in weather conditions. Other seedling management practices include shading, thinning, weeding, disease/pest control, hardening off and subsequent transplanting. Containerized greenhouse plants can be grown using the conventional “rail” (or rack) system or the “float” system. Shipping factors such as mechanical injury, environmental conditions and length of storage affect plant vigour and establishments. IPM (integrated pest management) offers a practical way to effectively manage pests on vegetable bedding and transplants.

Abstract

Greenhouse vegetable cultivation is gaining popularity for reasons such as high productivity of quality produce round the year with enhanced input use efficiency. As agriculture has a major share in our economy and if India has to emerge as an economic power in the world, the productivity should substantially increase from the present levels. We need a new and effective technology which can constantly improve the productivity, profitability and sustainability of our major farming systems. One such technology is the green house vegetable production technology. At Indian Institute of Horticultural Research, Bangaluru, research on greenhouse vegetable production is in progress since the year 2000, resulting in the development of many technologies which have made possible to realize high yield levels in tomato, capsicum and cucurbits that are comparable to international standards of greenhouse productivity. Tomato and bell pepper yields have touched 300 tonnes and 200tonnes/ha/year, respectively and cucurbits 80 to 100 tonnes/ha/crop of 3 months. Vegetable cultivation in cost effective greenhouse is a technical reality in India, which is being adopted by resourceful farmers in and around big towns and cities as a peri-urban horticultural system. Such production systems have not only extended the growing season of vegetables and made their availability round the year but also opened the possibilities of growing new vegetables such as coloured capsicums, cherry tomatoes, seedless watermelons, icebox melons, sweet cucumbers, coloured cabbage, etc., besides tomato, cucumber, eggplant and climbing beans. Quality seedling production is one more important greenhouse activity in the present agricultural scenario as more and more F₁ hybrids are being adopted by the farmers.

Protected cultivation is a specialized agricultural system in which a certain control of the soil–climate ecosystem is exercised modifying its conditions (soil, temperature, solar radiation, wind, humidity and air composition). Plants are cultivated by means of these techniques modifying their natural environment to prolong the harvesting period, alter the conventional cropping cycles, increase yields, improve product quality, stabilize production and provide products when open field cultivation is limited (Wittwer and Castilla, 1995). It is the most contemporary approach to produce mainly, horticultural crops qualitatively and quantitatively and has spread extensively the world over in the last few decades. Protected cultivation also known as controlled environment agriculture (CEA) is highly productive, conservative of water and land and also protective of the environment (Jensen, 2002). Protected cultivation is now becoming popular in Kerala experiencing humid tropical climate with the adoption of locally suitable green house technologies.

Protected cultivation has rapidly expanded in many regions across the globe as early as 1960, when plastics were introduced/used in agriculture and subsequently during 1970’s, when the rise in oil prices resulted in increase of energy costs. About 115 countries in the world are into greenhouse vegetable production commercially (Sabir and Singh, 2013). The world scenario shows the area under protected cultivation to be nearly 6,23,302 ha. while total estimated world greenhouse vegetable production area is 4,02,981 ha. Of the total world greenhouse vegetable area, soilless/hydroponic culture systems account for 95,000 ha (Hickman, 2011).

The advent of protected cultivation technology in India materialized during the early nineties, post globalization. In India, area under protected cultivation is presently around 25,000 ha while the greenhouse vegetable cultivation area is about 2,000 ha. Faced with constraints of land holdings, rapid urbanization, declining crop production, declining biodiversity and ever increasing population, demand for food, especially vegetables has increased manifold and protected cultivation has offered a new dimension to produce more in a limited area. Today Dutch protected cultivation is one of the most intensive farming systems in the world with high levels of output by using the latest technologies (Goncharova, 2004).

Abstract

Protected cultivation technology in black pepper and cardamom offers distinct advantages over conventional farming. Production of quality planting materials irrespective of the season was made possible. Such propagating materials can be well maintained under polyhouse, irrespective of the seasons and can be used judiciously for replanting/ gap filling. In this era of climate change, protected cultivation assumes significance. In black pepper and cardamom, rapid multiplication techniques of planting materials were made possible. A novel idea of growing pepper, different from conventional system as “bush” that can be grown under potted and field conditions were also developed. Nutrition and water management studies could be undertaken with precision. In cardamom, quality planting material production and high quality capsule production are made possible all throughout the year by the adoption of protected cultivation. For optimizing production, prescriptions of fertilizers, using DRIS norms were developed for black pepper and cardamom based on critical soil and foliar nutrient concentrations. Typical deficiency symptoms of major and micro nutrients on black pepper were characterized to rectify the deficiency. Technology for propagation and cultivation of bush pepper in pots, under protected cultivation was also developed and popularized. Technology for using organic manures, non edible oil cakes, biofertilizers towards production of high quality zero defect black pepper and cardamom was also developed and popularized.

Abstract

Floriculture is the fast emerging sector in horticulture sector and people are changing very fast from the traditional field crops to flowers because of high returns per unit of area and better price. The flowers are being used during all the occasions. Though the art of growing flowers is not new to India, large scale commercial cultivation and protected cultivation in polyhouses is relatively new in India. With the opening up of world market in the WTO regime, there is a free movement of floriculture products worldwide. India is having a better scope in future as there is a shift in trend towards tropical flowers and this can be gainfully exploited by countries like India with high amount of diversity in indigenous flora. The major flowers grown under protected cultivation are rose, chrysanthemum, gerbera, carnation and lilium. Even some of the flowers are location specific and made a dent on the state economy, the best examples are carnation in Himachal Pradesh and gerbera in Maharashtra. Now with market trend is changing and biotechnological tools must be exploited for the crop improvement to evolve novel varieties with desirable colour traits. The other major area of work is on protected cultivation of cut flowers which is coming up on a large scale and value addition in floriculture i.e. extraction of pigments, essential oils, pharmaceutical and nutraceutical compounds have emerged as frontline avenues in floriculture. We have many challenges ahead like trained HRD, quality planting material, technical knowhow, limited choice of the varieties and products in the market to compete in global market.

Abstract

Domestic market both for cut flowers as well as loose flowers have increased significantly owing to rapid urbanization, changes in social attitude, increase in income level and the increasing habit of ‘saying it with flowers’. The per capita consumption of flowers is increasingly growing up due to which the production has been increased and non-traditional areas have emerged as important players in floricultural production. In this scenario of intensive production system, protected cultivation can be a viable option. Protected cultivation offers unique opportunities to produce high quality flowers round the year and insulate from weather vagaries thus, reduceing risk from the climatic variations. Protected structure comprises of high cost, medium cost and low cost polyhouses and each structure needs specific varieties and technologies to achieve maximum yield. Hence, breeding program should be based on structure and climate as it has been observed that varieties bred in Northern hemisphere under high cost greenhouses are not performing alike in medium and low cost polyhouses of Southern hemisphere. Breeding work in India has been carried out in wide range of floriculture crops. Breeding of many floricultural crops are in fact not always simple and straightforward due to polyploidy, complex ancestry involving one or more species, aneuploidy, and in some families self and cross sterility barriers, etc. It appears that breeders have vast opportunities to incorporate disease and insect screening and development of varieties for protected cultivation in routine breeding programs during the evaluation of seedlings. To develop varieties for such adversities, our research institutes should have enough infrastructures to carry out required research. In a few areas, protected cultivation has succeeded in India due to efforts of private companies and enterprising farmers. Recently, with greater efforts of ICAR a few public institutions have started breeding of flower varieties suited for protected cultivation.

Abstract

The tradition of growing of flowers is age old. The flowers have travelled from the bowl of prayers to gardens to commercial sector for revenue. The quality concerned world demands for round the year production and supply of quality produce which can only be possible under controlled environment production. A range of location specific and crop specific infrastructures are being commercially used for production of planting material and flowers. General and crop specific guidelines for trade of cut flowers are available which the producers and policy makers must know for successful promotion of export of cut flowers from the country. The producer can also use practical methods for vase life study of their produce which is of great relevance in cut flower trade.

Keywords: Protected floriculture, trade, crop specific guidelines, export, cut flower

Introduction

Indian floriculture industry is shifting from traditional flowers to cut flowers for export purpose. The liberalized economy has given an impetus to Indian entrepreneurs for establishing export oriented units (EOUs) under controlled climatic conditions. The wide variations in agro climatic conditions in India permit us to grow various types of tropical and subtropical flowers. Though such plants grow successfully in open conditions without cover, they fail to meet the quality requirements of being blemish free. High quality ornamental plants meant for export should be scientifically grown only in plastic, glass or fibre glass greenhouses or at least under partial cover. Though initial investment is high in protected cultivation, the products in them will obtain far more attractive prices.

Even though we are now in the atomic age, the idea of the atom is not new. More than 2,000 years ago, the Greek philosopher Democritus suggested that any matter is composed of tiny indestructible particles called Atoms. The word atom is derived from the Greek word Atoms meaning something that can not be cut further. However not much attention was paid to this concept till 1808, when Dalton proposed the famous “Atomic theory”. According to this theory, “all matter is composed of tiny indivisible particles called ‘Atom’. Combining the ideas of Lavoisier, Boyle and his own, Dalton proposed that atoms of elements combine together to make molecules of a compound. This was a great step in the concept of the atom and compounds, since this gave a clear picture of how the supposedly smallest particles of matter called atoms could be put together to form the various familiar substances found in nature.

2.1 Isotopes

In 1913, J.J. Thomson and Aston introduced atmospheric neon into the positive ray apparatus and got two parabolas corresponding to masses 20 and 22, with the intensities of the tracks corresponding to the ratio of 9:1, irrespective of the condition of discharge and pressure. This indicated that neon existed in two forms having atomic weights 20 and 22, and at the same time it could not be distinguished chemically. These two types are known as isotopes of neon (iso = same, topas = place in the periodic table). When the average atomic weight of the ordinary neon was calculated based on the abundance of these two forms in the ordinary neon, it was found to be 20.2 which agreed the chemical methods. Thus the existence of isotopes of a given element was discovered.

Formerly isotopes were defined chemical properties but with different atomic weights, the same atomic number and occupying the same position in the periodic classification. Later this definition was slightly modified and now isotopes are defined as nuclides with the same number of protons but differing in the number of neutrons, for example, ordinary hydrogen (also called protium ; proton =1 and neutron =0), deuterium (heavy hydrogen ; proton =1 and neutron = 1), and tritum super heavy hydrogen (proton =1 and neutron =2). Investigations using mass spectrographs have revealed more than 280 isotopes which are stable artificially radioactive isotopes.

Radioactivity

The discovery of radioactivity, in general, actually came about on a few different fonts. First was the discovery of x-ray radiation that was artificially generated in a laboratory, followed by the discovery of several elements that naturally emit radiation when the nucleus of the atoms disintegrates or decay. These are the elements that today are called radioactive elements and are said to have unstable nuclei.

4.1 Selection of Isotopes for Tracer Studies

In radioisotopes we have all the essentials of a powerful research tool, a non-destructive means by which atoms could be followed and detected in the organism. Application mainly depends on the fact that chemical properties of the isotope of an element are essentially identical.

The basic requirement of a tracer is that it be

1.Chemically and physically, virtually equivalent to the substance it represents or displaces and that it, in no appreciable way, affect the system differing from its normal counterpart.

2.Radioactivity could be detected directly and

3.Unaffected by the physical or chemical treatments that are given. Hence, this has been used widely in the investigations of the various problems in biology, chemistry, physics and other fields like agriculture.

Carbon dating uses the half-life of Carbon-14 to find the approximate age of an object that is 40,000 years old or younger.

5.1 What is radiocarbon dating ?

Radiocarbon dating is a method of estimating the age of organic material. It was developed right after World War II by Willard F. Libby and coworkers, and it has provided a way to determine the ages of different materials in archeology, geology, geophysics, and other branches of science. Some examples of the types of material that radiocarbon can determine the ages are wood, charcoal, marine and freshwater shell, bone and antler, and peat and organic-bearing sediments. Age determinations can also be obtained from carbonate deposits such as calcite, dissolved carbon dioxide, and carbonates in ocean, lake, and groundwater sources.

Although a number of radioactive isotopes are found in nature, most of the isotopes used as radioactive tracers are produced artificially. Methods for producing radioactive isotopes include nuclear fission and the bombardment of selected materials by neutrons or positively charged particles.

6.1 Production of Radioactive Nuclides

Nuclear Reactors

In a nuclear reactor, a fissionable nuclear fuel such as ²³⁵U or ²³⁹Pu is placed in a defined geometry within the reactor core. Fast moving neutrons released as the ²³⁵U or ²³⁹Pu nuclei fission are slowed to thermal energy (0.025 eV) by a low-Z moderator such as water, heavy water, beryllium, or graphite surrounding or mixed intimately with the nuclear fuel. The slowly moving neutrons are absorbed by addition of ²³⁵U or ²³⁹Pu nuclei, and a chain reaction is maintained. The rate of absorption of slow neutrons by fissionable nuclei determines the fission rate for the reactor and is controlled by placing inert neutron absorbers in the reactor core. Typical neutron absorbers, usually termed control roads include boron and calcium. Heat generated in the reactor is removed by a coolant such as water or one of a variety of gases or liquid materials.

7.1 Measurement of Radiation Dose

Radiation dosimetry involves the measurement of the energy actually absorbed in a substrate exposed to ionizing radiation. The radiation may be either electromagnetic or corpuscular in nature. The passage of electromagnetic radiation through a substrate causes ionization by virtue of the secondary electrons released. Particle radiations on the other hand, ionize directly because they are charged, or indirectly through the charged particle resulting from a collision with a substrate. Alpha, beta particles, and protons yield primary ionization. Gamma rays and neutrons produce ionizing radiation by their interaction with the substrate in passage through it.

Although some forms of electromagnetic energy, such as light and heat, can be detected by the human senses. One of the greatest draw backs to high energy radiation is the inability to detect it. We cannot see, feel, taste, smell, or hear the various forms of ionizing radiation. Fortunately, ionizing radiation interacts with matter which makes detection and measurement possible by utilizing specialized equipment. In this section we want to introduce you to the various ways and means of detecting and measuring ionizing radiation.

As mentioned previously, Becquerel discovered radioactivity because it left marks on photographic film as a means of detecting radiation. However, there are more definitive means commonly used by scientists and technicians who study and work with radiation. The equipment utilized for the detection and measurement of radiation commonly employs some type of a substance or material that responds to radiation. Many common methods use either an ionization process or molecular excitation process as a basis. Remember that we stated earlier that radiation interacts with matter. For detection and measurement purposes the process of ionization is the most commonly employed technique, based on the principle of charged particles producing ion pairs by direct interaction. These charged particles may collide with electrons, which remove them from their parent atoms, or transfer energy to an electron by interaction of electric fields.

9.1 Potential Tracer Difficulties and their Corrections

In radioactive measurements, the observed counting rate is not equal to the true disintegrations rate of the sample since a number of factors like nature of detectors tend to increase it or, in a majority of cases, decrease the actual counts. Some of the important factors responsible for this are

1.Background,

2.Backscattering

3.Absorption

4.Self absorption

6.Geometry

7.Instrument efficiency

Radionuclides are used in two major ways: for their chemical properties and as sources of radiation.

Radionuclides of familiar elements such as carbon can serve as tracers because they are chemically very similar to the non-radioactive nuclides, so most chemical, biological, and ecological processes treat them in a near identical way. One can then examine the result with a radiation detector, such as a Geiger counter, to determine where the provided atoms ended up. For example, one might culture plants in an environment in which the carbon dioxide contained radioactive carbon; then the parts of the plant that had laid down atmospheric carbon would be radioactive.

In medicine, radioisotopes are used for diagnosis, treatment, and research. Radioactive chemical tracers emitting gamma rays that can provide diagnostic information about a person’s internal anatomy and the functioning of specific organs. This is used in some forms of tomography single emission computed tomography and positron emission tomography scanning. Radioisotopes are also a promising method of treatment in hemopoietic forms of tumors, while the success for treatment of solid tumors has been limited so far. More powerful gamma sources are used to sterilize syringes and other medical equipment. About one in two people in Western countries are likely to experience the benefits of nuclear medicine in their lifetime.

In biochemistry and genetics, radionuclides are used to label molecules and allow tracing chemical and physiological processes occurring in living organisms, such as DNA replication or amino acid transport.