Green house2/18/2023 ![]() The second structure helps to extend the growing season or permits off-season production by way of controlling light, temperature, humidity, carbon-dioxide level and nature of root medium. The former do not have any environmental control system except for the provision of adequate ventilation and fogger system to prevent basically the damage from weather aberrations and other natural agents. Polyhouse can be divided into two types namely, naturally ventilated polyhouse and environmental controlled polyhouse. The crops grown in open field are exposed to vivid environmental conditions, attack of insects and pests, whereas the polyhouse provides a more stable environment. High rate of return/premium price in the international market for the produce justifies the high investment cost of the green house. This is mostly suitable for producing high value crops with stringent quality standards aimed at international market. To overcome some of the difficulties in medium-tech greenhouse, a hi-tech greenhouse where the entire device, controlling the environment parameters, are supported to function automatically. These greenhouses are suitable for dry and composite climatic zones. As these systems are semi-automatic, hence, require a lot of attention and care, and it is very difficult and cumbersome to maintain uniform environment throughout the cropping period. Evaporative cooling pads and misting arrangements are also made to maintain a favourable humidity inside the greenhouse. Exhaust fans with thermostat are provided to control the temperature. Whole structure is firmly fixed with the ground to withstand the disturbance against wind. The canopy cover is attached with structure with the help of screws. This type of greenhouse is constructed using galvanized iron (GI) pipes. Greenhouse users prefers to have manually or semi-automatic control arrangement owing to minimum investment. Otherwise, inside temperature is increased when all sidewalls are covered with plastic film. Such structure is used as rain shelter for crop cultivation. The temperature can be reduced during summer by opening the sidewalls. Even light intensity can be reduced by incorporating shading materials like nets. Simple techniques are, however, adopted for increasing or decreasing the temperature and humidity. Unlike conventional or hi-tech greenhouses, no specific control device for regulating environmental parameters inside the greenhouse is provided. The ultra violet (UV) film is used as cladding materials. Low cost greenhouse is a simple structure constructed with locally available materials such as bamboo, timber. 6.2.2 Classification of Greenhouse Based on Suitability and Cost Besides, rain water harvesting and favouring short duration crops are also the major advantages of these protected structures which make it suitable for tropical islands. In recent times, however, environmental control can also include cooling to mitigate excessive temperatures, light control either shading or adding supplemental light, carbon dioxide levels, RH, water, plant nutrients and pest control. The primary environmental parameter traditionally controlled is temperature, usually providing heat to overcome extreme cold conditions. In general, greenhouses and other technologies for controlled environment plant production are associated with the off-season production of vegetables, ornamentals and food crops of high value in cold climate areas where outdoor production is not possible. Greenhouse cultivation as well as other modes of controlled environment cultivation has been evolved basically to create favourable micro-climates, which favours crop production all through the year or part of the year as required. Greenhouses are frames of inflated structure covered with a transparent material in which crops are grown under controlled environment conditions. Studies indicated that 40%–45% naturally ventilated polyhouses, rain-shelters, walk-in-tunnels, shadenets and temporary shelters are in common use for vegetable cultivation in the tropics ( Arya et al., 2001). ![]() Protected cultivation in high value vegetable crops can be established even as a small scale industry for major vegetable by progressive farmers or farmer cooperatives especially in periurban areas. ![]() It is possible to grow any plant in any place at any time by erecting a greenhouse/glass house called protected cultivation where the micro-climatic conditions are so modified to suit to the crop needs. Swarnam, in Biodiversity and Climate Change Adaptation in Tropical Islands, 2008 6.2 Protected Structures
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