A greenhouse is a framed or an inflated structure covered with a transparent or translucent material in which crops could be grown under the conditions of at least partially controlled environment and which is large enough to permit persons to work within it to carry out cultural operations. The growing of off – season cucumbers under transparent stone for Emperor Tiberius in the 1st century, is the earliest reported protected agriculture. In the 16 th century, glass lanterns, bell jars and hot beds covered with glass were used to protect horticultural crops against cold. In the 17th century, low portable wooden frames covered with an oiled translucent paper were used to warm the plant environment.
In Japan, primitive methods using oil -paper and straw mats to protect crops from the severe natural environment were used as long ago the early 1960s. Greenhouses in France and England during the same century were heated by manure and covered with glass panes. The first greenhouse in the 1700s used glass on one side only as a sloping roof. Later in the century, glass was used on both sides. Glasshouses were used for fruit crops such as melons, grapes, peaches and strawberries, and rarely for vegetable production. Protected agriculture was fully established with the introduction of polyethylene after the World war II. The first use of polyethylene as a greenhouse cover was in 1948.
The total area of glasshouses in the world (1987) was estimated to be 30,000 ha and most of these were found in North- Western Europe. In contrast to glasshouses, more than half of the world area of plastic green houses is in Asia, in which China has the largest area.According to 1999 estimates, an area of 6, 82,050 ha were under plastic greenhouses. In most of the countries, green houses are made of plastic and glass; the majority is plastic.
In general, the percentage of carbon dioxide in the atmosphere is 0.035% (345 ppm). But, due to the emission of pollutants and exhaust gases into the atmosphere, the percentage of carbon dioxide increases which forms a blanket in the outer atmosphere. This causes the entrapping of the reflected solar radiation from the earth surface. Due to this, the atmospheric temperature increases, causing global warming, melting of ice caps and rise in the ocean levels which result in the submergence of coastal lines. This phenomenon of increase in the ambient temperature, due to the formation of the blanket of carbon dioxide is known as greenhouse effect.
Advantages of Greenhouses
Throughout the year four to five crops can be grown in a green house due to availability of required plant environmental conditions. The productivity of the crop is increased considerably. Superior quality produce can be obtained as they are grown under suitably controlled environment. Gadgets for efficient use of various inputs like water, fertilizers, seeds and plant protection chemicals can be well maintained in a green house. Effective control of pests and diseases is possible as the growing area is enclosed. Percentage of germination of seeds is high in greenhouses. The acclimatization of plantlets of tissue culture technique can be carried out in a green house.
Agricultural and horticultural crop production schedules can be planned to take advantage of the market needs. Different types of growing medium like peat mass, vermiculate, rice hulls and compost that are used in intensive agriculture can be effectively utilized in the greenhouse. Export quality produce of international standards can be produced in a green house. When the crops are not grown, drying and related operations of the harvested produce can be taken up utilizing the entrapped heat. Greenhouses are suitable for automation of irrigation, application of other inputs and environmental controls by using computers and artificial intelligence techniques. Self-employment for educated youth.
