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I. Greenhouse vegetable farming:
Greenhouse vegetable farming is a highly controlled form of agriculture based on the production of vegetables under a transparent cover material all year round by creating environmental conditions favorable for plants growth.

II. Greenhouse sustainability:
Greenhouse production is augmenting in response to the population increase, water shortage, climate change and consumer demands for high quality products all the year.
The world population is continuing to grow and our resources are slowly but surely being depleted. In the future we will need double the amount of food that we need now, but it will have to be produced with half of the resources we use now, so we have to be able to do more using less and in a better way.
Vegetables produced in greenhouse are grown sustainably with the greatest care and attention. The grower has the ability to control different factors such as temperature, ventilation, relative humidity, energy and water so that nothing is wasted.
Nowadays crop protection products are hardly ever used in greenhouses. Harmful insects are controlled by releasing predatory mites or predatory wasps to the crops.
All of these sustainable solutions ensure that plants can grow as well as possible with the least possible side effects. More can be produced using the fewer possible resources in such way that the quality of vegetables is improved.

III. Advantages and disadvantages of greenhouse vegetable farming:
1) Advantages:
• Sustainable crop production
• Controlled environment for plant production
• Reduces pesticides and other chemicals use
• Protects plants from adverse environmental conditions
• Protects plants from biotic and abiotic adversity
• Conserves water
• Reduces labor
• Facilitates harvesting
• Allows production of crops all year round
• Increases the yield
• Increases the quality
2) Disadvantages:
• High installation cost
• High maintenance cost
• High technical knowledge
• Requires regular inspection

IV. Principle of greenhouse effect:
The greenhouse effect occurs when the solar radiation particularly the visible light enters the greenhouse through the cover material. Part of this solar radiation is reflected back outside the greenhouse and part of it is absorbed by plants and soil. As a result the temperature inside the greenhouse rises.

V. Greenhouse shapes:
• Even span greenhouse: a greenhouse where both sides of the roof are of equal length
• Uneven span greenhouse: a greenhouse where both sides of the roof are of unequal length, one side of the roof is longer than the other side. The longer side faces south, exploiting the suns heat to the maximum
• Lean-to greenhouse: a greenhouse attached to a building or other greenhouses. The roof slopes to one direction facing south
• Quonset greenhouse (tunnel): a semicircular greenhouse that lacks of height near the side walls
• Gothic arch greenhouse: a greenhouse that has a pointed arch frame resting on side walls
• Round arch greenhouse: a greenhouse that has a rounded arc frame resting on side walls
• Ridge and furrow greenhouse: a series of even span greenhouses connected together
• Sawtooth greenhouse: a greenhouse where multiple lean-to greenhouses are connected together

VI. Greenhouse structure:
1) Frame materials:
Frame materials must be strong with a light weight and must allow even distribution of light to the plants.
• Wood: is easy to construct, has a low installation cost, but it has a limited life duration and it requires high maintenance
• Steel: is durable, resistant to loads, has a low cost but may rust due to oxidation
• Aluminum: is resistant to loads, has a long life duration, does not rust but it is expensive
2) Covering materials:
There are many types of covering materials such as glass, plastic films (polyethylene film, polyvinyl chloride film, ethylvinyl acetate film, polyvinyl fluoride film, polyester film, and ethylene tetrafluoroethylene film) and rigid plastic (rigid polyvinyl chloride, acrylic sheets, methyl polymetracrycil, fiberglass reinforced plastic panels and polycarbonate sheets). A good cover material should be strong, light in weight, transparent with good transmissivity, resistant to heat, to UV, to scratch, to hailstone damage and to weather damage.

VII. Greenhouse location:
• Climate: optimally the greenhouse should be constructed in an area characterized by a high light intensity, a mild temperature in winter, and a moderate atmospheric humidity
• Topography: the greenhouse should be constructed on an area with a gentle slope, this will allow water to drain systematically without any mechanical method
• Soil type: the greenhouse should be installed on a well-drained soil, rich in nutrient and free from insects and diseases
• Wind direction: the greenhouse should be constructed on a site protected from strong winds
• Orientation: the greenhouse should be oriented either toward the east, the southwest or the west
• Water: the greenhouse should be located near a water source, water should be always available
• Accessibility: the greenhouse should be located in a place that is in proximity to markets for easy transportation

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