35 GREEN HOUSE TECHNOLOGY

N. Gayathri

Introduction

Green houses are structures used to start and grow plants year- rounded with walls and roof made by transparent materials such as glass in which plants requiring regulated climatic conditions. The structure of green house range in size from small sheds to large industrial- sized buildings. The purpose of green house is exposed to sunlight becomes significantly warmer than the external ambient temperature and to protect the plants in cold weather. It should be under the environmentally controlled conditions. It should be located to receive the maximum amount of sun-light. Further, green houses control temperatures, moisture, ventilation and climate. Greenhouses allow for greater control over the growing environment of plants. Depending upon the technical specification of a greenhouse, key factors which may be controlled include temperature, levels of light and shade, irrigation, fertilizer application, and atmospheric humidity. Greenhouses may be used to overcome shortcomings in the growing qualities of a piece of land, such as a short growing season or poor light levels, and they can thereby improve food production in marginal environments. As they may enable certain crops to be grown throughout the year, greenhouses are increasingly important in the food supply of high-latitude countries. Greenhouses are often used for growing flowers, vegetables, fruits, and transplants. Special greenhouse varieties of certain crops, such as tomatoes, are generally used for commercial production.

History of Green House

The concept of greenhouses also appeared in Netherlands and then England in the 17th century, along with the plants. There were serious problems with providing adequate and balanced heat in these early greenhouses. Today, the Netherlands has many of the largest greenhouses in the world, some of them so vast that they are able to produce millions of vegetables every year. The plan of growing vegetables and fruits under environmentally controlled conditions has existed since Roman times. The gardeners of Roman used the green house technology of growing cucumbers every day. Cucumbers were planted in wheeled carts and raised in sunny day and then taken to inside of the large space and keep them at night for warm. Initially the temperature of green house was measured manually in 15th century Korea. The Victorian era was the golden period of green house in England, where the largest green houses were conceived and constructed. Greenhouse structures was adapted in 1960 when wider sheets of polyethylene film became widely available. Hoop houses were made by several companies and were also frequently made by the growers themselves. Constructed of aluminum extrusions, special galvanized steel tubing or PVC water pipe, construction costs were greatly reduced. This resulted in many more greenhouses being constructed on smaller farms and garden centers. Polyethylene film durability increased greatly when more effective UV-inhibitors were developed and added in the 1970s; these extended the usable life of the film from one or two years up to 3 and eventually 4 or more years.

Gutter-connected greenhouses became more prevalent in the 1980s and 1990s. These greenhouses have two or more bays connected by a common wall, or row of support posts. Heating inputs were reduced as the ratio of floor area to exterior wall area was increased substantially. Gutter-connected greenhouses are now commonly used both in production and in situations where plants are grown and sold to the public as well. Gutter-connected greenhouses are commonly covered with structured polycarbonate materials, or a double layer of polyethylene film with air blown between to provide increased heating efficiency.

Aims of green house

There are three purposes of green house include:

1.      Provide a controlled environment for plants grown on a large scale.

2.      Grow plants in areas where outdoor growth during winter seasons is not possible.

3.      Extend the growing season for plants that would normally go dormant.

For optimal growth of plants, the temperature in green houses controlled and monitored. Plant growth in a greenhouse also depends upon moisture (humidity). Moisture aids in helping plants maintain their shape and nutrient transport. The amount of water needed by plants depends on the type of plants and the conditions outside the greenhouse. Ventilation or the movement and exchange of air is important for optimum growth. Ventilation helps to ensure the proper temperature and humidity in the greenhouse. When considering greenhouse, the climate of the area must also be considered. The climate will directly influence the structure and the heating and the cooling systems.

Greenhouse cultivation helps to create favorable microclimates where production of vegetables and flowers is made possible throughout the year or part of the year as per the requirement. Greenhouse not only creates suitable environment for the plants but also encourages proper growth and fruiting as compared to open field cultivation. The greenhouse technology has also tremendous scope in horticultural sector, especially for production of hybrid seeds, high value vegetables, ornamental plants, medicinal plants, cut flowers and fruits, which fetch more prices in domestic as well as international markets. Open sun drying (OSD) is the most primitive crop drying, under which the solar radiation falls directly on the crop surface and it is absorbed. The absorbed radiation heats the crop and evaporates the moisture from crop.

Features of greenhouse

Greenhouses can be constructed in different types of materials. They are aluminum, iron, steel, concrete blocks, or wood. Materials used to cover the greenhouse can be glass, soft plastic (polythene, vinyl or polyvinyl fluride), fiber glass, shade fabric, acrylic rigid panels, or poly carbonate rigid panels. Some shapes for greenhouses are detached A- frame truss, Quonser style and ridge furrow. There are also cold frames, hotbeds and lath houses.

Green house management involves a highly specialized and unique area of horticulture, requiring a strong understanding of plant growth and development, crop production, growing media, fertilization, mineral nutrition, water, quantity and quality, growth regulators, and disease and pest management. Green house managers must also have a good understanding of environmental management, heating and cooling systems.

The typical greenhouse available in India was originally designed for farmers in developed countries who grow high value flowers or vegetables – well out of the price range of a low income farmer. The new greenhouse is simpler, with fewer materials and a smaller footprint that is 2% of the land area of a typical farm in India. The layers of shade netting on the top reduce the temperature inside by 5-8 degree Celsius. Insect netting on all sides reduces pest attack by 90%. A profitable harvest, of course, needs more than a greenhouse. A drip irrigation system, coupled with shade that reduces heat and evaporation, helps cut water usage by 90%. They also need access to right seeds and fertilizers to be used inside, and the right training needed to manage any disease. Since a greenhouse can protect crops from floods and pests, the farmers are able to grow seven times more produce. All this goes to show that a greenhouse is a worthwhile investment that can stabilize both environmental conditions and generate income through the year.

Classifications of greenhouses

Greenhouses may be classified based on the following

1.      Covering material

2.      Environmental control

3.      Shape

Types of greenhouse based on covering material

They are,

Glasshouse Plastic house

Shade net house

Glass house

This is the earliest type of greenhouse. Green houses have long life span, are the least affected by weather, noncombustible, resistant to UV radiations and air pollutants. Glass requires regular cleaning to maximum light transmission.

Plastic house

Modern plastics provide an alternative to traditional glass for covering the glasshouse. Plastic glazings include rigid plastic- structured panels like fiberglass reinforced polyester (FRP), Polycarbonate (PC), Polycarbonate(PC), acrylic, polymethyl, methacrylate (PMMA), polyvinyl chloride(PVC) and ethylene vinyl acetate copolymer. These materials are used in single, double and even triple layers to cover the greenhouse.

Shade net house

These are hand woven nets with different light transmission capacity. Shading is often the most suitable procedure to overcome high humidity and temperature or low humidity in the greenhouse or outdoors. Light waves passing through the nets are affected by the shade created by shape and weave of net threads, by net quality and material surface.

Types of greenhouse based on environmental control

• Green houses fall into three categories based on the extent of environmental control
• Fully environmental controlled (high cost) are high-tech greenhouses with all operations computer -controlled .
• Only moderate control is adopted in partially controlled medium cost greenhouses.
• Only  natural  ventilation  is  utilized  in  naturally  ventilated  (low-cost)  greenhouses.

Types of greenhouse based on shape

§    Lean- to design

This is used when a greenhouse is placed against the side of an existing building. This design makes the best use of sunlight and minimizes the requirement for roof support. In actual practice, lean-to type is the cheapest to build.

  §    Even span greenhouse

In this, the two roof slopes are of equal width. It is easy to build. Shapes of greenhouses of are presented below. The evens pan greenhouse is most common in application.

§    Uneven span greenhouse

This has roofs of unequal width which make the structure adaptable to the side of a hill. This is rarely used now because they are adaptable for automation.

§    Ridge and furrow type (multi-span)

Ridge and furrow refer to two or more greenhouses connected to one another along the length of greenhouse. The side all is eliminated since it has single interior. It is generally used for carnations, rose, pot mums or crops that can tolerate comparable environmental conditions.

§    Gothic (pointed roof)

It is highly efficient, have a pleasant appearance and withstand wind due to its curved superstructure.

§    Quonset (semi-circular type)

The roof of this type of greenhouse will be semi-circular in shape. The roof covering may be either polythene, fiberglass or polycarbonate panels.

               Quonset Green House                                                                             Green House with bricks

§    Gome (ground-to-ground type)

These can be constructed by using steel tubing and either single or double polythene cover.

§    Tunnels

Whenever plants are to be protected from cold and frost for very short periods, tunnels of about 2 m height can be made by bending bamboo or steel tubes and covering with polythene. The poly cover and the tubing can be removed after use and store for future uses.

Figure-1 Shapes of green houses

Green House styles

Working principle of a greenhouse

Solar energy enters the greenhouse as short wave length radiation. Some amount reflects back and some hits on greenhouse objects and floor and turns into long wavelength radiations. The covering material is selective to these radiations. The cover is opaque to long wavelengths and it is trapped inside and increases the temperature inside. This is the principle of greenhouse. Environmental control inside a green house can be achieved by greenhouse cooling, shading and heating. Generally, the temperature inside greenhouse will always be higher than the ambient conditions depending on location, season and extent of ventilation provided. When ambient rises, the inside temperature also rises and this is not ideal for production of a good quality crop.

Method of construction of Green House

v  Site selection

The site selected should have proper drainage facility. A greenhouse needs dependable source of good quality water and electricity. Greenhouse should be located away from the buildings and trees to avoid obstruction of sunlight.

v   Orientation

In single span greenhouse, the orientation can be in any direction. But multi span greenhouses should be oriented in N-S direction in order to avoid shading effect. A free standing greenhouse that had its long axis perpendicular to the wind was relatively free from wind damages.

v   Fabrication of frame

A poly house of 300-500 sq.m area would be desirable for growing commercial flowers. To reduce cost of construction, depending on the size and durability of the structure, use of mild steel or GI pipes as structural frame is desirable.

v   Covering/ cladding/glazing material

Materials should be selected according to type of greenhouse, climate of place, crop requirement and economics. In India, polythlene film, acrylic and shade nets are commonly used as covering materials.

Most of the flower crops are either grown in raised beds or in metallic benches. Orientation of beds should be towards the length of greenhouses so that 45-60% of floor area can be utilized.

 Medium

Soil is the natural growing medium for most of the greenhouses from economical considerations. But it has drainage, pest and disease problems.

Irrigation or fertigation

Automatic watering systems through drips or overhead foggers are generally used depending on crop.

Choice of cultivar

In India, major demand is for deep color and it changes with season and occasion, color, productivity, disease resistance, vase life, growth rate, market demand and other characters also considered.

Green House technology commonly used for commercial purposes they are,

§   Cold frames

Traditional cold frames were essentially boxes in which to grow plants. They had low brick walls and transparent glass lids or lights that could be opened or closed. They were often built on the sides of greenhouses as a sort of halfway house between indoors and outdoors.

Cloches

Cloches can be moved from one part of the vegetable patch to another. Cloches are made of glass and clear plastic. They are useful at the beginning and end of the year. At the start of the season, they warm the soil before sowing or planting, then maintain the temperature as seeds germinate and seedlings develop. At the end of the season, they offer extra protection while late – harvesting crops ripen.

Tunnel cloches

They are called as continuous polytunnels, tunnel cloches are made from clear plastic film or fleece stretched over wire hoops.

Materials used for Green House

In temperature countries the greenhouse and conservatories are made of glass on frames combines of wood and either of these materials. The construction from foundation to plinth level may be either of brick or of stone and above this the iron or aluminium on which glass is put. Aluminium is rust-proof requiring no painting and in light in weight. Steel and wood need painting to prevent decay. All brick work should be 22.5 on thick. An alternative to glass is fibre-glass, which is though expensive initially does not incur recurring expenses. But fibre-glass will not admit as much light as glass-pane, glazed glasses are available for these develop scratches easily. The quality of glass planes used is usually called “double thick”, wire-mesh reinforced glasses are also available for the roofing for greater durability.

Advantages of greenhouse

• Plants can grow all seasons Variety of plants can raise
• Helps to protect pests and predators
• Helps to create the optimum growing environment Protect plants from poor weather
• Gives the concept of go green in our houses
• We can grow plants without dangerous pesticides Protect the beneficial insects into the greenhouse Easy to construct in our houses
• Gives pleasure to grow healthy plants and vegetables Helps to save energy
• Helps to free from stress.

Conclusion

Plants grown under cover, greenhouse are easier to protect from predators such as birds, mice, butterflies, moths and other insects while they are still small, tender and at their most vulnerable. A protected microclimate in which can sow seeds and raise seedlings and plants is easier and protect from all the seasons.

Web links

• nafis.go.ke>less>
• http://www.gothicarchgreen.wouse.com Dept8.washinton.ed
• http://en.wikipedia.org>
• www.thegardenfactor.co.uk