Approximately 92 percent of man-made plants are now cultivated in the open field. Farmers have had to deal with the growth circumstances provided by Mother Nature from the dawn of agriculture. In temperate places where climatic conditions are harsh and no crops can be cultivated, man has created technical techniques of cultivating high-value crops by giving protection from extreme cold and heat. Greenhouse Technology is the term for this.
“The science of supplying plants with a favourable environment is known as greenhouse technology.” It also protects plants from harmful environmental factors including wind, cold, precipitation, excessive radiation, severe temperature, insects, and illnesses. Around the plants, a perfect microclimate may be established. Greenhouses are framed or inflatable buildings coated in transparent or translucent material that are big enough to produce crops under partial or complete environmental control for optimal development and yield.
TYPES OF GREENHOUSES
Crop cultivation takes place in a variety of greenhouse buildings. Although each form has advantages for a certain purpose, there is no single style of greenhouse that can be considered the finest in general. Greenhouses come in a variety of shapes and sizes to satisfy a variety of requirements. The following is a list of the various types of greenhouses, organised by shape, use, material, and construction:
Greenhouse Type Based On Shape:
The peculiarity of the cross section of the greenhouses might be regarded a criteria in categorization. The following are the most popular types of greenhouses based on their shape:
- Greenhouse with a slant to it.
- Greenhouse with an even spread.
- Greenhouse with an uneven spread.
- Ridge and furrow is a form of ridge and furrow.
- Type with saw tooth.
- Greenhouse made of Quonset huts.
- Quonset greenhouse with interlocking ridges and furrows.
- Greenhouse built from the ground up.
Lean-to type greenhouse
When a greenhouse is built against the side of an existing structure, it is called a lean-to. It is constructed against a building, with one or more of its sides utilizing the existing framework (Fig.1). It is typically attached to a home, although it can also be attached to other structures. The building’s roof has been expanded with greenhouse covering material, and the space is adequately covered. It is usually located on the south side. Single or double-row plant benches with a total width of 7 to 12 feet are limited in a lean-to greenhouse. It can be as long as the structure to which it is linked. For adequate sun exposure, it should face the optimal direction.
The following are some of the benefits of a lean-to greenhouse:
- It’s generally close to power, running water, and heat.
- It is the cheapest building.
- This design maximises the use of natural light while reducing the need for roof supports.
The following are some of the disadvantages of a lean-to greenhouse:
- There is a lack of room, light, ventilation, and temperature regulation.
- The design’s maximum size is limited by the height of the supporting wall.
- Temperature regulation is more challenging since the greenhouse’s wall may gather heat from the sun while the greenhouse’s translucent cover loses heat quickly.
Fig. 1- Lean-to-type type greenhouses
Even span type greenhouse
The even-span structure is the most common and full-size construction, with equal pitch and breadth on both roof slopes (Fig.1.3.2). This design is appropriate for a small greenhouse that is built on level ground. One gable end is linked to a home. It may hold two or three rows of plant benches. An even-span greenhouse costs more than a lean-to greenhouse, but it offers more design freedom and allows for more plants. The even-span will cost more to heat due to its size and larger quantity of exposed glass surface. The design has a superior shape for air circulation than a lean-to type for maintaining consistent temperatures during the winter heating season. Unless the construction is extremely near to a heated building, a separate heating system is required. Two side benches, two pathways, and a broad centre bench will be included. In different parts of India, there are several single and multiple span kinds to choose from. The spread of a single span type varies from 5 to 9 metres, while the length is roughly 24 metres. The height ranges between 2.5 and 4.3 metres.
Fig- 2. Even Span Type Greenhouse
Uneven span type greenhouse
This sort of greenhouse is built on a mountainous site. The roofs are of varied breadth, allowing the structure to adjust to hillside slopes (Fig..3). This sort of greenhouse is no longer often utilised since it cannot be automated.
Fig 3. Uneven Span Type Greenhouse
Ridge and furrow type greenhouse
Two or more A-frame greenhouses are joined along the length of the eave in this style of design (Fig. 1.3.4). Rain and melting snow are carried away by the eave, which acts as a furrow or gutter. Between the greenhouses, a side wall is removed, resulting in a building with a single huge interior. Interior space consolidation decreases labour, lowers automation costs, enhances personal management, and lowers fuel consumption by reducing the amount of exposed wall surface through which heat escapes. Snow loads must be included into the frame requirements of these greenhouses since snow does not fall off the roofs like it does in individual free-standing greenhouses, but rather melts. Ridge and furrow greenhouses are widely utilised in northern Europe and Canada, despite the presence of snow, and are well adapted to Indian climate.
Fig. 4. Ridge and furrow type greenhouses
Saw tooth type Greenhouse
These greenhouses are identical to ridge and furrow greenhouses, with the exception that natural ventilation is provided. In a saw-tooth type greenhouse, a certain natural ventilation flow route (Fig. 5) arises.
Fig. 5. Saw tooth type greenhouses
The pipe arches or trusses in this greenhouse are supported by pipe purling that runs the length of the greenhouse (Fig. 1.3.6). Polyethylene is the most common covering material for this style of greenhouse. These greenhouses are usually less expensive than gutter-connected greenhouses and are beneficial when only a small, isolated culture area is required. These dwellings are joined either in a free-standing manner or in a ridge and furrow pattern. The interlocking form has truss elements that overlap enough for a plant bed to develop between the overlapping areas of neighbouring homes. For a group of dwellings of this sort, a single vast cultural space exists, a configuration that is more suited to automation and labour movement.
Fig. 6 Quonset Type Greenhouse
Greenhouse Type Based on Utility
The functions or utilities can be used to classify the items. Artificial cooling and heating are the most expensive and complex of the several utilities. As a result, they are divided into two categories.
- Greenhouses that are used for active heating.
- Greenhouses are used to provide active cooling.
Greenhouses for active heating
The air temperature within the greenhouse drops at night. To keep plants from getting a chilly bite from freezing, some heat must be provided. The amount of energy required to heat a greenhouse is determined by the pace at which heat is lost to the outside environment. To prevent heat losses, many technologies are used, such as double layer polyethylene, thermo pane windows (two layers of factory sealed glass with dead air gap), or heating systems such unit heaters, central heat, radiant heat, and solar heating systems.
Greenhouses for active cooling
For optimum crop development throughout the summer, it is preferable to keep greenhouse temperatures lower than ambient temperatures. As a result, appropriate changes to the green house are made to allow huge quantities of cooled air to be brought into the greenhouse. This form of greenhouse uses either an evaporative cooling pad with fan or fog cooling. This greenhouse is built in such a way that it allows for a roof opening of up to 40%, and in some circumstances up to 100%.
Greenhouse Type Based on Construction
The structural material has the most influence on the kind of construction, but the covering material has an impact as well. The material should be stronger as the span increases, and more structural elements should be employed to create stable tissues. Simple designs, such as hoops, can be used for shorter spans. Greenhouses may be classed as follows based on their construction.
- The building is made of wood.
- Structure made of pipes.
- The construction is framed by trusses.
Wooden framed structures
In general, only timber framed buildings are utilised for greenhouses with spans smaller than 6 m. Without the use of a truss, the side posts and columns are made of wood Pine wood 8 is a popular choice since it is both affordable and strong. Timber with high strength, durability, and machinability that is locally accessible can also be utilised for the construction.
Fig Wooden Framed Greenhouses
Pipe framed structures
When the clear span is roughly 12m, pipes are utilised to create greenhouses. Pipes are used to make side posts, columns, cross ties, and purlins in general. The trusses aren’t employed in this design.
Fig- Pipe Framed Greenhouse Structures
Truss framed structures
Truss frames are utilised if the greenhouse span is more than or equal to 15 metres. A truss is made up of rafters, chords, and struts that are welded together from flat steel, tubular steel, or angular iron. Struts are compression support members, whereas chords are tension support members. Each truss is fastened to angle iron purlins that run the length of the greenhouse. Only very broad truss frame homes of 21.3 m or more utilise columns. The majority of the glass houses use truss frames, which are ideally suited for pre-fabrication.
Fig -Truss Framed Greenhouse Structures
Greenhouse Type Based on Covering Material
The greenhouse structure’s main and most significant component is the covering materials. Covering materials have a direct impact on the greenhouse effect within the building, as well as the air temperature within it. The types of frames and methods of attachment differ depending on the covering material. Glass, plastic film, and rigid panel greenhouses are categorised based on the type of covering materials used.
Prior to 1950, only glass greenhouses with glass as the covering material existed. The use of glass as a covering material has the benefit of allowing more light into the interior. The air penetration rate in these greenhouses is greater, resulting in decreased interior humidity and improved disease prevention. For the building of a glass greenhouse, lean-to, even span, ridge and furrow designs are employed.
Fig. Glass Greenhouse
Plastic film greenhouses
In this form of greenhouse, flexible plastic films such as polyethylene, polyester, and polyvinyl chloride are employed as the covering material. Plastics have become popular as a greenhouse covering material since they are inexpensive and have lower heating costs than glass greenhouses. The biggest drawback of plastic films is their limited lifespan. The finest ultraviolet (UV) stabilized film, for example, can only last four years. This covering material is suited for use in both Quonset and gutter-connected designs.
Fig. Polyethylene film greenhouse
Rigid panel greenhouses
In quonset or ridge and furrow type frames, rigid polyvinyl chloride panels, fibre glass-reinforced plastic, acrylic, and polycarbonate rigid panels are used as the covering material. When compared to glass or plastic, this material is more resistant to fracture and the light intensity is uniform throughout the greenhouse. High-quality panels can last for up to 20 years. The primary downside is that these panels are prone to collecting dust and harbouring algae, resulting in panel darkening and a loss in light transmission. There is a substantial risk of a fire.
Fig. Polycarbonate Covering
Greenhouse Type Based on Cost of Construction
Based on the building costs involved;
- Greenhouses are expensive.
- Green House at a Reasonable Price
- Greenhouses at a Low Cost
There are several types and varieties of plants that grow naturally in a wide range of climate settings and have been transported from their native habitats to regulated agricultural environments by modern agriculture. As a result, for each type and variety of plant, circumstances that are comparable to those found in nature must be developed. Each stage of a cultivated plant’s development necessitates the application of a certain form of shadow. The shade nets do a good job of providing the plants with the right microclimate. Shade nettings are used to protect crops and plants from UV radiation, as well as extreme weather conditions such as temperature changes, heavy rain, and strong winds. Due to the regulated micro-climate conditions “made” in the covered area using shade netting, better crop growth conditions can be reached, resulting in increased agricultural yields. All nettings are UV stabilized to ensure that they last as long as possible in the exposed region. They have a strong tear resistance, a low weight for easy and rapid installation, and a shade value range of 30-90 percent. In the market, there is a wide range of shading nets that are classified by the degree of shade they provide to the plant growing beneath them.
- Basics of Silviculture
- Agriculture History of India
- Silvicultural System of Concentrated Regeneration
- Coppice System of Silviculture
- Branches of Horticulture