The main purpose of greenhouse technology is to provide a good growing environment for successfully growing high quality plants round the year. In developed countries, the climatic conditions are mild in general. The growing of fruits, flowers and vegetables under polyhouse is common practice. Greenhouse structures are commonly used to grow off-season horticultural crops when the conditions are not favourable for their normal growing. Greenhouse ensures continuous supply of fruits, vegetables and flowers throughout the year. The controlled environment/techniques like plastic greenhouses would be essential to promote agriculture particularly in the prevailing varied range of agro-climatic conditions in the country.
Greenhouses are structures covered with transparent to translucent materials such as LDPE, FRP and Polycarbonate sheets etc. which allows the solar radiation to pass through, but traps the thermal radiation emitted from the objects within. This creates a congenial environment for plant growth. Energy received from the sum is converted to heat within the greenhouse during the day as well as used for evaporate water during the normal transpiration of plants. The various parameters influencing plant growth such as Light, heat, CO2 and moisture could be controlled in these structures.
The cost of basic structure for housing rigid or flexible covering material depending upon the structure materials selected such as G.I. pipe, M.S. angles, fibre glass reinforced polyester, glass, acrylic etc. Besides the cost of setting-up of greenhouse also depends on the covering materials used.
Such as greenhouses made of costly materials as mentioned above are however expensive and beyond the means of the average Indian farmer. To overcome these problems and to suit to farmer's economy in construction of these greenhouses in their field, a low cost wooden structure has been designed and field-tested. These structures are suitable for any covering materials like film plastic sheets, shaded nets, UV stabilized LDPE film sheets. The procedure for erection of such greenhouses are explained in this manual to facilitates a greenhouse user to have more space within the greenhouse, to carry out various agricultural practices.
The results obtained from the plant grown under these greenhouses suggest that this might be a feasible technology for small and marginal farmers as it result in a much higher yield and enables growing off season crops like vegetables.
Selection of wooden poles play an important role in structure strength. Eucalyptus poles have many advantages than Casuarina poles as termite and fungal attacks are very minimal on Eucalyptus poles. Moreover, if nailed, these poles will be intact and its layers may not peel away because of good fibre strength.
Two sizes of wooden poles are normally used. One is of larger diameter 7 to 10 cms and other is around 5 cms diameter. The large size stems are used for the main structure and smaller size stems are used for the main structure and smaller size stems are used for the supporting structure.
No. of Poles required
Large diameter poles : 21 nos.
Small diameter poles : 34 nos.
Total no. of poles required : 55 nos.
Long wire nails are used for fixing the wooden poles with supporting poles as well as in the pole joints.
Nails required 7 cms long : 3 kg
The structures are suitable for any flexible greenhouse covering materials.
LDPE (Low density polyethylene) film is the most commonly used for greenhouses in the world. Moreover they are less expensive and easy to install. In India, LDPE films manufactured by Indian Petro Chemicals Ltd (IPCL) have many features and most suitable covering material for these wooden structured greenhouses. In our experience we found that IPCL LDPE film has many advantages and the parameters influencing plant growth such as light heat, CO2 and relative humidity are well maintained under these coverings.
Total film required
The film (U.V. Film Low Density Polyethylene Film) required is about 2.48 times more than the floor area. E.g. to construct a greenhouse of 35' x 20' = 700 sq.ft. will require 1736 sq.ft. of UV film having total weight of approximately 30 kilograms having thickness of 200 microns.
Ordinary LDPE film roll/leftover UV stabilised LDPE film roll of 10 cms width should be prepared to wrap all the poles, joints and wires to avoid direct contact with the UV stabilised LDPE film.
Total film required in kgs: 3 kgs
Plastic ropes are used to sandwich over the LDPE sheet between the truss structure and the rope itself. This is to prevent any fearing of the sheet due to excessive wind force.
Plastic rope required: 5 kg
Bamboo is used along a perimeter connecting the joints over the top in order to support the LDPE sheets that are laid over them.
Total no. of bamboo sticks required: 30
Tag nails are used with rubber washer to tag the LDPE sheets with the wooden truss structure. These tag nails are used to fix the sheets firmly on the wooden poles so as to fasten the sheets uniformly on the truss structure.
Tag Nails required (1" length): 250 gms
STEP 1- SITE SELECTION AND ORIENTATION OF GREENHOUSE
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