Material Selection for Greenhouse Construction:
Soilless agriculture is conducted under shade and it is also known as shade house agriculture. It is important the structure hosting the crop must be safe, cost effective and durable to adverse weather conditions and it should provide conducive environment. Initially the hydroponic agriculture was done in concrete structures that were quite difficult and time consuming to construct and above all much costlier for the farmers to afford.
However, with the passage of time, the introduction of polyethylene brought a revolution in hydroponic farming since the structure became far easier to construct apart from being less costly. During the last century considerable work has been done on materials for hydroponic structures. Generally the frames of the hydroponic structures are made of mild steel circular or square x-sectional pipes depending on the availability of materials.
The structures are clad with polythene, fiber glass, virus net, glass, tempered glass etc. All the cladding materials must be clear to allow sun light penetration. The roof of the structure must be in a slanting position to facilitate drainage of rain water. The smart designers of the structures make necessary arrangements to harvest the rain water falling on the roof and use the same for crop irrigation. It is ideal for the preparation of nutrient solution. Improvements in structural designs are under progress over the world and the farmers are developing even multi storied buildings for the purpose for creating controlled environment.
A heavy frame need support for fixing into the soil in order to assure structure resistance against wind storms, splashing rains and other weather conditions. For proper fixation of the frame, masonry foundation is essential around the periphery of the structure. Usually a stepped foundation with concrete underneath are used to support pillars of the frame.
Stronger the foundation, better it will be for stiffness of the frame. The support pillars of frame are concrete grouted into the foundation. Sometimes foundation is not continuous, rather the pillars are individually concrete grouted. However the individual grouting of pillars has poor resistance against storms and the pillars may uproot against heavy winds.
There are wide range of materials and designs of the frames. These are built with concrete, wood, bamboo, aluminum but the most popular material is mild steel or galvanized medium carbon steel. Circular pipes are used but the galvanized steel square pipes are most common. Design and shapes are variable and depend on the total width and length of the greenhouse or the tunnel. Frames can be also made of bamboo but their life span is very little because of weathering and termite effects. The PVC frames are easy to construct and these are also common. The general framing materials are;
- Mild Steel
It is a conventional framing material. Farmers construct rafts of wood and develop the frames themselves. The insulations can be easily nailed on to the wood. But the problem is that wood is susceptible to termite attack and it deteriorate soon. However, the quality of wood will always determine the life of structure. It is a good insulating material to work against high and low temperatures.
It is common constructional material for greenhouses. The workability of the bamboo is easy and the farmer can do it by himself. However, the attack of insects, termites and weathering is a big problem. Many farmers use bamboo for construction of their high tunnels for the reasons of low initial costs.
It is an expensive framing material for a greenhouse. It is easily workable and does not rust. Aluminum is light in weight and easy to handle. It does not rust like steel or rot like wood or degrade like PVC. It has a disadvantage of being weak compared with steel frames.
Mild steel is very common with all kind of galvanized circular, square and rectangular pipes. It needs a skilled person because it is welded using different fasteners.
It is light in weight and low in cost. Its workability is easy. It has a disadvantage that it is slightly weak in strength. It may bend against pressures.