Introduction Many of you might have heard about greenhouse farming but do not know actually what it is. A greenhouse is basically an enclosure made of wooden or metallic structure and covered with materials made of polyethylene or glass inside which crops are cultivated under strictly controlled climate. There is also another term poly house which is used quite often to mean the same thing. Actually the poly house is the type of greenhouse where the material used is polyethylene.
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Why Greenhouse farming Now you may ask why one chooses greenhouse farming. We all know that to get optimum production, crops need adequate sunlight, water, fertilizer, and pesticides. Due to the fluctuation in outside climatic conditions, the production varies in the open land. If there is excessive rain or drought the crops will be destroyed. The temperature also plays a big role and there are many crops that grow well under a certain temperature. The main advantage of Greenhouse farming is the crops can be grown inside the Greenhouse irrespective of the climatic conditions outside since the environment inside the Greenhouse is completely controlled. The temperature, water, moisture, and light are controlled manually/automatically according to the requirement of the crop and thus optimum production is possible.
Though in recent times greenhouse farming is gaining ground in India, Greenhouse farming is not so widespread though the country is largely dependent on agriculture. There are a few reasons for it. The initial investment in constructing the Greenhouse is much higher. Since there are many marginal farmers in our country they do not go for this high investment. It needs some technical awareness to manage a Greenhouse that is not possessed by many. Since Greenhouse farming is comparatively new, more promotion and initiative from the government is required.
Advantages of Greenhouse farming The yield in Greenhouse farming is almost 10 times more than open land farming and production is possible throughout the year since the environment is controlled and the selection of crops based on climatic conditions is not required. What's more, the reliability of the crops grown in Greenhouse increases a lot since the environment inside the Greenhouse is set according to our requirement. It is also to be seen that the requirement of water for cultivation is less and can be easily controlled. It should also be noted that with the use of organic fertilizers, the products are safe to consume. In fact, since the crops are cultivated inside the enclosure by the use of modern techniques, the crops are not susceptible to pest attacks.
Points to remember While constructing a Greenhouse, there are certain things that must be kept in mind. For one thing, while it is always profitable to grow crops in a Greenhouse when somebody is venturing out to Greenhouse farming for the first time, it would be a better option to start with a small area. Though the government provides subsidy up to a certain extent, it is better to get acquainted with the process before thinking of production on a large scale. Secondly, there are many training programs related to greenhouse farming conducted at various levels and it is always better to get the training before venturing out. Thirdly, it is necessary to enquire about the market of the product so the product is not wasted after harvesting. One must be aware of the government initiatives towards marketing the products and avail the opportunities in her/his area. Finally, an important thing is the selection of the crop. The crop should not be the one that has no market in the locality. Since the initial investment is very high, the crops which have a high commercial value and demand have to be selected.
In India, there is a high demand for exotic vegetables and cut flowers and therefore, they are grown in Greenhouse. Some of the common vegetables are Capsicum, Tomato, Red Cabbage, Spinach, and the common cut flowers are Dutch Rose, Gerbera, etc. Though, it is not limited to the cultivation of these vegetables and flowers only.
Cost of construction The cost varies according to the materials used and the total area of construction. This can vary from Rs.500/- to Rs.4000/- per square metre. For detailed information regarding various schemes of the government, one can visit the website of the National Horticulture Board
Controlling the greenhouse climate Modern technology has made automation a reality in almost every aspect and farming is no exception. While it is possible to construct a fully automated greenhouse, semi-automatic, or manually operated greenhouse costs much less and where the cost is a constraint one should go for the manual one.
Now, let's look at what are the controlling factors in a greenhouse. For any plants to grow the essential components are sunlight, water, air (Co2), and fertilizer. Pesticides are also used to keep away the pests. Along with these, the temperature and humidity are also controlled to get optimum production.
Sunlight Sunlight is an essential component and in a greenhouse, the sunlight is received through the polyethylene/glass cover of the structure. When sunlight is not required the artificial shades inside the greenhouse are used to cover the crops. If the sunlight is not sufficient due to external climatic conditions, artificial lights of high intensity can be used inside the greenhouse.
Carbon Di-Oxide The plants breathe in Carbon dioxide (CO2) and breathe out Oxygen (O2) during Photosynthesis and it is necessary to maintain the level of CO2 inside the greenhouse. Air vents inside the greenhouse and fans for horizontal airflow help to maintain and distribute the CO2 evenly but when the vents remain closed to maintain the level of other parameters, small CO2 generators where the combustion of propane or natural gas takes place are used. While using these CO2 generators it is a must to maintain the purity level of the fuels since too much impurity can damage the crops.
Humidity The relative humidity inside the greenhouse has to be kept within limits. High relative humidity increases the chance of infestation of diseases and reduces the growth of the plant. Therefore, the air must flow all over the plants which results in cooling to some extent and is accomplished by installing exhaust fans. The humidity is lowered very slowly when the growth rate of the crops increase and this can be done by controlling the speed of the exhaust fans.
Temperature Since the greenhouse is enclosed the outside temperature doesn't affect the inside atmosphere much. It is getting the sunlight during the daytime and because of the breathing of the plants inside the greenhouse, the air becomes heated. If the crops require a lower temperature then this excess heat is removed with the help of fans and opening up of the closed air vents. If too much cooling of the crops is required then an air conditioning system can also be installed.
Water, fertilizer and pesticides Watering the plants at regular intervals is essential and for that, a separate pipeline along with a pump is installed in the greenhouse. There are a few methods of watering the plants. Most widely used among them are Drip irrigation and Overhead sprinkler systems. In the drip irrigation system, individual pipelines are branched out from the main pipe and laid all over the place to cover the crop area. In every branch, there are water emission points at regular intervals that provide the required amount of water, pesticides and nutrients directly to the roots of the plants. In this system, the water and the pesticides enter the soil by the way of gravitational force as well as capillary action. The overhead sprinkler system is used mostly when the same crop is grown in the entire area. Here sprinklers are fitted on the pipes over the plants and they emit mist like water sprays over the entire area. A combination of both these can also be used depending on the area and type of crops.
Greenhouse types There are various types of Greenhouse based on the construction and it is hard to differentiate between them since almost all of them have pros and cons. Based on the shapes of the greenhouse, a few common construction types are described below with a picture for representation.
Image source: Self-created on paint
Post and rafter This is one of the popular designs because of the simplicity in construction. These types are covered with glass or glazing panels made from polycarbonate. Here the utilization of space inside the greenhouse is very good and the air circulation is efficient. One of the disadvantages of this design is more materials are required for construction compared to other types.
Quonset Style Greenhouse From the picture, it can be seen that this is a semi-circular type and resembles a half-cut barrel. These are made of metal or PVC pipes. Here the greenhouse is ventilated through the big doors situated at both ends or by rolling up the sidewalls. Films made of polyethylene are used to cover the structure. Because of its structure, it gets most of the sunlight. The frame of this type is not that strong compared to Post and Rafter or A-type.
Gothic Arch The roof of this type is pointed because here the walls of both sides are bent over the frame. Plastic sheets are used to cover this type of greenhouse. The design is very simple and since plastic sheets are used the cost is much less. Because of the bent, the height of the sidewalls is a bit lower which can reduce the storage space.
A-frame The frame and structure of this type are A-shaped and hence the name. This is also a common type because of the simplicity in design. Compared to Post and Rafter design, the materials required are less and this one is covered with glass or translucent glazing panels. The sidewalls are narrowed down at the upper side so efficient use of the entire greenhouse can be a problem.
Rigid-frame The structure is quite tough as very strong truss are used as support. Polycarbonate or glass is used as the covering material in this structure. Since this type is not very big, crops that require mass growth is not cultivated here.
Conclusion While the basics of a greenhouse are covered here, there are many things that one must know before starting greenhouse farming. Each of the crops requires certain protective measures and the greenhouse structure can be of different design based on the requirement. A proper enquiry of the land where the greenhouse is to be constructed has to be carried out prior to applying for subsidy and after collecting the necessary information one must approach the local agriculture/horticulture board to know all the procedure in details.