Advantages of greenhouses: 

1. The yield is maybe 10-12 times higher than that of outdoor cultivation depending upon the type of greenhouse, type of crop, environmental control facilities.
2. The technology is ideally suited for vegetables and flower crops where uniformity in yield is very important.
3. Year-round production of floricultural crops and Off-season production of vegetable and fruit crops is possible.
4. Disease-free and genetically superior transplants can be produced continuously.
5. Efficient utilization of chemicals, pesticides to control pests and diseases and efficient use of Water.
6. Production of quality produces free of blemishes.
7. Most useful in monitoring and controlling the instability of the various ecological system. 

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Greenhouses – World Scenario 

There are more than 50 countries now in the world where the cultivation of crops is undertaken on a commercial scale undercover. The major countries are the USA, Spain, Canada, and The Netherlands. In Asia, China and Japan are the largest users of greenhouses. The United States of America has a total area of about 4000 ha under greenhouses while Spain has been estimated to have around 25,000 ha and Italy 18,500 ha. The Netherlands is the traditional exporter of greenhouse-grown flowers and vegetables all over the world. With about 89,600 ha undercover, the Dutch greenhouse industry is probably the most advanced in the world. The development of greenhouse technology in China has been faster than in any other country in the world. With a modest beginning in the late seventies, the area under greenhouses in China has increased to48,000 ha in recent years. Japan also has more than 40,000 ha under greenhouse cultivation of which nearly 7500 ha is devoted to only fruit orchards.











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Status in India 

In India the use of greenhouse technology started only during the 1980’s and it was mainly used for research activities. This may be because of our emphasis, so far had been on achieving self-sufficiency in food grain production. However, in recent years in view of the globalization of the international market and tremendous boost and fillip that is being given for export of agricultural produce, there has been a spurt in the demand 4 for greenhouse technology. The National Committee on the use of Plastics in Agriculture(NCPA-1982) has recommended location-specific trials of greenhouse technology for adoption in various regions of the country. The commercial utilization of greenhouses started from 1988onwards and now with the introduction of Government’s liberalization policies and developmental initiatives, several corporate houses have entered to set up 100% export oriented units. In just four years, since the implementation of the new policies in 1991, 103 projects with foreign investment of more than `.80 crores have been approved to be set up in the country at an estimated cost of more than `.1000 crores around Pune, Bangalore, Hyderabad, and Delhi. Thus the area under climatically controlled greenhouses of these projects is estimated to be around 300ha. Out of which many have already commenced exports and have received very encouraging results in terms of the acceptance of the quality in major markets abroad and the price obtained.

Indian Context with its severe land fragmentation precision farming has to do more with the precise application of agricultural inputs based on soil, weather and crop requirement to maximize sustainable productivity, quality, and profitability.

Hi-tech Agriculture is one method of precision farming on a smaller scale where plant protection and fertigation are applied at the root zone and plants are grown in precise conditions of temperature and humidity for uniformity and maximization of yield. There are two approaches viz., Greenhouse/poly house system and open-air system.

Growing of crops in greenhouses has proved to be the best way of utilizing the potential of the crop. Computerized control of irrigation, fertilization (Fertigation) and microclimate in greenhouse enable precise monitoring of the most important production practices. In temperate regions where the climatic conditions are extremely adverse and no crops can be grown high-value crops can be grown continuously by providing protection from the adverse climatic conditions such as wind, cold, precipitation, excessive radiation, extreme temperature, insects and diseases through Greenhouse Technology.

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Components and Features

Polythene Polyhouse / Greenhouses are made of transparent, tight, cheap and flexible polythene. This enables the cultivation of vegetables and other crops in any season of the year depending upon their requirement because temperature and humidity can easily be controlled in Polyhouses as they prevent the thermal radiation from escaping which increases the temperature and energy and thus helps in the process of photosynthesis. It is well established that for the production of energy vegetable, fruits, and flower crop, the playhouses are constructed with the help of ultraviolet plastic sheets, so that they may last form 6 Sheets are usually of 1501-micron thick plastic sheet and draped around a bamboo or iron pipes which are more durable but costlier.

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Heating Systems 

Heating is usually required in the winter season. Generally, the solar energy is sufficient to maintain inner temperature of playhouse but when this is insufficient, via media like construction of a tunnel below the earth of playhouse, covering the northern wall of the house by jute clothing, covering whole of the playhouse with jute cloth during night and installing solar heating systems can be considered.








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Cooling systems 

In the summer season when the ambient temperature rises above 400C during the daytime, the cooling of polyhouse is required. This is done by providing adequate ventilation and removing the internal air of polyhouse out of it in a natural manner or by installing high power fans which need to be switched on at regular intervals. Installation of cooler on eastern or Western Wall can also be done to keep the temperature low and maintain proper humidity. Alternatively, a Water-misting mechanism can be installed.

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Shading systems 

Certain plants are damaged due to very high light intensity during summer. Shading reduces the light intensity and cools the microclimate inside the greenhouse. Shade paints (lime or Redusol or Vari clear), agro-shade nets or retractable thermal screens are generally used and operated manually or through automatic devices.




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Watering systems 

Water quality is very important and often overlooked. Total salt-content levels, alkalinity levels, the balance of individual ions such as boron and fluoride can all have a serious bearing on crop success. The water sources should be tested before a greenhouse is established. The electrical conductivity level should be 0.75 – 1.5 dS/m and a pH of 6-7. The automatic watering system through drips or overhead foggers is generally used depending upon the crop.

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Fertigation

It varies from single broadcasting of fertilizers to the use of soluble grade fertilizers over different operating systems. One of the most modern technologies is currently offered by Priva – Phillips Nutriflux or Van Vliet Midi Aqua Flexilene System. Both the system have nutrient plant demand for nutrients in relation to EC/pH of the media, temperature, RH, light intensity, crop growth, mineral deficiency, etc.

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Photoperiod control 

Several plant species flower only when they are exposed to specific light duration. The yield and quality of flower crops could be increased with artificial lighting during night hours. Cyclic lighting is most effective. Short day conditions in greenhouses can be created with a fully automatic, semi-automatic or manual ‘blackout’ system using good quality black polythene sheets, especially for chrysanthemum.

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Control system

A manual or semi-automatic control system is less capital intensive but requires a lot of attention and care. Recently, computerized control systems are available which can integrate temperature, light intensity, relative humidity, CO2, plant moisture, nutrient requirement, and plant-protection measures.


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Equipment’s needed

In case of permanent polyhouse structure, steel and fiber made glass are galvanized hallow pipe-having glass or transparent polythene sheet structure is needed. For small farmers they can build up the polyhouse they require bamboo structure on which polythene sheet is used for the cover purpose. For irrigation facility, sprinkler irrigation unit is needed, while for controlling the air temperature ventilators are required.

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Roof of Polyhouse 

In the case of construction of polyhouse plastic film, nylon, acrylic, vinyl, polycarbonate and polyethylene film can be used for the roof purpose. At present among the available poly film, the use of a film of 200 microns or 800 gauge thickness ultraviolet protective film is considered. The framework of polyhouse should be made of G.I. pipe.


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Watering system 

The micro-irrigation system is the best for watering plants in a greenhouse. Micro sprinklers or drip irrigation equipment can be used. In micro-sprinkler system, water under high pressure is forced through nozzles arranged on a supporting stand at about 1 feet height. This facilitates watering at the base level of the plants.


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Disc filters

Used to remove fine particles suspended in water Screen filters: Stainless steel screen of 120 mesh (0.13mm) size. This is used for the second stage filtration of irrigation water. Fertigation system Fertigation systems are automatic mixing and dispensing units which consist of system pumps and a supplying device. The fertilizers are dissolved separately in tanks and are mixed in a given ratio and supplied to the plants through drippers.

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Fertilizer Injectors 

Fertilizer injectors are of two basic types. Those that inject concentrated fertilizer into water lines on the basis of the venturi principle and those that inject using positive displacement. Basically, these injectors work by means of a pressure difference between the irrigation line and the fertilizer stock tank. These injectors are inexpensive and are suitable for small areas. Large amounts of fertilizer application would require huge stock tanks due to its narrow ratio. General problems of fertigation Nitrogen tends to accumulate at the periphery of wetted soil volume. Hence, only roots at the periphery of the wetted zone alone will have enough access to Nitrogen. Nitrogen is lost by leaching and denitrification. Phosphorous accumulates near emitter and P fixing capacity decides its efficiency. Potassium moves both laterally and downward and does not accumulate near emitter. Its distribution is more uniform 9 than N&P. Excepting boron, all micronutrients accumulate near the emitter if supplied by fertigation. Boron is lost by leaching in sandy soil low in organic matter. But chelated micronutrients of Fe, Zn can move away from the emitter but not far away from the rooting zone.

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Media preparation 

The media used in the greenhouse generally have physical and chemical properties that are distinct from field soils. A desirable medium should be a good balance between physical properties like water holding capacity and porosity. The medium should be well-drained pH of 5.0 to 7.0 and the soluble salt (EC) level of 0.4 to 1.4 dS/m is optimum for most of the greenhouse crops Low pH can be raised by using amendments like lime (calcium carbonate) and dolomite (Ca-Mg carbonate) and basic, fertilizers like calcium nitrate, calcium cyanamide, sodium nitrate and potassium nitrate while high pH can be reduced by amendments like sulphur, gypsum and Epsom salts, acidic fertilizers like urea, ammonium sulphate, ammonium nitrate, mono ammonium phosphate and aqua ammonia and acids like phosphoric and sulphuric acids. It is essential to maintain a temperature of the plug mix between 70 to 75ºF. Irrigation through the mist is a must in plug growing. Misting for 12 seconds every 12 minutes on cloudy days and 12 seconds every 6 minutes on sunny days is desirable. The pH of water and mix should be monitored regularly.


Linkages – Backwards and Forwards 

A. Procurement of Planting Material:
The planting material (seedlings) can be procured from approved centers managed by the Department of Agriculture or from the different campuses of the Agricultural Universities and KVKs and also from approved private nurseries.
B. Transport: Normally, vegetables and flowers immediately after harvest is graded, packed, and sent to the market. Thus, as such, there is no need for precooling or refrigerated van to transport the produce.
C. Marketing: Vegetables so cultivated have good and robust demand in the major cities of Kerala. However, for effective price realization branding may be necessary at a local scale and dedicated marketing channels can be thought of.

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