In reality greenhouse is well-suited for small farms and where there are constraints on available land and water. However, in our country a small farmer simply does not look at the option of greenhouse because of the prohibitive capital costs.

Indeed, the need of the hour is to build cost-effective affordable greenhouses. Unfortunately, in India most of the green houses built with technologies from the Netherlands are so expensive, leave aside rich farmers, even corporate companies find them expensive.

This happened more so in many floriculture projects where the capital costs per hectare shot up to as high as Rs 1.5 to Rs 2 crore and the projects have instead of becoming profit centres havebecome huge losses.

It is startling to note that green houses built in many African and Latin American countries are costing 1/10th to 1/15th of the costs than that of normal Dutch technology and more importantly the produce coming out of such green houses is accepted by the market in the Netherlands. Obviously these units are making huge profits in relation to their counterparts in India.Obviously the key of success lies in the cheap, innovative greenhouse which will streamline the optimisation of all the inputs without any wastage whatsoever.

If we look to Israeli farmers we notice that they grow well over 35,00,000 roses per hectare per season in greenhouses. Averages of 300 tonnes of tomatoes are grown per hectare per season. And there are almost three seasons in about 13-14 months period. This production is four times higher than that harvested from open fields.

It is important to note that there are various types of greenhouses. For tomato planters the green house can be less sophisticated andcan be called nethouse. The whole idea of greenhouse technology is optimisation of all the inputs like nutrition, pesticide application, irrigation and light. In nethouse also one can control these factors and get the optimum results.Under the supervision of Biotechnology Resource Centre several nethouses in the various parts of Maharashtra are being constructed at very economical costs. The right choice of fertilisers is also important.

The application of growmore solid biofertiliser and Shoot Up and Growzyme liquid biofertilisers of Suvash Biogenics Pvt Ltd, have been giving expected yields for many floriculture greenhouses in Maharashtra and Karnataka.

Applications of Shoot Up and Growzyme in nethouses have given at three-four places the yield up to 450 tonnes of tomatoes per hectare in relation to normal 50-60 tonnes/hectare. In nethouses tomatoes and cucumbers are cultivated vertically up to as high as 15-18 feet.

It is very interesting to note that in Israel greenhouses are mainly used for growingflowers, vegetables, ornamental plants and herbs.

Recent experiments have even proved that fruit trees can be also grown in green houses. The fruits like peaches, loquats, grapes, and bananas for commercial purposes or for export purposes can be successfully cultured in greenhouses.

Plastic Covering
Plastic covering in greenhouses perform a variety of functions, including thermal disinfection of the soil prior to planting; covering the soil for heat collection; prevailing growth of weeds; minimising evaporation and escape of fertilisers like Growmore, Shoot Up and Growzyme, various size tunnels for all stages of plant growth; and spacious greenhouses designed for long-term use.

The covering is made of plastic (generally based on polyethylene and polycarbonate) and can also be produced according to a three-layer technology, providing the cover with special characteristics.

The plastic covering produced today is durable and resistant to vapours from sulphur used in pesticides in greenhouses.Attempts are being made to produce a thinner material without compromising its functionality. Thus, very thin mulch has been produced, to be used only in early stages of crop growth, which decomposes after a specified period of exposure to the sun's rays.

It may be noted that many greenhouse owners here and abroad using combination of biofertilisers like Growmore, Shoot Up and Growzyme have found that they have not to use pesticides at all. With a result apart from saving in pesticides they also get twin benefit of longer life of the green houses.

Today in Israel, the plastic sheeting manufactured is not only for covering structures, but also for controlling the spectrum of light rays that penetrate them and influence plant growth; as a filter to screen out or admit ultra-violet rays as needed; to radiate infra-red rays; and to refract and distribute light to maximise its beneficial effect on the plants. Some covers include additives that prevent water from dripping on the plants [anti-fog] and protectthe covering against degradation. The additions of various shades of colour also help combat pests.

Netting
Scales and mites carry viruses that have a devastating effect on plants and methods of controlling them are expensive. Many greenhouses, in addition to the plastic covering, have walls made up of netting that prevent the entry of scales and mites, and allow heat dispersal.

Other kinds of nets are used for shading, reducing the intensity of the sun's rays that reach the plants. These nets are categorised according to the percentage of shading they produce.

Advanced manufacturing methods have succeeded in producing netting that acts as a sophisticated thermal screen decreasing the sun's rays during the day, and preventing loss of heat at night. The new innovation is very useful where diurnal fluctuation are extreme. Such nets can be also used in poultry houses to increase the productivity.

Structure
The structure of greenhouses calls for a rigid, heavy covering, giving itsufficient durability to prevent it from being destroyed by strong winds and extreme climatic fluctuations. The greenhouses include curtains and skylights, and shade netting that includes automatic movement to sunlight reaction. The new greenhouses are taller, reaching the height of five metres at the lowest point. This provides better ventilation. It also allows for trellising greenhouse plants such as tomatoes, cucumbers and others.

Climate Control
An innovative technology developed in Israel allows cooling of the greenhouses by day and heating by night with a minimal investment of energy. This is accomplished via a shower system that sprays uniform-size drops and is installed at one end of the greenhouse.

During the course of the day, these drops absorb excess heat form the greenhouse and store it until nighttime, when the heat is released. This method is particularly useful to ornamentals, as they require more humid environment.

Pest Control
The Israeli development of a plasticcover that screens out UV rays, significantly decreases pest activity and prevents blackening of rose petals.Blue colour of the net changes the composition of light, which helps decrease the incidence of disease in cucumbers and tomatoes.

A new type of recently developed sheet attracts plant pest, which then stick to the plastic and die Another type of cover repels pests by its colour.The newly developed brown plastic cover prevents growth of weeds but allows penetration of the sun's rays for soil heating.

Computerised Greenhouse
Computer hardware and software have been developed in Israel, which allow automatic control of the greenhouse water, fertiliser and climate systems. Software developers maintain close contact with growers, in order to keep abreast of latest developments in agricultural systems and provide the most effective and advanced solutions.

(The Authors are associated with Biotechnology Resource Centre, Mumbai)