Protected cultivation practices can be defined as a cropping technique wherein the micro climate surrounding the plant body is controlled partially or fully as per the requirement of the vegetable species grown during their period of growth. With the advancement in agriculture various types of protected cultivation practices suitable for a specific type of agro-climatic zone have emerged. Among these protective cultivation practices, Green house, Plastic house, Lath house, Cloth house, Net house ,shade house, Hot beds and Cold frames etc is useful for the central India.
1. Green house
A greenhouse is a framed or an inflated structure covered with a transparent or translucent material in which crops could be grown under the condition of at least partially controlled environment and which is large enough to permit persons to work within it to carry out cultural operations.
Advantage of Green house:
REQUIREMENTS FOR GREENHOUSE CONSTRUCTION
Site Selection for the Greenhouse
Selection of geographical location of the land, price, transportation, and present and future effects of adjacent properties should be taken into consideration.
Topography of the Land
It determines the amount of work and expense that will be required to provide good surface drainage and efficient transportation.
Transportation in and Around the Greenhouse
This is an important factor. If the proposed site is hilly, it should be anticipated that considerable land preparation will be required. Access roads to the property will need to be large enough and surfaced to handle large motor freight equipment .The type of neighboring properties may have varied affects on the greenhouse plants. Greenhouse that were built outside of cities become surrounded by urban development with increased pressure of urbanization may develop problems in future.
Greenhouse businesses cannot have interruption of electrical service for more than a few minutes without serious consequences. Electrical shutdowns that are a nuisance for a machine shop could be a disaster for a greenhouse.
The quality and quantity of water that is available to the site must be determined.
If municipal water is available, usually it is acceptable for irrigation and for use in boilers with some treatment. When water has to be supplied by well or pond on the site, there are some potential problem. Extensive treatment may be needed for boiler, make-up water.
Economy of Construction
Ridge and furrow type construction is usually more economical and needs less land area. The house should be arranged in such a manner so that labour is conserved and the crop can be handled more effectively. The greenhouse should be constructed in such a way that vegetable can be harvested and moved to the marketable areas very easily.
Framework for Various Types of Greenhouse
The choice of materials for the framework of a greenhouse is based on structural strength, durability, initial cost, and maintenance costs. Wooden framework is used primarily for temporary or semi permanent structures. The most durable wood with the least maintenance cost is redwood. Steel framework has been used widely. This dose requires painting to prevent rust, but it is very satisfactory in other respects. Steel frame house may have redwood or aluminum roof and wall bars as well as ventilator sash. Aluminum has become increasingly popular for the greenhouse framework. The roof wall bars and ventilating sash all are made of aluminum. The corrosion problem with aluminum is slight, and the structure does not require painting. It should be kept in however, that the glazing procedure and maintenance are approximately the same for wood, steel, or aluminum.
COVERING MATERIALS FOR GREENHOUSE:-
The greenhouse must be covered with as clear a material as possible to provide the maximum amount of sunlight for the plants. the durability of the covering material, the initial cost, and the maintenance costs then determine the desirability of the material.Fiberglass, Poly Film etc is used as covering material for greenhouse.
HEATING AND COOLING OF GREENHOUSE
Accurate temperature control in the greenhouse is of great importance because the desired, best growth of vegetables occurs within a limited temperature range. Variations in this temperature may result in a complete lack of growth or extremely excessive development.
These are common use. The cheap houses are made of polythene and are widely used.
3. Shade houses:
Shade houses are made with straight sides and a flat top. The frame consists of cloth of light transmissing plastic; shade slightly lowers maximum daily temperature and slightly increases the relative humidity.
4. Lath houses:
Lath houses have straight sides and a flat top. The frame is similar to that of shad houses, but the cover is movable lath sash. Lath houses are usually used to protect high light sensitive plants.
5. Hot beds:
The frame of hot bed made of concrete blocks which acts as an effective insulator but obstruct light. Reinforced polyester plastic is also used for frame. It is light in weight, easy to handle and admits light, which however, is likely to decrease with age. Hot beds are headed with the help of different heating systems like hot air, hot water and electricity, which are adopted depending upon availability and cost, systems.
6. Cold frames:
The cold frame is made with frame and the cover. Cold frames are used to protect plants from frosts heavy rains and heavy winds. These are used in winter for raising herbaceous leafy vegetable plants. During summer, cover may be removed. Cold frames are of two types (i) temporary which is usually made of wood, and (ii) permanent which is made of concrete, concrete block and bricks.
Selection of vegetables:
The polyhouse cultivation is beneficial only when off- season vegetables are grown. It is also useful in production of vegetable nursery under adverse weather conditions. The choice of crops depends upon the size of the polyhouse structure, market demand as well as the expected market price. While it is convenient to raise any vegetable crop in environmentally-controlled polyhouse during any part of the year, the selection of crops is more critical in case of ordinary low-cost polyhouse. In subtropics, cucumber, bottlegourd, capsicum and tomato give quite reminerative yields during winter in low-cost polyhouses. With proper ventilation cabbage, early varieties of tropical cauliflower and coriander can be successfully grown during summer/rainy season also.
Under normal weather conditions it is possible to raise vegetable seedlings in open with ordinary care. But in some crops in certain seasons, the nursery is exposed to adverse weather which results in heavy mortality of the seedlings. For example in many subtropical areas the nursery period of early and mid season cauliflower coincides with the period of heavy rainfall.
Now it is well-established that if seeds of cucurbits are sown in small plastic bags during winter and the seedlings are reared in polyhouse, they remain safe from frost injury and become ready for transplanting early in February to give early and remunerative harvest.
The nutritional requirements of crops grown in a polyhouse are similar to those of open field grown crops. In polyhouse, the controlled irrigation, higher plant density and intensive cropping do not allow many weeds to grow.