ABSTRACT
India has a wide spectrum of diverse agro-climatic conditions but vegetable cultivation practices in India have been generally restricted to regional and seasonal needs. Although the production of vegetables has increased to a level of 94 million tons, still the technology used and practices followed are predominantly traditional, resulting in low yields and inconsistent quality and quantity of produce supplies to the markets. In several parts of the country, especially in the northern plains, the soils are highly fertile but temperatures extremes ranging from 0°C to 48°C during a year do not allow year-round outdoor vegetable cultivation. Protected structures modify these extremes to a greater extent to grow vegetables almost year-round. In the upper reaches of the Himalayas, cold desert conditions prevail, where the temperature is extremely low (−5°C to −30°C) during winter season and the region remains cut off from the rest of the country from November to March due to heavy snowfall. It is, therefore, difficult to grow vegetables in such a climate, but some specific protected structures, called poly-trenches, have proved to be very useful for vegetable cultivation as the region receives an abundance of sunshine (Indian Society of Vegetable Science Souvenir, 1998; Phookan and Saikia, 2003). Similarly, in several parts of the country, biotic stresses during the rainy and post-rainy season do not allow successful vegetable cultivation. As a result, most of the vegetables are damaged by the severe incidence of viruses. Protected structures covered with insect proof nets (insect proof net houses) provide a big opportunity of virus-free vegetable cultivation even on a commercial scale. Protected conditions for vegetable cultivation are created by using different types of structures, which are season and location specific. These structures are designed as per the climate modification requirement of the area. Temperature, humidity, wind velocity, soil conditions, etc. also play a major role in the design of protected structures for growing vegetable crops, but there are several constraints and problems which restrict protected cultivation of vegetable crops (Rai et al., 2004; Singh, 1998; Singh et al., 1999; Anonymous, 2002). It is, therefore, necessary to work out the best-suited design of protected structures for different climatic conditions along with their techno-economic feasibility.
