Polytunnel

Temperate regions Polytunnels are mainly used in temperate regions in similar ways to greenhouses and cloches (row covers). Modern designs allow sowing and harvesting machines to move inside the structures, automating production. Polytunnels have had a significant effect on the production of strawberries in the United Kingdom. Other soft fruits such as raspberries and blackberries are also cultivated in the same way. In colder regions such as Quebec, Canada, they extend the growing season by 2-3 months. Also, local manufacturing such as Industries Harnois are now producing high tunnels locally in North America. Tropical regions In a tropical climate, temperatures are prone to soar above all normal levels. In such cases, foggers/misters are used to reduce the temperature. This does not increase the humidity levels in the polytunnel as the evaporated droplets are almost immediately ventilated to open air. High-tech poly houses even have space-heating systems as well as soil-heating systems to purify the soil of unwanted viruses, bacteria, and other organisms. The recent Indo-Israel collaboration at Gharunda, near Karnal in India, is an excellent example of polyhouse farming taking place in a developing country. Christine Allen, of CAFOD, describes areas of Kenya where there are "vegetable-filled polytunnels as far as the eye can see", but notes that they primarily serve the export market rather than providing food for domestic consumption. If developing countries were to develop a special incentive program solely for fruit-and-vegetable farmers, especially in demographically large nations like India, then the migration rate from rural to urban areas (as well as the loss of horticultural and fruit/vegetable farmers) to urban areas may be reduced. This brings a huge potential to improve the farming sector, which is key to long-term economic stability. The small polytunnels used by each farmer in each village promote the cultivation of vegetables both on-season and off-season, and would actually help to moderate the market rate for fruit and vegetables in long run, on a year-round basis, and would help to satisfy local market needs. For example, in India, the inability to grow tomatoes generates price spikes during the monsoon season. This is seen as an ideal time to grow tomatoes in polytunnels, since they provide the ideal climate for the crop. In India, the Abhinav Farmers Club grows flowers and organic vegetables in polytunnels. ==Development==

Hoophouses have existed at least since the 1940s, but they are much more commonly used with each passing decade, and their design continues to evolve. Because of the wide variety of constantly changing designs, in reality there is an entirely continuous spectrum from high tunnels through low tunnels to the simplest row covers, although they are often thought about as discrete steps. Major themes of continuing development are (1) achieving the same results with lighter construction and less cost and (2) making hoophouses easily movable. The advantages of mobile hoophouses include greater return on investment (with the same unit of investment getting greater use per year across different crops in different months) and more flexibility on crop rotation without ever having to bother to dig the soil out of a stationary house (or use soil steam sterilization) to cure greenhouse soil sickness. A US Department of Agriculture program is helping farmers install polytunnels. The program was announced at the US White House garden in December 2009. Farmers in Iraq are building these in increasing number and adding drip irrigation to grow tomatoes. == References ==