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A polytunnel (also known as a polyhouse, hoop greenhouse or hoophouse, grow tunnel or high tunnel) is a tunnel typically made from steel and covered in polyethylene, usually semi-circular, square or elongated in shape. The interior heats up because incoming solar radiation from the sun warms plants, soil, and other things inside the building faster than heat can escape the structure. Air warmed by the heat from hot interior surfaces is retained in the building by the roof and wall. Temperature, humidity and ventilation can be controlled by equipment fixed in the polytunnel or by manual opening and closing of vents. Polytunnels are mainly used in temperate regions in similar ways to glass greenhouses and row covers. Besides the passive solar heating that every polytunnel provides, every variation of auxiliary heating (from hothouse heating through minimal heating to unheated houses) is represented in current practice. The nesting of row covers and low tunnels inside high tunnels is also common. [1]
Polytunnels can be used to provide a higher temperature and/or humidity than that which is available in the environment but can also protect crops from intense heat, bright sunlight, winds, hailstones, and cold waves. This allows fruits and vegetables to be grown at times usually considered off season; market gardeners commonly use polytunnels for season extension. [2] Beyond season extension, polytunnels are also used to allow cold-hardy crops to overwinter in regions where their hardiness is not quite strong enough for them to survive outdoors. Temperature increases of only 5 to 15 °C (9 to 27 °F) above outdoor ambient, coupled with protection from the drying effect of wind, are enough to let selected plant varieties grow slowly but healthily instead of dying. The effect is to create a microclimate that simulates the temperatures of a location several hardiness zones closer to the equator (and protects from wind as well).
Every factor influencing a crop can be controlled in a polytunnel. Polytunnels are often used in floriculture and plant nurseries, as the revenue value of the plants can justify the expense.
In recent years the true adaptability of polytunnel structures has been realised by adapting them to suit livestock housing. It is now commonplace in the UK to see polytunnels used for housing sheep, alpacas, goats, calves and poultry.
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 so as to automate 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 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 poly house 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 is an excellent example of Polyhouse farming taking place in a developing country.
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. [3]
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. [4]
Farmers in Iraq are building these in increasing number and adding drip irrigation to grow tomatoes. [5]
Vegetable farming is the growing of vegetables for human consumption. The practice probably started in several parts of the world over ten thousand years ago, with families growing vegetables for their own consumption or to trade locally. At first manual labour was used but in time livestock were domesticated and the ground could be turned by the plough. More recently, mechanisation has revolutionised vegetable farming with nearly all processes being able to be performed by machine. Specialist producers grow the particular crops that do well in their locality. New methods—such as aquaponics, raised beds and cultivation under glass—are used. Marketing can be done locally in farmer's markets, traditional markets or pick-your-own operations, or farmers can contract their whole crops to wholesalers, canners or retailers.
A greenhouse is a special structure that is designed to regulate the temperature and humidity of the environment inside. There are different types of greenhouses, but they all have large areas covered with transparent materials that let sunlight pass and block it as heat. The most common materials used in modern greenhouses for walls and roofs are rigid plastic made of polycarbonate, plastic film made of polyethylene, or glass panes. When the inside of a greenhouse is exposed to sunlight, the temperature increases, providing a sheltered environment for plants to grow even in cold weather.
Season extension in agriculture is any method that allows a crop to be grown beyond its normal outdoor growing season and harvesting time frame, or the extra time thus achieved. To extend the growing season into the colder months, one can use unheated techniques such as floating row covers, low tunnels, caterpillar tunnels, or hoophouses. However, even if colder temperatures are mitigated, most crops will stop growing when the days become shorter than 10 hours, and resume after winter as the daylight increases above 10 hours. A hothouse — a greenhouse which is heated and illuminated — creates an environment where plants are fooled into thinking it is their normal growing season. Though this is a form of season extension for the grower, it is not the usual meaning of the term.
A season is a division of the year marked by changes in weather, ecology, and the amount of daylight. The growing season is that portion of the year in which local conditions permit normal plant growth. While each plant or crop has a specific growing season that depends on its genetic adaptation, growing seasons can generally be grouped into macro-environmental classes.
A nursery is a place where plants are propagated and grown to a desired size. Mostly the plants concerned are for gardening, forestry, or conservation biology, rather than agriculture. They include retail nurseries, which sell to the general public; wholesale nurseries, which sell only to businesses such as other nurseries and commercial gardeners; and private nurseries, which supply the needs of institutions or private estates. Some will also work in plant breeding.
Dryland farming and dry farming encompass specific agricultural techniques for the non-irrigated cultivation of crops. Dryland farming is associated with drylands, areas characterized by a cool wet season followed by a warm dry season. They are also associated with arid conditions, areas prone to drought and those having scarce water resources.
Plastic mulch is a product used in plasticulture in a similar fashion to mulch, to suppress weeds and conserve water in crop production and landscaping. Certain plastic mulches also act as a barrier to keep methyl bromide, both a powerful fumigant and ozone depleter, in the soil. Crops grow through slits or holes in thin plastic sheeting. Plastic mulch is often used in conjunction with drip irrigation. Some research has been done using different colors of mulch to affect crop growth. Use of plastic mulch is predominant in large-scale vegetable growing, with millions of acres cultivated under plastic mulch worldwide each year.
A vivarium is an area, usually enclosed, for keeping and raising animals or plants for observation or research. Water-based vivaria may have open tops providing they are not connected to other water bodies. An animal enclosure is considered a vivarium only if it provides quality of life through naturalistic components such as ample living space and natural decor that allow and encourage natural behaviours. Often, a portion of the ecosystem for a particular species is simulated on a smaller scale, with controls for environmental conditions such as temperature, humidity and light.
Hardiness of plants describes their ability to survive adverse growing conditions. It is usually limited to discussions of climatic adversity. Thus a plant's ability to tolerate cold, heat, drought, flooding, or wind are typically considered measurements of hardiness. Hardiness of plants is defined by their native extent's geographic location: longitude, latitude and elevation. These attributes are often simplified to a hardiness zone. In temperate latitudes, the term most often describes resistance to cold, or "cold-hardiness", and is generally measured by the lowest temperature a plant can withstand.
In agriculture and gardening, a cold frame is a transparent-roofed enclosure, built low to the ground, used to protect plants from adverse weather, primarily excessive cold or wet. The transparent top admits sunlight and prevents heat escape via convection that would otherwise occur, particularly at night. Essentially, a cold frame functions as a miniature greenhouse to extend the growing season.
A hardiness zone is a geographic area defined as having a certain average annual minimum temperature, a factor relevant to the survival of many plants. In some systems other statistics are included in the calculations. The original and most widely used system, developed by the United States Department of Agriculture (USDA) as a rough guide for landscaping and gardening, defines 13 zones by long-term average annual extreme minimum temperatures. It has been adapted by and to other countries in various forms. A plant may be described as "hardy to zone 10": this means that the plant can withstand a minimum temperature of 30 to 40 °F.
In agriculture and gardening, row cover is any transparent or semi-transparent flexible material, like fabric or plastic sheeting, used as a protective covering for plants, usually vegetables. Covers are used to extend growing seasons, and reduce undesirable effects of cold, wind and insects. Row covers can reduce the drying effect of wind, and can provide a small amount of warming in a similar way to unheated cold frames, greenhouses and polytunnels, creating a microclimate for the plants.
Worldwide more human beings gain their livelihood from agriculture than any other endeavor; the majority are self-employed subsistence farmers living in the tropics. While growing food for local consumption is the core of tropical agriculture, cash crops are also included in the definition.
A root cellar, fruit cellar or earth cellar is a structure, usually underground or partially underground, used for storage of vegetables, fruits, nuts, or other foods. Its name reflects the traditional focus on root crops stored in an underground cellar, which is still often true; but the scope is wider, as a wide variety of foods can be stored for weeks to months, depending on the crop and conditions, and the structure may not always be underground.
Plasticulture is the practice of using plastic materials in agricultural applications. The plastic materials themselves are often and broadly referred to as "ag plastics". Plasticulture ag plastics include soil fumigation film, irrigation drip tape/tubing, plastic plant packaging cord, nursery pots and bales, but the term is most often used to describe all kinds of plastic plant/soil coverings. Such coverings range from plastic mulch film, row coverings, high and low tunnels (polytunnels), to plastic greenhouses.
Controlled-environment agriculture (CEA) -- which includes indoor agriculture (IA) and vertical farming—is a technology-based approach toward food production. The aim of CEA is to provide protection from the outdoor elements and maintain optimal growing conditions throughout the development of the crop. Production takes place within an enclosed growing structure such as a greenhouse or plant factory.
Soil steam sterilization is a farming technique that sterilizes soil with steam in open fields or greenhouses. Pests of plant cultures such as weeds, bacteria, fungi and viruses are killed through induced hot steam which causes vital cellular proteins to unfold. Biologically, the method is considered a partial disinfection. Important heat-resistant, spore-forming bacteria can survive and revitalize the soil after cooling down. Soil fatigue can be cured through the release of nutritive substances blocked within the soil. Steaming leads to a better starting position, quicker growth and strengthened resistance against plant disease and pests. Today, the application of hot steam is considered the best and most effective way to disinfect sick soil, potting soil and compost. It is being used as an alternative to bromomethane, whose production and use was curtailed by the Montreal Protocol. "Steam effectively kills pathogens by heating the soil to levels that cause protein coagulation or enzyme inactivation."
A seawater greenhouse is a greenhouse structure that enables the growth of crops and the production of fresh water in arid regions. Arid regions constitute about one third of the Earth's land area. Seawater greenhouse technology aims to mitigate issues such as global water scarcity, peak water and soil becoming salted. The system uses seawater and solar energy, and has a similar structure to the pad-and-fan greenhouse, but with additional evaporators and condensers. The seawater is pumped into the greenhouse to create a cool and humid environment, the optimal conditions for the cultivation of temperate crops. The freshwater is produced in a condensed state created by the solar desalination principle, which removes salt and impurities. Finally, the remaining humidified air is expelled from the greenhouse and used to improve growing conditions for outdoor plants.
Tomato grafting is a horticulture technique that has been utilized in Asia and Europe for greenhouse and high tunnel production and is gaining popularity in the United States. Typically, stock or rootstock are selected for their ability to resist infection by certain soilborne pathogens or their ability to increase vigor and fruit yield. The scion of the grafted tomato represents the upper portion of the plant and is selected for its fruit quality characteristics. There are several methods for grafting tomatoes and they have certain advantages and disadvantages. Once the grafts are made, the plants are moved into a chamber or environment with high relative humidity (>90%) and low light levels to reduce water stress in the scion while the graft union forms.
Climate-friendly gardening is a form of gardening that can reduce emissions of greenhouse gases from gardens and encourage the absorption of carbon dioxide by soils and plants in order to aid the reduction of global warming. To be a climate-friendly gardener means considering both what happens in a garden and the materials brought into it as well as the impact they have on land use and climate. It can also include garden features or activities in the garden that help to reduce greenhouse gas emissions through processes not directly related to gardening.