High tunnel crop production systems capitalize on the greenhouse effect and its subsequent microclimate modification. They are part of controlled environment agriculture (CEA) systems for crop production. They can provide daytime air and soil warming during the spring, fall, and winter, and protection from heavy rains, strong winds, and other adverse weather conditions. Many producers in mild winter climates use high tunnels for cool season vegetables. As a production system, they offer dependable and specific crop production goals, including enhanced quality, increased yields, and improved timing, leading to improved product marketability and greater profits. They are labor intensive, even more than field production of vegetable crops. However, they are more than simply field production inside a structure and a cover, even though they typically produce crops that are gown in the soil. Their use can provide locally grown produce, limited or no pesticides use, and reduced transport distance to market. Crops can range from a polyculture of unique mixes of specialty products, or a monoculture of seedling transplants for field production, in, for example, lettuce (Lactuca sativa) transplants. They have an important, multifaceted role in the food production industry.
Unlike high-technology greenhouses of greater complexity and costs, high tunnels do have significant limitations for controlling the plant environment. They cannot control the root zone and the aerial zone of the plant as well as a greenhouse with climate control systems for heating, cooling, shading, etc. However, they do offer improved crop protection from adverse weather conditions compared with the open field or plasticulture techniques such as row (low) tunnels in the field. For example, the aerial environment is provided with rain and wind shelter, with limited insect exclusion, and with some protection from cold night air temperature. The root-zone environment is provided with a controlled water regime and the potential for nutrient enhancement.
The definition of a high tunnel is a freestanding or gutter-connected covered structure, without heating or electrical power, using passive ventilation for air exchange and cooling, and an irrigation system for crop production. They are modular in design, typically constructed of a curved metal pipe or steel tube frame with input/output from the ends or sides for worker and/or small tractor entry for soil tillage. They are considered temporary agricultural structures in terms of building codes, and can be easily covered each season and uncovered after the last harvest. They can be disassembled to be reconstructed at a different site in subsequent years. However, for a more permanent structure, concrete footings can be used in the construction.
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