High Tunnel Agriculture
3. Northern Field Production of Leaf and Romaine Lettuce Using a High Tunnel. Rader. 2006. 6pp.
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A technical research article on using a high tunnel to grow greens, in this case, lettuces: a leaf lettuce called ‘Two Star’ and a romaine lettuce called ‘Parris Island Cos’. Conducted in 2005, this was a graduate project at the University of Alaska to test if high tunnels extended the season, yield, and size of a cool season crop throughout multiple harvests.
Lettuce plugs were propagated four weeks ahead of transfer to a high tunnel and field and were arranged into ten one-week interval planting dates. The high tunnel was a ClearSpan, two-bay high tunnel, covered in 6 mil polyethylene plastic with side and end walls opened for ventilation. The crops were fertilized, and 18 uniform transplants were planted in a randomized complete-block design 6x3 grid, and irrigated with drip tape. Plant height measurements were taken throughout growth and plants were harvested 6 weeks after planting with head weight, height, and position in plot recorded. Plot factors were high tunnel or open field followed by planting date and cultivar. The earliest plant date was July 4 and latest September 28.
Planting date had the greatest affect on yield and other variables but the high tunnel contributed significantly to head development in the Romaine lettuce. Overall, this study showed that these varieties of lettuce did not do better in the high tunnel environment; in fact, they performed much better outside. However, beside plant vigor there were other advantageous factors to consider - plants grown in the high tunnel required less time to clean and there was some protection from wind, heavy rain, and frost. Limitations of the study were that direct seeding may have more appropriate at different times in the season and the choice of species might not have worked well for mid-season production. Additionally, lettuce is a cool season crop and the overly warm environment of the high tunnel may not have been well suited to its life history.
The authors suggest further research into nutritional content and taste differences between field grown and high tunnel crops.