Low Tunnel Strategies for Microclimate Modification and Early Vegetable Production
This study tested various perforated plastic materials (clear and white) used as low tunnels either alone or in combination with a spun-bond material for benefits including: frost protection, earliness in planting and harvesting, and season extension. The experiment consisted of six treatments: Four combinations of clear and white plastic with or without the spun-bond materials and two controls with no covers (normal planting date in May and early planting date in April). Using slicing cucumber and tomato, the low tunnels were investigated for their impact on the microclimate, crop earliness and economics. Our preliminary studies showed that by putting perforated clear plastic and spun-bond material together in a low tunnel system air temperature during frost events can be increased significantly inside the tunnels.
Objective 1. Develop and validate of new low tunnel technologies.
Objective 2. Conduct an economic analysis of the production systems.
Objective 3. Deliver information to growers and scientific community.
Data collection was completed from February 2011 – September 2011 and from February 2012- September 2012.
Tomato transplants were started in the greenhouse the end of February. The field experiment began on April 26, 2011 and April 24, 2012 with the planting of tomatoes and cucumbers and the installation of the low tunnels. Low tunnels were removed a month after installation. The final harvest of the tomatoes was on September 7, 2011 and August 29, 2012 and the final harvest of the cucumbers was August 12, 2011 and August 9, 2012.
The experiment was conducted in 2011 and 2012, followed by final data analysis and dissemination of results. Preliminary results to date are discussed below:
All low tunnel configurations provided 1-7 oF of frost protection compared to the no cover early planting date (NCE) treatment and resulted in significant heat accumulation at the beginning of the growing season. Frost damage in the NCE treatment was evident in the field, since frost damaged plants were set back compared to the covered plants. The low tunnel treatments for cucumber were first harvested on June 27, 2011, while the no cover normal (NCN) planting date treatment was first harvested on July 14, 2011. The cucumber clear dual layer (CDL) treatment had the greatest yield for the majority of the season; while the clear single layer (CSL) treatment was second highest. At the end of the season; however, there was no difference in total cumulative yield amongst treatments. This result confirmed that the main impact of the row covers was on earliness which may result in significant economic benefit to the grower.
The tomatoes in the low tunnel treatments were first harvested on July 19, 2011, while those in the NCN planting date treatment were first harvested on August 1, 2011. In 2011 tomato in the CSL treatment had the greatest yield for the entire season followed by the white single layer (WSL) treatment. At the end of the season the greatest difference for overall marketable yields was between the low tunnel treatments and the NCN planting date treatment.
Similar to 2011, all low tunnel configurations provided 1-7 oF of frost protection compared to the NCE treatment and resulted in significant heat accumulation at the beginning of the growing season. The only exception was during the April 28, 2012 frost event when the temperature was warmer in the no cover early planting date (NCE) treatment and cause significant frost damage to the dual and single layer treatments. This observation with lower temperature inside the tunnel than in the open field was unusual and is still under investigation. Other weather parameters like dew point, and wind speed may help explain this observation. The low tunnel treatments for cucumber were first harvested on June 25, 2012, while the NCN planting date treatment was not ready for harvest until July 9, 2012. During the 2012 season, yields in the NCN treatments were highest at the end of the season, because of the lack of protection during the unique frost event.
The tomatoes in the low tunnel treatments were first harvested on July 12, 2012, while those in the NCN planting date treatment were first harvested on July 23, 2012. In 2012 tomato in the WSL treatment had the greatest yield for the entire season followed by the CSL treatment. At the end of the season the greatest overall marketable yields was observed with CDL treatments.
The objective of this study was to determine the best low tunnel technology for microclimate modification and to allow growers to plant and harvest vegetables earlier, when prices are higher. The CDL treatments provided the most frost protection and significantly higher number of growing degree days compared to the other treatments. The low tunnel treatments were harvested almost 1-2 weeks earlier than the NC treatments planted at the normal planting date and yields during those two weeks commanded the highest market prices. An economic evaluation of the systems will be conducted at the end of the study.
Impacts and Contributions/Outcomes
To date, results from this project have been disseminated to the scientific and grower communities through presentations at the following Conferences:
2010 Great Lakes Fruit, Vegetable, and Farm Market Expo, Grand Rapids, MI
2011 Great Lakes Fruit, Vegetable, and Farm Market Expo, Grand Rapids, MI
2011 American Society of Horticultural Science (ASHS) Annual Meeting, Waikoloa, HI
2012 Great Lakes Vegetable Working Meeting, East Lansing, MI
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