Hanna Y. Hanna, Coolman, Denise | 9/30/2006 12:31:06 AM
News Release Distributed 11/06/03
BOSSIER CITY – Growing tomatoes in a greenhouse may be less costly in the future.
Dr. H.Y. Hanna, an LSU AgCenter scientist working at the Red River Research Station in Bossier City, is studying how spacing between bags that hold the plants affects the amount of heat required to produce tomatoes in greenhouses.
"Direct heat application to the roots can transfer heat quicker to plant sap, and internal plant temperature can replace air temperature to determine heat requirements for the greenhouse," Hanna said.
"If the bags are placed close together in double rows – forming a pair of solid walls contacting heating tubes – we expect heat transfer to the roots will be more efficient," Hanna said. "I’m trying to find out the volume of the root medium to sustain one plant per bag and use 640 bags per greenhouse.
"In the traditional system, we use 320 bags with two plants each, but gaps between bags allow more heat to escape to the air."
The extra costs involved with doubling the number of bags include buying additional bags, which can run between $50 and $60 more per greenhouse.
"But if we can reduce heating costs, this cost will be absorbed in no time," Hanna said.
Heat is an important factor in growing greenhouse tomatoes, but heating greenhouses can be expensive, Hanna points out.
Greenhouse tomatoes normally are heated by hot air blown directly into plants’ surroundings from oil or gas furnaces, Hanna said. The houses also can be heated by circulating hot water through the interior of the greenhouse in pipes that release the heat to the plants’ environment.
But heating greenhouses by using forced air is more popular among growers because of simplicity and ease of maintenance of such a system, Hanna said.
Traditionally, furnaces that generate heated air are suspended as high as 10 feet above the greenhouse ground level to keep the heaters out of the workspace and to blow the heated air above the plant tops. In top-heated greenhouses, there can be temperature differences of up to 15 degrees F from the top to the bottom of plants, because warm air is lighter and stays at higher levels in the greenhouse.
Heating tubes connected to a heater and running through the plants is a good way to heat the tomato crop, Hanna said. Thermometers to monitor the temperature inside the plants and increase or decrease heater output to meet plant needs is a new way to save energy and enhance yield.
"From now on, the sap temperature will be used to tell the heaters when to come on and go off," Hanna said. "What matters is the temperature inside the plant, not the temperature of the air."
This study is a continuation of a study Hanna has been doing for several years that involves the direct application of heat to a plant’s root system.
For more information on how to grow greenhouse tomatoes, contact Hanna at (318) 741-7430. For even more general information on a range of topics, visit www.lsuagcenter.com.