Jim Wills, Gary Honea, Sam Ray, Mike Buschermohle, Allen Straw, Carl Sams

Two new thirty-foot by ninety-six foot plastic greenhouses were constructed on the Plant Sciences Unit of the Knoxville Experiment Station in the Spring and Summer of 2002. The houses were equipped with trellis support systems for growth of indeterminate varieties of greenhouse tomatoes. A crop of Trust variety tomatoes was grown in the fall and early winter to evaluate the production system and to evaluate a poly tube air-recirculation system for moving air from the upper portion of the house down into the plant canopy area to reduce energy costs and to increase yields during cooling and heating periods of growth during the season. On August 8, plants were put into three-gallon black plastic bags filled with perlite and fed water and plant nutrients via individual spray stakes at each bag.

The final harvest of the crop was on December 18. One house was used as a control house and the second house was used as a treatment house to compare the air recirculation system to an identical house without the air-recirculation system. All tomatoes were harvested, weighed, graded and counted from each house to evaluate yield, quality, size, taste (informal evaluations), and marketability. Energy costs for each house were recorded and compared at the end of the growing season to determine costs for each house.

Estimates are that over 600 plastic greenhouses are located in East Tennessee. For many years, these houses were used for tobacco transplant production. With the decline in tobacco and tobacco transplant production the last few years, many of theses houses have been idle. Owners of many of these houses have been searching for viable crops to put the houses back into production profitability. Our research entails growing and evaluating crop types and varieties that can be profitability grown in greenhouses that also have viable markets in the area. Greenhouse tomatoes have the potential to be one of the more profitable crops for greenhouse production and have adequate market potential at a time when field tomatoes are out of season. Reduction of energy costs for tomato production can significantly increase profit from each crop. A major expense in greenhouse production during the colder months of the year are electricity and heating fuel. Plastic houses require significant heating during cold periods due to the low insulating value of the plastic covers. During the warmer months of the year, significant energy costs are incurred cooling houses to keep temperatures below 85 degrees F. Temperatures hotter than 85 degrees F result in loss of fruit set, therefore lower yields.

A trellis system to support the tomato crop was installed in each house prior to planting crops. Treated posts 4" x 4" x 10' were used for trellis supports. Five rows of posts were installed lengthwise in each house to create rows 85' long and five feet apart. End posts were installed in augered holes with concrete poured around the first two and last two post in each row, the remaining post in each row were tamped with soil. Posts were spaced approximately 12 feet apart in the rows and rows were five feet apart. A 4" x 4" x 12' post was used as a brace at the ends of each row between the last two posts. The brace was bolted to each post at each end. Posts were installed three feet deep which left a post height of seven feet above ground. An eighteen inch length of treated 2" x 6" with a ½ " diameter hole one inch from each end and one inch down from the top of the post was bolted across the top of each to form a crossbar. High tensile fencing wire was threaded through the holes and stretched from one end of the row to the other end and attached to the eyebolt on the end of 6" x 48" screw-type anchors. The anchors were screwed into the ground two feet beyond each end post until only the eyebolt was left above ground. Each row of posts supported two wires and one anchor was used on the end of each row. High tensile fencing wire ratchets were installed in the wire at the end of the row and the wire was tensioned using the ratchets. Wire crimps were used to attach the wire at connection points. This system permits a double row of plants along each row of posts. Each greenhouse contained ten rows of tomato plants in double rows along each row of posts and wire.

Trust variety of tomatoes were planted in each greenhouse on August 8, 2002. Plants were approximately 8-10 inches tall at planting. 700 plants were put in each house in three-gallon black plastic bags filled with approximately 0.4 cubic feet of perlite ( a 4 cubic foot bag of perlite will fill approximately ten plant bags). A spray stake was inserted in each bag to supply water and dissolved nutrients to each plant. Nutrients were mixed with water in 55 gallon plastic barrels and injected into the bags with the spray stakes. Timing of injectors was controlled by a solar controller that measured incident sunlight on plants and injected water and nutrients based on amount of sunlight each day. A solar sensor connected to the controller and mounted in the top of the greenhouse above the plant canopy measured incident sunlight and activated the controller to regulate plant feeding. The solar

controller allows watering of the plants of the house in zones. Three Dosatron brand injectors which are powered by water pressure were used to meter water and nutrients into the lateral lines that supply each spray stake. This permits watering each double row of plants (140 plants) for a preset time and then moving to the next zone for continuation of the watering for each feed cycle. Electric solenoids are mounted in each main lateral line to 140 plants and opens when a signal from the solar controller indicates need for water and nutrients. The solenoid remains open for a preset time and feeding occurs while the solenoid is open. At the end of the feeding cycle for a given row, the solenoid closes and pauses a few seconds before cycling to the next row until all rows have received water and nutrients. The next feeding cycle occurs when sufficient sunlight has been received and the controller starts a new feeding cycle to all rows.

Nutrient mixes are determined by several factors including plant variety, plant size and minerals contained in the water supply. The pH of the water supply used was 7.2 and was adjusted to a pH of around 5.8 to 6.2, which is best for tomato growth and flavor. Nitric acid was used to lower the pH to the desired level. Acid was mixed with water in a 55 gallon plastic barrel and one Dosatron was used to meter this mixture into the flow of water and nutrients to the plants. The final pH was measured at the spray stake at the bag to assure a constant pH of about 5.8 to 6.2.

A second Dosatron was used to meter water from a 55 gallon plastic barrel containing magnesium sulfate and 4-18-38 tomato fertilizer. Based on water analysis, 10.5 pounds of magnesium sulfate and 25.5 pounds of 4-18-38 was needed in 40 gallons of water. A third Dosatron was used to meter water from a 55 gallon plastic barrel containing calcium nitrate and potassium nitrate mixed together. 22 pounds of calcium nitrate and 10.4 pounds of potassium nitrate in 40 gallons of water were required for the proper nutrient balance. These rates were for plants that had reached the first bloom on the fourth cluster to full growth. From transplant to first bloom on fourth cluster, a 50% rate of these nutrients was used. The amount of water with plant nutrients supplied to each plant on a daily basis varied from one liter at transplant to 2 to 2-1/2 liters at full growth.

The following table lists some of the major items needed to start a hydroponic greenhouse production program for crops such as tomatoes. A trellis support system and components are not listed individually, however, most 30' x 96' houses will require forty 4" x 4" x 10' treated posts for supports and ten 4" x 4" x 12' posts for end braces and 60 feet of 2" x 6".treated lumber for crossbars to support wire. About 900 feet of high tensile fencing wire, ten wire ratchets, and ten 6" x 48" screw anchors are needed in addition to the posts to construct the trellis and wire support system. Local prices at lumber supply yards and farm supply stores will run around $900 for these items including 20 bags of pre-mixed concrete to anchor the first two and last two posts of each row.

Some sources for items listed in the table below are shown at the end of the table for each item. These sources are by no means complete nor endorsed, but are merely listed to give a starting place for locating needed supplies.

Hydro-Gardens, Inc.

P.O.Box 25845

Colorado Springs, Colorado 80936-5845

Phone 800-634-6362

719-495-2266

web

Sonne-Gro

7141 Old Rutledge Pike

Knoxville, TN 37924

Phone 865-546-9608 or 800-766347

Rain-Flo Irrigation, LLC

884 Center Church Road

East Earl, PA 17519

Phone 717-445-6976

The air-recirculation system pulls warmer air from the upper regions of the greenhouse and circulates the air along each row via poly tubes running lengthwise down the rows horizontally about 36 inches above the ground. Poly tubes have holes punched in the tube sized and spaced to achieve a uniform discharge and match the air volume output of the blowers used on each row. Tubes are mounted in the center of the double rows and are supported by eyebolts or spikes in the side of the posts supporting a high tensile wire running the length of the row and secured to the end post on each double-row. Blowers are mounted on the end posts of each row with plywood mounts and U-bolts clamped around the post.

A fall crop of tomatoes was grown in two adjacent greenhouses at the Plant Sciences Unit of the Knoxville Experiment Station in the Fall of 2002. One house was equipped with the air-recirculation system and one house was not equipped with the system. The main purpose of the research was to evaluate the air-recirculation system with respect to possible increased yields and quality of tomatoes and possible reduction in overall energy costs to produce a tomato crop. Each house was heated with two 150,000 btu propane dual combustion chamber heaters. Each house was cooled with two 42 inch fans, one 24 inch fan and a five foot by twenty four foot Carolina Cooler which circulated water through

paper media via a recirculating pump. Electrical costs in the house with the air-recirculation system was $452.49 from August 8 to December 18. Electrical costs in the house without the air-recirculation system was $222.89 from August 8 to December 18. The difference in electrical costs between the two houses was the cost to run the air-recirculation system which was $229.60. Propane heating costs in the house with the air-recirculation system was$1,364.02 while propane cost in the other house was $1,499.91, a difference of $135.89. Total energy cost for the air-recirculation house was $1,816.51 while total cost for the house without the air-recirculation system was $1,722.80. At one dollar per pound wholesale for tomatoes, less than 100 pounds of extra yield would pay for the energy cost difference. When adding a pro-rated cost for the blower system of $75 per crop ($150 per year), the total extra cost of the system including electricity is about $170 per crop. Earlier research in producer owned greenhouses have shown yield increases as much as 1,000 to 2,500 pounds of tomatoes per crop.

In addition to energy savings with the air-recirculation system, plants tend to stay dry and have lower incidence of disease caused by excess moisture. Powdery mildew and Botrytis flourish in very moist conditions which are greatly reduced with the air-recirculation system. Early day working conditions are improved in the greenhouse due to dryer plants. Operations such as suckering, clipping, pruning and similar activities are improved with dry plants and have less potential for disease to enter fresh wounds from sucker removal and pruning.

The spring crop and fall crop of 2003 will be thoroughly evaluated with respect to per- plant yields and fruit size and quality. This data will be reported in the next annual report of the vegetable initiative or you can get information in a more timely manner from the vegetable initiative web site at www. utvegetables.org

Email all comments and suggestions to ghonea@utk.edu
Copyright © 1999 by The University of Tennessee. All rights reserved.

This research represents one season's data and does not constitute recommendations.  After sufficient data is collected over the appropriate number of seasons, final recommendations will be made through research and extension publications.