Our objective was to determine which method of hydroponic production is best suited for growing salad mix. Optimizing salad mix production may be quite different than growing heads of lettuce for market. One big difference is that salad mix is sold by weight. In the first six weeks of operation of our polyculture system during the previous project we harvested 97 pounds of lettuce leaves from the 128 square feet of growing area. These leaves were blended with field grown lettuce and greens to make the final product. The field grown product seems to be heavier and more resistant to tearing and blemishing. This mix retails between $4.00 -$6.00 per pound depending on package size. In addition we harvested several pounds of hydroponic basil tops that were also used in our packaged salad mix. Roughly speaking this translates into about one dollar
per square foot per week of production in this seasonal period.

In the polyculture project the lettuce was grown using a tank based float system. The nutrient solution is constantly maintained at a depth of two inches in the growing tank and recirculates continuously. The crop is supported in net baskets placed in holes cut in a sheet of Styrofoam that floats on the nutrient solution=s surface. In this current project we compared the polyculture growing strategy with a nutrient film technique (NFT). The NFT system was designed and constructed as part of this project and will be detailed in this report.

Bio-cord technology is being used as a means of maintaining water quality in the closed polyculture system as part of our project. The cord is basically a core covered with many rings of thread that provides a large surface area for the attachment of microbes. In the first four weeks of operation of our hydroponic system, during the polyculture project, the pH values were found to fluctuate considerably and dropped quite rapidly. We tried to buffer this movement by adding ground limestone and crab shells which seemed to help reduce the fluctuations and rate of pH decline. However, as the Bio-Cord filter began to age and get covered with algae the system pH stabilized. We do not know if there is a correlation here and attempted to research this aspect of system operation. Biological filters may have a stabilizing affect on hydroponic systems. We attempted to study how the filter impacted nutrient consumption and balance. 

Temperature is very important in lettuce production. High greenhouse temperatures can be a problem. High electricity costs accrue since ventilation fans run almost continuously on sunny days to keep the
temperature down. We compared similar NFT hydroponic systems; one located in the greenhouse and one located outside the greenhouse. In Australia, 180 acres of hydroponic lettuce are grown outside on NFT gully tables with wind barriers and shade screen as the only protection. An outside table-based hydroponic system eliminates one of our biggest problems; weeding. During our project, compared to field growing, cut worms and root eating nematodes were eliminated as a concern; stem rots were minimized. Other problems surfaced, primarily wind related, as the project proceeded.

Statement of Objectives

                1. Operate two types of hydroponic production tables using float and NFT techniques in the greenhouse in a manner that the production can be compared. 

                2.  Design, set up, and operate a low cost NFT system outside the greenhouse that can be compared to a similar system located inside the greenhouse and
                field production.

                3. Utilize Bio-Cord filters in a controlled experiment in the greenhouse system to determine the product's impact on water quality maintenance

                4. Monitor and record production parameters including crop yields, environmental and economic data

                5. Write a report completely documenting the project's results.

Facilities

The tank system and one set of NFT gullies were installed in an existing 30' x 96' greenhouse on Coonamessett farm. The greenhouse is heated by a Seibring Model OT210 oil heater controlled by a Dayton single stage thermostat. Ventilation is provided by two 48-inch fans and two thermostatically controlled shutters. The greenhouse is covered with doubled poly and the floor consists of gravel. The water supply is from a well.