ABSTRACT
A research and development project was undertaken to compare several variations in hydroponic growing strategies. The primary crop utilized was salad mix; a blend of various types of lettuces and greens made by harvesting only the largest leaves of the plants. Additional crops included herbs and squash. The two primary growing systems utilized were a tank system, referred to as a flooded basin technique, and a gully system using the nutrient film technique. Two tank systems and one gully system were located inside a greenhouse and two gully systems were located outside that greenhouse. One tank system and the greenhouse gully system were on the same recirculating loop thus had the same nutrient supply. A number of comparisons were made on crop production and yield of the various systems.

INTRODUCTION

Coonamessett Farm is a twenty acre farming and research enterprise located on Cape Cod. Crops include small fruit, vegetables, bedding plants, and flowers. Research and technical consulting services are offered in small scale agriculture, aquaculture, and fisheries. In 1997, Coonamessett Farm received funding under the Ag-Tech program to develop a polyculture system utilizing tanks that could be used for greenhouse production of either plants or aquatic animal crops. We now have this tank based system in place and fully operational. As part of the polyculture project we monitored the system and collected data on the hydroponic production of salad mix. Salad mix production includes lettuce, greens, herbs, and edible flowers. The polyculture system worked extremely well. The current project, reported here, continued to utilize the tank based polyculture system, to compare with gully systems, in order to evaluate hydroponic growing strategies for salad mix both in and outside of greenhouse structures. 

Production of bags of pre-washed salad mix is a $1 billion industry nationwide with 600 million bags being sold last year. Ten million bags were sold in Boston in 1997; a 7 percent rise in sales compared to the previous year. Freshness is now being recognized as the key to the nutritional value of salad mix thus there is a growing opportunity for local producers to compete with the large western growers that currently dominate the market. Product variations are also of interest to chefs. Our work to date indicates that low cost hydroponic systems for salad mix may be a viable production alternative. Hydroponic systems are significant from an environmental perspective because the systems recycle water and contain the fertilizer.

Coonamessett Farm produces salad mix bags in two sizes; 8 oz for individual consumers and a 5 pound restaurant pack. We find an almost unlimited demand from restaurants during summer months on the Cape for our product as long as we meet the market price which is dictated by what comes off the plane from California; currently $4 per pound delivered. The restaurants prefer our mix because it contains the blend they desire and has a long shelf life due to its freshness. Our mix contains primarily larger leaves of lettuce and greens; it is not the typical Ababy@ mesclun mix. The demand for our individual bags is overwhelming during the summer as well. The 8 oz bags contain lettuce, greens, herbs, and edible flowers. The bags wholesale at $36/dozen and retail for $3.99 each. The high amount of labor to make these bags has limited our expansion into this market at present. 

We have experimented with all types of strategies to grow the salad mix in the field and in the greenhouse in order to reduce production costs. The Ag-Tech funded polyculture system has now provided us the means to investigate further improvements in growing the crops hydroponically. Crops grown hydroponically use water and nutrients more efficiently. They can be planted at higher densities and grow faster than in soil culture. The more controlled environment reduces the need for pesticides compared to field conditions. From an environmental standpoint hydroponic recirculating systems completely eliminate chemical runoff (no groundwater pollution with salts).