Materials and Methods:
The second year of a two year study focused on one heirloom tomato variety, Brandywine, and a one purple sweet pepper. All plants were grown according to USDA National Organic Standards in soil under a 30 by 90 foot high tunnel at the May Farm, Marine on St. Croix, MN. In the fall of 2006 chickens were grazed in the hoop and an early crop of salad greens were produced in the spring of 2007 by the farmer. The high tunnel was divided into 7 long rows. Counting from the north rows 2 and 3 were used for pepper production and rows 5 and 6 were used for tomato production. Row one was left empty, row 4 was planted in basil, and row 7 in German giant tomatoes. All water was supplied by drip irrigation tape buried 3 to 4 inches. Plants were mulched with 8 inches of straw to control weeds. A fish emulsion fertilizer applied at transplant. No other fertility of pest control was applied. Irrigation water was supplied from an on-site well that delivered water that varied in oxygen concentration from 4% of saturation to 20% of saturation during the growing season. The irrigation stream was divided as it entered the hoop house. Half of the water was oxygenated to150% to 180% of saturation using two flow-through electrolysis units at a flow rate of 0.5 gallon per minute per unit. Control water was passed through equivalent lengths of tubing directly beside the oxygenation units. Water was then directed to drip tapes laid in a grid to provide eight blocks of treated and non-treated experimental units per vegetable variety. Each block consisted of 5 plants spaced at 16 -18 inches within the row and 4 feet between rows. The center three plants from each block were harvested and all fruit counted and weighed throughout the growing season. Tomato plants were trellised on strings attached to the high tunnel super-structure. Irrigation was applied per the wishes of the farmer to optimize performance. Plants were deemed adequately water and did not show signs of stress during the growing season. A windstorm the first week in August blew the plastic off the high-tunnel. The plants were exposed to the elements for 8 days before the plastic could be replaced. Fortunately, it did not rain during that time. The farmer was very pleased with the quality of the plant growth, and with the fruit quality and yield.
The 2007 oxygenators were a significant improvement over the 2006 models. Units were easy to install and maintain, desired flow rates were easily achieved with eye level mechanical flow regulators/meters. In 2006 the oxygenators suffered from significant accumulation of precipitates on the electrodes that degraded performance and required time consuming maintenance. New for 2007 was a voltage switching the devise that switched the polarity of direct current applied to the electrodes every 24 hours. This prevented electrode contamination and produced 150 to 180% oxygen throughout the growing season.
The oxygenators also increased the irrigation water several degrees and decreased the EC compared to the control water. The effect of either of these changes in water supply on plant growth are unknown, but were not negative in this experiment.
Plant Performance and Yield:
The first season using flow through oxygenators to increase the dissolved oxygen in drip irrigation water provided extremely useful information on both plant and equipment performance. The equipment was adequate to supply a 30 by 90 foot greenhouse with oxygenated water. Increased maintenance convenience and better ergonomics will produce a farm friendly technique for increasing the oxygen content of drip irrigated water. Although experimental and production issues resulted in a loss of statistical significance, the trends in plant performance were positive with increased yields in bell pepper and tomatoes and increased fruit size in peppers.