RESEARCHES ON HIGH QUALITY HYDROPONIC LETTUCE PRODUCTION THROUGHOUT THE YEAR
Project no. 336 · Status: Kapanmış · 2016
Summary
In this experiment carried out in an unheated plastic tunnel in Izmir, possibilities of using floating system for iceberg lettuce production were investigated. Three different salinity levels (EC1, EC2 and EC3) were compared, 8.76 and 17.52 mM NaCl was added for EC2 and EC3, respectively into the nutrient solution used as control (EC1). NaCl application was started when leaves and roots of the plants began to develop, and continued up to harvest. Temperatures of greenhouse air and nutrient solution, changes in EC and pH of nutrient solution, head weight, nitrate content of the leaves, consumption of nutrient solution, and element contents of the leaves were determined. Trial repeated in four different periods: (Exp. 1) from December 16 to March 13, (Exp. 2) from March 24 to May 2, (Exp. 3) from May 18 to June 28 and (Exp. 4) from February 8 to March 29. Average temperatures of the nutrient solution varied between 9-19?C in the Exp. 1, 20-23?C in the Exp. 2, 27-35?C in the Exp. 3 and 16-22°C in the Exp.4. Plants were grown successfully during the first two and fourth trials; on the other hand, all plants died 41 days after transplanting due to the high temperatures in Exp. 3. Growing season lasted 87, 39 and 49 days in Exp. 1, 2 and 4, respectively. In the first trial, head weight changed according to salinity of nutrient solution, and the highest value (464 g) was obtained at EC2 compared to EC3 (419 g) and EC1 (438 g). There were no significant differences between EC levels of nutrient solution in respect to head weight in the second and fourth trials. Nitrate content of the leaves decreased by increasing EC of nutrient solution. Obtained results showed that floating system could be used for the production of iceberg lettuce in unheated greenhouses. However, the average temperature of the nutrient solution exceeding 30°C may limit the use of this method in summer. The salinity stress created by the addition of NaCl to the nutrient solution can be used to enhance the quality (e.g., reducing the nitrate content of plants) without significant losses of yield.