The influence of different quantities of nitrogen in the nutrient solution on growth, development and nitrate content was studied in aeroponically grown lettuce (Lactuca sativa L.). Three successive experiments were conducted in 1999 from April to September, in an aeroponic system. The lettuce plants, cv. Vanity, were grown in aeroponics using four different amounts of nitrogen in the nutrient solutions. The pH level was maintained between 5.5 and 6.5, and the EC between 1.8 and 2.2 mS/cm. Fresh weight measurements were made on all the material. The differences between the mean fresh shoot weights were statistically significant in all three experiments. In the first experiment, the maximum final fresh weight in the treatment with 8 mM nitrogen averaged 999.0 g. In the second and third experiments the largest amount of nitrogen, 12 mM NO3-N, significantly (p<0.05) increased the fresh shoot weight of lettuce plants. low levels of nitrate in the nutrient solution (4 mM NO3-N in the first and 1.2 mM NO3-N in the second aeroponic experiment) significantly (p<0.05) increased the fresh weight of the final roots compared with the level of nitrate in standard nutrient solution (12 mM NO3-N). The differences between the means for plant height were statistically significant (p<0.05) in all three experiments. In the first and third experiments the lengths of the primary roots of the lettuce plants were significantly (p<0.05) influenced by different NO3-N concentrations in the nutrient solution. The highest NO3- concentration in the lettuce leaves was recorded in plants grown in nutrient solutions with the highest NO3-N concentration (17 mM in the first, 12 mM in the second and third experiments). An acceptably low NO3- concentration was found in the leaves of lettuce treated containing with nutrient solution 4 mM NO3-N in all three experiments.
The quality of tomato fruits (Lycopersicon lycopersicum Mill.) depends on factors such as production conditions, the chosen cultivar, fertilisation, plant density, etc. The quality of tomato fruits cv. ‚Arletta™ grown on aeroponics has been analysed. The influence of plant density and pruning on yield quantity and quality was measured. Quality components were determined by high performance liquid chromatography (HPLC). The contents of sugars (sucrose, glucose, fructose and xylose) and organic acids (citric, malic, shikimic and fumaric acid) were analysed separately with regard to different plant density & 12, 16, 20 and 24 plants m &2 production surface. Evaluations showed that the differences in tomato quality, regarding the sugar (sucrose 0.46 g kg &1, glucose 14.31 g kg &1, fructose 12.06 g kg &1, xylose 0.27 g kg &1) and acid content (citric 7.79 g kg &1, malic 0.68 g kg &1, shikimic 4.36 g kg &1, fumaric 14.34 g kg &1) are not significant statistically with regard to plant density.