Effects of added chlorides and their concentrations on growth and nitrate content in leaf lettuce(Lactuca sativa L.) in hydroponics.

Nitrate in edible vegetables is converted to nitrite by nitrate reductase(NR) and/or bacteria in intestines. Nitrite and amine, in the intestine of some animals and human, bind to form nitrosamine, which is toxic and known as carcinogen. This study was carried out to examine the effect of added chlorides and their concentrations on growth, yield and nitrate content in leaf lettuce plants in hydroponics. Seeds of lettuce cv. “Samsunjokchukmyon” were planted on April 29, and seedlings were planted on June 2, and were cultured until July 5 in 1998. KCl and CaCl2 were used as chloride source and their concentrations were 1, 2 and 4 me/L, respectively, in the lettuce standard nutrient solution for National Horticultural Research Institute(NHRI). Completely randomized design with 3 replications was used. Nitrate content and NR activity were measured 2 and 5 weeks after planting(WAP). The obtained results were summarized as the follows: Leaf weight per plant was difference from harvest dates and treatments, but total leaf weight was not significantly different among treatments. Number of leaves was higher in KCI 2 me/L, CaCl2 1 me/L and control at 2 WAP than the others, and was higher in KCI 1 me/L, and control at 3 WAP than others, and was higher in control at 5 WAP. Total number of harvested leaves was the highest in control with 14, which followed by KCI 2 me/L and CaCl2 1 me/L. Nitrate content was decreased by addition of chloride in nutrient solution. Nitrate content in the 3rd and 9th leaves was significantly decreased. NR activity was higher in control and CaCl2 addition treatments, while KCl addition treatments reduced NR activity. However, no direct relationship with nitrate was observed. Growth characteristics such leaf length and leaf width were not significantly influenced by chloride addition.