Lettuce growth, yield and nitrate content as affected by electrical conductivity of nutrient solution.

Two lettuce cultivars, 'Alisia' and 'Tibet', belonging to Lactuca sativa L. var. longifolia (Lam.) Janchen and var. capitata (L.) Janchen, respectively, were grown in an open soilless system to evaluate the influence of three nutrient solution EC levels (1.5-2.5 and 3.5 dS/m), on growth, yield and quality. Plants were grown in greenhouse in pots filled with a mixture of peat and pumice (1:4-v:v). Solution was distributed by drippers. In both cultivars leaf area increased with time, but whilst in 'Tibet' no differences were observed among EC levels, in 'Alisia', as the EC was higher, leaf area increasing rate was lower. In the same period, fresh weight of both cultivars rose linearly and it was higher at the lower levels of EC. Compared with 'Tibet', 'Alisia' showed higher leaf area, fresh weight and dry matter content by 33, 38 and 17%, respectively. The highest nitrate head content was observed with 2.5 dS/m.