The yield, nitrate concentration and nutritional status of the lettuce cvs. Regina, Babá de Verão and Great Lakes cultivated in hydroponic system were evaluated. The experiment was carried out in fall from March to June/99 in a greenhouse of the Universidade Federal de Viçosa, Brazil. Two groups of nutrient sources were evaluated to compose the nutritive solutions. The solutions were composed of 13.6; 1; 7; 4.48; and 2.5 mmol L-1 of N, P, K, Ca and Mg, respectively. The sulfur contents were 3.5 or 2.5 mmol L-1 and micronutrient contents were 45; 32; 46; 2; 0.9; and 0.2 mmol L-1 of Fe, Mn, B, Zn, Cu and Mo, respectively. The solution 1 supplied 21,9% of N-NH4+, and the solution 2, 100% of N-NO3. The phosphorus sources employed were NH4H2PO4 and KH2PO4 for the solutions 1 and 2, respectively, and this variation implied in the use of different amounts of KCl in the solutions, providing different concentrations of Cl of 6.76 and 2.18 mmol L-1 for the solutions 1 and 2, respectively. Lettuce plants were grown in plastic recipient with 8 L of capacity. The recipients containing three plants were arranged to obtain spacing of 0.22 m between plants. A randomized block design in a 2 x 3 (solutions x cultivars) factorial scheme, with six replications and three plants per plot was used. The fresh matter of shoots, leaves, roots and stems, number of leaves, stem length, leaves dry matter and plant nutricional status were evaluated. The yield of cv. Regina was 233 g plant-1 and of cv. Babá de Verão was 193 g plant-1. The cv. Great Lakes presented low yield. The solution 1 provided smaller nitrate concentrations for Great Lakes (1082 mg kg-1 in fresh matter) and Regina (1092 mg kg-1 in fresh matter). The plants presented high concentrations of Mn, but without toxic symptoms. The plant nutritional status was satisfactory.
Lactuca sativa L.; nutritive solutions; mineral nutrition; soilless culture
