In this experiment we evaluated the production, accumulation of nitrate, content and exportable mineral nutrient (N, P, K, Ca, Mg e S) of lettuce cultivars Regina and Verônica cultivated under two thermo-reflective screens (Aluminet®30%-O and Aluminet®40%-O), and a diffusive screen (ChromatiNet Difusor®30%). The trial was carried out in Viçosa, Minas Gerais State, Brazil. Seeds were sown in trays of 200 cells, under protected atmosphere, on 05/31/02. The transplant was accomplished on 06/26/02 and the harvest on 08/06/02, when the evaluations were performed. The thermo-reflective and diffusive screens were installed in structures type 'shut rectangular fence', with 2 x 4 x 36 m (height, width and length), close to the cultivation under open sky (control). We evaluated the production of mass, content of nitrate, content and exportable mineral nutrient (N, P, K, Ca, Mg e S). 'Regina' presented more tender leaves than the 'Verônica', therefore being more appropriate to the high quality demanding markets, even so, with larger content of nitrate. Considering the quantitative and qualitative aspects, the Aluminet®40% and ChromatiNet Difusor®30% screens should be recommended; though, the nitrogen should be adjusted to avoid the accumulation of nitrate. The growing conditions and cultivars influenced content and exportable mineral nutrients. With relation to the export of nutrients the following order was observed: K>N>Ca>P>Mg>S.
