Content of inorganic solutes in lettuce grown with brackish water in different hydroponic systems/ Teor de solutos inorganicos em alface cultivada com agua salobra em diferentes sistemas hidroponicos

The objective of this study was to evaluate the growth and accumulation of ions in lettuce grown in different hydroponic systems and recirculation frequencies. The experimental design was randomized blocks with 8 treatments and 4 replicates. The evaluated hydroponic systems were Nutrient Flow Technique (NFT) and an adapted Deep Flow Technique (DFT), the latter with recirculation frequencies of 0.25, 2 and 4 h. Both systems used fresh water and brackish water. Plant growth, accumulation of inorganic solutes ([Na.sup.+], [K.sup.+], [Cl.sup.-] and N[O.sup.-.sub.3]) and the correlation between dry matter production and [Na.sup.+]/[K.sup.+] and [Cl.sup.-]/ N[O.sup.-.sub.3] were evaluated. The salinity of the water used to prepare the nutrient solution caused decrease in growth and [K.sup.+] and N[O.sup.-.sub.3] levels, and increased contents of [Na.sup.+] and [Cl.sup.-] in the plants. When using fresh water the highest dry matter production was obtained in the NFT system. In case of brackish water the adapted DFT system increased the production, in relation to NFT system (at same recirculation frequency: 0.25 h). It was found that the choice of the type of hydroponic system and recirculation interval for the cultivation of lettuce depends on the quality of the water used to prepare the nutrient solution. Key words: soilless cultivation Lactuca sativa salinity NFT and DFT systems Objetivou-se, neste trabalho, avaliar o crescimento e o acumulo de ions em alface cultivada em diferentes sistemas hidroponicos e frequencias de recirculacao. O delineamento experimental foi o aleatorizado em blocos com 8 tratamentos e 4 repeticoes. Os sistemas hidroponicos avaliados foram a Tecnica do Fluxo Laminar de Nutrientes (NFT) e a Tecnica do Fluxo Profundo (DFT) adaptada, este ultimo com frequencias de recirculacao de 0,25, 2 e 4 h. Foi utilizada, em ambos os sistemas, agua doce e agua salobra. Foram avaliados o crescimento, o acumulo de solutos inorganicos ([Na.sup.+], [K.sup.+], [Cl.sup.-] e N[O.sup.-.sub.3]) e a correlacao entre a producao de materia seca e a relacao [Na.sup.+]/[K.sup.+] e [Cl.sup.-]/N[O.sup.-.sub.3]. A salinidade da agua utilizada no preparo da solucao nutritiva proporcionou diminuicao no crescimento e nos teores de [K.sup.+] e N[O.sup.-.sub.3] e aumentou os teores de [Na.sup.+] e [Cl.sup.-] nas plantas. Quando foi empregada agua doce, o sistema NFT proporcionou maior producao de massa de materia seca. No caso de agua salobra o sistema DFT adaptado aumentou