Productivity and salt tolerance of lettuce and rocket in different hydroponic systems with brackish waters

Abstract

In hydroponic systems, plants exhibit greater salt stress tolerance compared to other cultivation methods. However, this response can be further optimized through brackish waters management strategies and the selection of the most suitable hydroponic system. In this sense, the aim of this study was to evaluate the water productivity and salt stress tolerance of lettuce and rocket in hydroponic systems (floating, NFT – nutrient film technique, and vertical aeroponics) using nutrient solutions with different levels of salinity (2.0 – control, 3.7, 5.4, and 7.1 dS m^-1). In the lettuce experiment, plants were subjected to salt stress for a period of 25 days, whereas in the rocket cultivation, stress exposure was maintained for 20 days. Number of leaves, shoot fresh matter (SFM), shoot dry matter (SDM), productivity per area of SFM, relative productivity of SDM, water consumption, and water productivity were evaluated. Overall, salt stress showed no significant effect on crop performance in aeroponic cultivation for either species. Under increasing salinity conditions, both crops exhibited significant reductions in SFM, SDM, and productivity in NFT and floating systems. The salinity thresholds for production without significant losses were slightly better in floating system (3.06 and 3.70 dS m^-1 for lettuce and rocket, respectively) than in NFT hydroponics (2.52 and 1.44 dS m^-1 for lettuce and rocket, respectively). In aeroponics it was not possible to establish a threshold, since productivity did not decrease at the salinity levels tested. These results highlight the potential of aeroponics to optimize lettuce and rocket growth when cultivated using nutrient solutions prepared with high-salinity water.