Raquele Mendes de Lira

Production, water consumption and nutrient content of Chinese cabbage grown hydroponically in brackish water

Underground water reserves in the semi-arid region of Brazil are stored in the crystal formations that in large part have high concentrations of salt. However, the scarcity of this resource makes the use of this water necessary for various activities, including agriculture. The aim of this study was to evaluate the use of brackish water on the electrical conductivity and pH of the nutrient solution, and on the production, water consumption and the uptake of nutrients in Chinese cabbage (Brassica pekinensis L.) under a hydroponic system. The experimental design was completely randomised, with four replications and six levels of water salinity (0.2, 1.2, 2.2, 3.2, 4.2 and 5.2 dS m-1), obtained by adding NaCl to the local water supply, with this water being used to prepare the nutrient solution and to make up the volume lost through evapotranspiration. The results showed that with the exception of the treatment at the lowest salinity, there was a tendency to increased electrical conductivity of the nutrient solution with the increasing salinity of the water; that the pH of the nutrient solution remained within the normal range throughout the cycle; that with the increasing salinity of the solution there was a reduction in all growth and production variables under analysis, in water consumption, and in leaf N, K, Ca and Mg, and an increase in leaf concentrations of Na and Cl. It is possible to use brackish water for the production of Chinese cabbage when grown hydroponically as an alternative for those producers who have an available supply of brackish water and a restricted supply of fresh water, however with a reduction in productivity.

NUTRIÇÃO MINERAL DE ALFACE AMERICANA EM CULTIVO HIDROPÔNICO COM ÁGUAS SALOBRAS

Water availability in the Brazilian semiarid is restricted and often the only water source available has high salt concentrations. Hydroponics allows using these waters for production of various crops, including vegetables, however, the water salinity can cause nutritional disorders. Thus, two experiments were conducted in a greenhouse at the Department of Agricultural Engineering of the Federal Rural University of Pernambuco, to evaluate the effects of salinity on the mineral nutrition of crisphead lettuce, cultivar Taina, in a hydroponic system (Nutrient Film Technique), using brackish water in the nutrient solution, which was prepared by adding NaCl to the local water (0.2 dS m). A randomized blocks experimental design was used in both experiments. The treatments consisted of water of different salinity levels (0.2, 1.2, 2.2, 3.2, 4.2 and 5.2 dS m) with four replications, totaling 24 plots for each experiment. The water added to compensate for the waterdepth loss due to evapotranspiration (WCET) was the brackish water of each treatment in Experiment I and the local water without modifications in Experiment II. The increase in the salinity of the water used for the nutrient solution preparation reduced the foliar phosphorus and potassium contents and increased the chloride and sodium contents, regardless of the WCET. Foliar nitrogen, calcium, magnesium and sulfur contents were not affected by increasing the water salinity used for the nutrient solution preparation.