Parâmetros de crescimento, concentração de nitrato, aspectos sensoriais e custos de produção de alfaces hidropônicas a partir do uso do concentrado de sistemas de dessalinização.

Abstract

The process of desalination of brackish water has been one of the alternatives for obtaining potable water to benefit the diffuse communities in the semi-arid region. Two desalination systems for potable water production were implemented: one in the community of Uruçu in the city of São João do Carirí and another in the School Macário Zulmiro in the district of Santa Luzia in the city of Picuí, both in the state of Paraíba. The utilization of the concentrates generated during the desalination process of the systems were studied for lettuce production through hydroponic laminar flow systems of nutrients. The objective of this work was to evaluate growth parameters, nitrate levels, sensory aspects and production costs of hydroponic lettuce using concentrate. Experiments were performed from the concentrate (1) with treatments levels of (0.1; 2.3; 4.4; 6.2 and 8.4) mS.cm-1 and with the concentrate (2), in the (0.1, 1.1, 2.1, 3.1 and 4.1) mS.cm-1 levels for the cultivation of crisp "crocante" and american "gloriosa" lettuce. The experimental design was completely randomized, with three replicates. It was observed that the development of the two lettuces studied depended on the electrical conductivity levels of each concentrate. The water consumption of the plants was reduced by 7.53% and 8.89% for crisp and American lettuce cultivated with concentrate (1) and 1.60% and 4.03 for concentrate (2), per unit increment of conductivity respectively. It was observed with the results of the growth parameters that the crispy lettuce presented higher tolerance to the excess salts of the concentrate when cultivated with the treatments of the concentrate (1), mainly in the treatments 6,2 and 8,4 mS.cm-1, Observed by linear reductions of leaf number, fresh shoot mass, shoot dry mass, moisture, dry mass of roots, stem mass and leaf area. The reductions of the growth parameters were lower when using the concentrate (2) and the two types of lettuce were tolerant to the levels of the treatments. Regarding the nitrate concentrations, results ranging from 694.5 to 982.0 mg.kg-1 were found in crisp and american lettuce, which are in agree with the maximum permissible value (3,500 mg.kg-1) of the regulation European seed 1881/2006 and american lettuce accumulated more nitrate than crisp. In the experiments with concentrate (1), the attributes color, flavor, crispness and overall impression were affected with the excess salts in the experiments with American lettuce, while for crisp lettuce, the color, flavor and overall impression were affected. When using the concentrate (2), no parameter was affected for the experiment with crisp lettuce. The purchase preference was above 90% for the crisp lettuce grown with the concentrate (2). The results of the cost estimates showed an investment of R$ 114,663.00 in the implementation of hydroponic and desalination systems, return on investment in approximately four years, lettuce production costs of R$ 0.30 per plant and costs for water production of R$ 1.47 per m³.