Abstract
ABSTRACT The production of vegetables in communities of family farmers in semiarid regions is limited due to rudimentary cultivation practices and systems, water scarcity, and excess salts in the water and soil. Thus, the objective of this work was to evaluate the production of rocket (Eruca sativa L. cv. Folha Larga) in a low cost hydroponic system, considering strategies for the use of brackish water in the nutrient solution. The experiments were conducted in complete randomized designs, in 6×2 factorial arrangements, with five replications, using rocket plants grown in different nutrient solutions, consisting of six salinity levels (1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 dS m -1) and two circulation frequencies of the nutrient solution (twice a day, at 8:00h, and 16:00h; and three times a day, at 8:00h, 12:00h, and 16:00h). In Experiment I, the nutrient solution lost by evapotranspiration was replenished with the respective brackish water used in its preparation; and in Experiment II it was replenished with public water (0.12 dS m -1). The shoot and root fresh and dry biomass of the plants and their respective dry weight proportions, and biometric variables were evaluated. Replenishing of the nutrient solution with public water resulted in lower losses in biomass and plant growth. The increases in circulation frequency of the nutrient solution did not affect the biometric variables, however, the plants prioritized shoot biomass development to the detriment of the root when using high circulation frequencies.
Highlights
The Brazilian semiarid region has low and irregular precipitation, and high evapotranspiration rate, which result in a negative water balance
The nutrient solution was prepared in twelve tanks filled with 90 L of public water; the amount of NaCl solubilized to reach the salinity rates was calculated based on the empirical equation of Richards (1954); and the fertilizer rates proposed by Furlani et al (1999) were used in all treatments
The variation of the pH of the nutrient solutions was lower than 15%, regardless of the electric conductivity of the nutrient solution (ECs) and circulation frequency of the nutrient solution
Summary
The Brazilian semiarid region has low and irregular precipitation, and high evapotranspiration rate, which result in a negative water balance. Several studies report the use of hydroponic systems as an alternative for this problem, since they allow the use of brackish water in the nutrient solution, require small areas for implementation, and present several other advantages (SANTOS JÚNIOR et al, 2014; SANTOS JÚNIOR et al, 2015; SILVA et al, 2016; NUNES et al, 2013; SANTOS et al, 2016). These benefits are due to the energy reordering caused by the minimization of the water matrix potential, making the energy required for water absorption by the plant reduce, practically, to the osmotic potential (SANTOS JÚNIOR et al, 2016). Proper management strategies for the preparation of nutrient solutions using brackish water can mitigate the effect of salinity on plants; and increasing the circulation frequency of the nutrient solution can provide greater oxygenation and solubilization of its nutrients (SOARES et al, 2010)
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