Abstract
ABSTRACT Cultivation using brackish waters can result in nutritional and metabolic imbalances in several plant species, consequently reducing the production of dry matter (DM) and accumulation of toxic ions (Na+ and/or Cl-) in plants. We evaluated the DM production, and nutrient and inorganic solute (Na+ and Cl-) content in green onion plants (cv. Todo Ano Evergreen - Nebuka) under different levels of nutrient solution salinity in combination with circulation frequencies of this solution. Two experiments were conducted in a hydroponic system, using a completely randomized design, in a 6 × 2 factorial scheme, with five replicates: six levels of nutrient solution salinity (1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 dS m-1) and two solution circulation frequencies (twice and thrice a day). In Experiment I, the evapotranspired depth was replaced using brackish water that was used to prepare each of the salinity levels (used exclusively), whereas in Experiment II, brackish water was used only to prepare each of the salinity levels and public water was used (electrical conductivity [ECw] = 0.12 dS m-1) for replacement in all treatments. The increase in the nutrient solution salinity reduced the production of DM and accumulation of nutrients; the reductions were more pronounced when brackish waters were used exclusively (Experiment I). However, the circulation of solutions thrice a day resulted in the harmful effects of the salinity effect. Replacing the evapotranspirated blade with water supply (Experiment II) mitigated the deleterious effects of salinity. Moreover, three circulations of the nutrient solution daily resulted in lower accumulation of inorganic Na+ and Cl- solutes and increased accumulation of nutrients N, P, K+, Ca2+, Mg2+, and S in the culture.
Highlights
Hydroponic cultivation has been rapidly increasing in Brazil, especially for the production of vegetables, such as lettuce (Aquino et al, 2017), arugula (Jardina et al, 2017), watercress (Lira et al, 2019), green onion (Araujo et al, 2016), and tomatoes (Gonçalves et al, 2018)
Plants grown under salt stress exhibit several physiological and metabolic changes, whose magnitude depends on the genotype selected, mineral composition of the nutrient solution, environmental conditions, salinity level, and duration of stress (Gupta; Huang, 2014; Tedeschi et al, 2017)
Hydroponic cultivation using brackish water employs several management strategies, such as circulation frequency of the nutrient solution, which further minimize the damage caused by excess salts and enhance crop production (Silva Júnior et al, 2019)
Summary
Hydroponic cultivation has been rapidly increasing in Brazil, especially for the production of vegetables, such as lettuce (Aquino et al, 2017), arugula (Jardina et al, 2017), watercress (Lira et al, 2019), green onion (Araujo et al, 2016), and tomatoes (Gonçalves et al, 2018). This cultivation system can mitigate the effects of salt stress on plants because the water potential under hydroponic conditions depends on the osmotic potential, and the potential of the matrix is virtually null in the absence of soil (Soares et al, 2016). Silva et al (2016) reported that increased frequency of nutrient solution circulation minimizes the variations in salt concentration and promotes greater oxygenation in the nutrient solution, mitigating the deleterious effects of salinity
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