Nutrient and inorganic solute (Na+ and Cl-) content in green onion plants under hydroponic cultivation using brackish water

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.

摘要 采用半咸水开展作物栽培，可使多种植物出现营养与代谢失衡，进而降低植株干物质（dry matter, DM）产量，并使其体内累积有毒离子（Na+和/或Cl-）。本研究针对不同营养液盐度水平结合营养液循环频率，对大葱（品种：Todo Ano Evergreen - Nebuka）的干物质产量、养分及无机溶质（Na+和Cl-）含量展开评估。
本研究采用完全随机设计的6×2析因方案，设置5次重复，在水培系统中开展两组试验：6个营养液盐度梯度（1.5、3.0、4.5、6.0、7.5及9.0 dS·m⁻¹）与2个营养液循环频率（每日2次、每日3次）。试验I中，采用仅用于配制各盐度梯度的半咸水补充蒸散损失水量；试验II中，仅使用半咸水配制各盐度梯度，所有处理均采用市政供水（电导率electrical conductivity of water, ECw=0.12 dS·m⁻¹）补充蒸散损失水量。
营养液盐度升高会降低干物质产量与养分积累量，且当仅使用半咸水补充水量时（试验I），该降低效应更为显著。然而，在试验I的条件下，每日循环3次营养液会加剧盐度带来的有害效应。采用自来水补充蒸散损失水量（试验II）可缓解盐度的有害效应。此外，每日循环营养液3次可降低无机溶质Na+和Cl-的积累量，并提升栽培植株对N、P、K+、Ca2+、Mg2+及S等养分的积累量。