Hydroponics is an increasingly important area of vegetable production. A major and important problem of hydroponics is that some plants can rapidly accumulate high levels of nitrate-N. Greenhouse production is still evolving towards sustainable or environmentally friendly systems. However, the yield and quality of vegetables must be maintained. The reduction of fertilizers must be achieved without compromising market yield. Floating systems for the production of leafy vegetables are increasing, but adequate concentrations of nutrient solution are not yet available. Hydroponic systems are a key tool for indoor plant production, such as artificial lighting plant factories, nutrient film technique (NFT) is commercially used among various hydroponic systems with circulating nutrient solutions. As ion concentrations in nutrient solutions change over time, resulting in nutrient imbalances, nutrient monitoring systems that measure their concentration are required for successful growth. However, such systems are not yet available for commercial use. By regulating the nutrients in the nutrient solution, especially nitrogen, we successfully reduce the amount of nitrate accumulated in leafy vegetables. This can be done by reducing the nitrogen concentration in the nutrient solution a few days before harvesting, or by adding organic compounds, e.g. amino acids. The regulation of some elements, such as suphur, iron, silicon and selenium, has also been shown to be an effective measure to reduce nitrate in the leaves of vegetables grown in the hydroponic system.
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