Keywords: plant factory, product quality, light-emitting diode, greenhouse, controlled-environment agriculture, nitrate, photosynthesis, shelf-life.
Light emitting diodes (LEDs) are very efficient and useful sources of light in horticulture. Attributes that have rendered it a favorable light source are their relatively low energy consumption, lower exposure of the plants to radiation heat, long lifetime, flexibility in positioning above or inside a crop, the ability to control the light spectrum and produce high light levels.
Furthermore, control of the light spectrum offered to the plants has been a major reason for applying LED lighting in order to optimize photosynthesis, photomorphogenesis and nutrient content. This brings additional control to the final product quality that was never possible before.
Besides light, plants require the intake of important nutrients such as nitrogen. The preferred source of nitrogen for plants is nitrate. Green leafy vegetables contain relatively high concentrations of nitrate compared to other crops and constitute a significant source of nitrate to the consumer. Because of human health concerns, nitrate content is regulated in Europe. Nitrate levels in vegetables grown in plant factories and greenhouses can be significantly reduced by an appropriate light strategy.
We have shown recently that, offered as a pre-harvest treatment during 3 to 5 days, 100% red light can significantly reduce the nitrate level in lettuce grown in a plant factory. Here we present a more complete optimization on controlling efficiently the nitrate level of leafy greens (lettuce and baby spinach).
We will discuss how to achieve extremely low nitrate levels (< 500 mg/kg) by means of an optimum light sum and spectrum during the growth or pre-harvest treatment in combination with an adapted irrigation strategy (low in nitrate). For both plant factory and greenhouse, this optimization is crucial in order to maintain a high growth efficiency (high g/mol) as well as energy use efficiency.
The original publication is available at www.actahort.org