Lettuce growth and quality optimization in a plant factory

Since the early 2000s, plant factory (or vertical farm) technology has been introduced for growing vegetables and soft fruits. With a well-controlled environment, new health benefits, food safety, optimized nutrients and increased shelf-life can be offered to consumers. With the progress of light emitting diode (LED) lighting efficiency and the knowledge of light-plant interaction, a better quality control can now be achieved together with improved energy efficiency. Growth strategies combining crop quality attributes (e.g., color, nutrients, shelf life) with efficient growth are key for economic viability of plant factories. Most research so far has been addressing quality and growth efficiency separately. Several strategies exist from literature to improve quality attributes, but so far not in terms of optimization of the total growth efficiency including space and energy use. We are aiming to achieve a high growth efficiency (in g mol^-1) and at the same time fulfill the requirements on crop quality; for example: high yield, good color (high anthocyanin index or chlorophyll index) and texture (firmness), high flavonoids content or controlled nitrate levels. An optimization routine has been used with high technical engineering and plant physiology approach in a state of the art plant factory research center at Philips Research Laboratories. LED lighting with a large variety of spectral composition (from UV to far-red) and dynamic control has been used with a total radiation level dimmable per color up to 600 μmol m^-2 s^-1. In this presentation we will illustrate our optimization approach (growth recipe) with specific experimental results on three different red lettuce cultivars with results showing the evolution of the anthocyanin accumulation, spacing optimization and yield during growth.