S08 - Session O4 - Light use efficiency of lettuce grown in vertical farm, greenhouse, and open field

Authors: Wenqing Jin *, David Formiga, Ep Heuvelink, Leo F. M. Marcelis

The energy costs of vegetable production in vertical farms depends to a large extent on the light use efficiency (LUE) of the crop. The LUE is defined here as shoot dry weight per incident photosynthetic photon flux (g·mol -1 ). Quantitative studies on comparing LUE in vertical farming to that in greenhouse or open field cultivation are limited. Values of LUE based on fresh and dry weight of lettuce grown in a vertical farm, greenhouse and open field were collected from literature, as well as relevant aspects like harvest size and cultivation characteristics. The average LUE for lettuce grown in vertical farm was slightly higher than for greenhouse-grown lettuce. Both were substantially higher than for field-grown lettuce. The maximum measured LUE for lettuce grown in a vertical farm is close to the maximum theoretical value. Using the highest reported LUE (based on g fresh weight per mol of light) in a vertical farm can potentially produce annually up to 700 kg of lettuce for each m 2 cultivation area at 500 μmol m -2 s -1 and continuous light. Whether this value can be realised in practice will be discussed. LUE in vertical farms correlated with plant age (or plant size) at transplanting, pH, EC, CO 2 concentration, temperature and relative air humidity. It is concluded that vertical farming has the capability to achieve LUE higher than greenhouse and field production, by optimizing the growth conditions.