2018 ASHS Annual Conference

The use of static or fixed spectral recipes is the predominant strategy for illumination in the indoor crop production industry, regardless of lighting technology used. However, with LED fixtures, it is possible to change the emitted spectrum at different plant growth stages (dynamic spectral recipes) in order to maximize plant biomass and phytochemicals. The objective of this experiment was to compare the effects of fixed and dynamic spectral recipes and end of day far-red (EODFR) light using different percentages of blue (B) and red (R) photon flux (PF) ratios to produce ‘Red Oakleaf’ lettuce. Plants were grown for a total of 47 days with four treatments consisting of two fixed spectral recipes (1) 20B:80R and (2) 20B:80R-EODFR and two dynamic light recipes (3) 20B:80R-EODFR (day 3-19) followed by 100B (day 20-39) (20B:80R-100B), and (4) 20B:80R+EODFR (day 3-19) followed by 100B-EODFR (day 20-39) (20B:80R-100B-EODFR). From day 3-11 plants were provided with 100 µmol·m^-2·s^-1 photosynthetic photon flux (PPF) for 18 h and increased to 200 µmol·m^-2·s^-1 PPF for 18 h from day 12-47. For treatments that included EODFR, far-red light consisted of 6 µmol·m^-2·s^-1 for 30 min. From day 40-47 a “finishing” light recipe (50B:50R) was applied to all treatments to evaluate anthocyanin accumulation in the plant. Plants in all treatments had no significant differences in shoot fresh mass. Plants from the dynamic 20B:80R-100B treatment had 12% greater shoot dry mass than the static treatment of 20B:80R. Dynamic treatment 20B:80R-100B-EODFR plants had 64% longer stem length and 109% greater stem fresh mass, respectively, than plants in 20B:80R. Stem elongation altered the leaf dry mass:stem dry mass ratio resulting in 20B:80R-100B-EODFR having the lowest ratio and 20B:80R having the highest ratio. In terms of canopy diameter, 20B:80R-100B was 26% larger than 20B:80R plants. There were no differences in leaf area and leaf net photosynthetic rate. These results demonstrate that dynamic spectral recipes can be used to significantly impact plant morphology and growth while using similar power consumption.