Sweet Basil Requires an Irradiance of 500 μ mol·m-2·s-1 for Greatest Edible Biomass Production

Energy conservation in controlled-environment agriculture is a major concern for both commercial and research facilities as well as extraterrestrial facilities for food production. Supplying optimal irradiance by using electrical lighting for the greatest edible biomass production potentially is the greatest draw on energy during earth-based or extraterrestrial food production in controlled environments. Our objective was to determine the optimal irradiance for greatest edible biomass production of three cultivars of basil (Basilicum ocimum L.) in a controlled-environment production system. Seedlings of the three cultivars were transplanted into soilless medium, one plant per pot, and grew for 17 days in reach-in growth chambers maintained at 25 ± 4 °C with a 16-h photoperiod. Canopy-level irradiances of 300, 400, 500, and 600 μmol·m-2·s-1 were provided by cool-white fluorescent and incandescent lamps. Shoot growth was measured as height, diameter, and number of leaves 0.5 cm long or greater; and edible biomass was measured as leaf fresh weight, shoot fresh weight, and shoot dry weight. There was no irradiance x cultivar interaction, but main effects of irradiance and cultivar were observed. Plant growth and edible biomass production were least at 300 μmol·m-2·s-1 and greatest at 500 or 600 μmol·m-2·s-1. In several cases, 400 μmol·m-2·s-1 yielded intermediate growth or edible biomass. Within the main effect of cultivar, Italian Large Leaf produced greater edible biomass than 'Genovese', and 'Nufar' yielded an intermediate amount of shoot fresh weight and dry weight. Under our environmental conditions that included ambient CO2 concentration and ambient relative humidity, the rate of growth peaked at 500 μmol·m-2·s-1, and no additional accumulation of edible biomass occurred at 600 μmol·m-2·s-1. Based on our results, canopy-level irradiance of 500 μmol·m-2·s-1 provides maximum edible biomass production of basil in a controlled-environment production system.