Field Performance of Transplants Grown using Light-emitting Diodes (LEDs)

Transplants grown using light-emitting diodes (LEDs) were evaluated during subsequent field development to determine if monochromatic spectral light distributions may affect morphology, flower formation or yield. Sunflowers and snap beans were seeded in a greenhouse and allowed to develop under LEDs or natural light supplemented with high-pressure sodium irradiance. The snap beans were grown using LED panels with red (peak emission at 665 nm) supplemented with 20% blue LEDs (peak emission at 455 nm). In addition to red/blue LEDs, sunflowers were also grown under white LEDs (3700 K), or a combination of LEDs (multi-LEDs) using 50% red (660 nm), 10% orange-red (635 nm), 10% orange (600 nm), 10% white (3700 K) and 20% blue (450 nm). Photosynthetic photon flux (PPF, 400 to 700 nm) under the red/blue LEDs used for the snap beans was between 350 to 400 μmol·m^-2s^-1 at plant height. The PPF for the sunflower transplants was approximately 150 to 180 μmol·m^-2s^-1. The day length was 16 h except a short day (8 h) was provided to one set of sunflowers in the greenhouse. Following germination, the seedlings were grown for 7 d under the various light sources. Preliminary results suggest the various types of LEDs support similar growth, morphology and development as natural greenhouse conditions, without significant carry-over effects on field performance. Two selections of sunflowers (‘ProCut Bicolor’, ‘Sunbright Supreme’) were evaluated. Days to flower from transplanting were 50 ± 1.6 d for ‘ProCut Bicolor’ independent of treatment. For ‘Sunbright Supreme’, transplants receiving short days during the propagation stage flowered 8 ± 2.3 d earlier than the 78 ± 1.3 d for the sunflowers under 16 daily h using LEDs or a greenhouse environment. Three French filet type green beans (‘Concador’, ‘Stayton’, ‘Velour’) and the traditional ‘Provider’ were included in the study. The transplants were planted in double rows on 60 cm wide raised beds covered with black plastic. Despite producing the least number of bean pods, the largest yield was recorded for ‘Provider’. The weight of picked beans for one meter length of the raised bed was 8.85 ± 0.78 kg for ‘Provider’ followed by ‘Stayton’ (7.80 ± 0.76 kg), ‘Velour’ (5.42 ± 0.38 kg), and ‘Concador’ (4.18 ± 0.54 kg). Although the yield varied among cultivars, there was no significant difference between snap beans started under greenhouse conditions or the red/blue LEDs.