Optimizing light spectra for soybean cultivation in controlled environments: Effects on plant growth, flowering, seed production, and seed quality

Abstract Soybeans are essential for global agriculture as a major source of protein and oil, supporting food security, livestock feed, and renewable energy industries worldwide. Manipulating the light spectrum using LEDs presents a unique opportunity to optimize soybean growth in a controlled environment. In this study, we aimed to grow compact soybeans, accelerate flowering, increase seed production, and evaluate physiological variables. Two soybean varieties (CZ 75 70LL and S16‐14801C) were cultivated from seeds in controlled conditions (27°C/26°C, day/night; 68% relative humidity; 590 μmol mol −1 CO 2 ) in 11 L plastic pots containing peat‐moss substrate. A week after germination, the plants were exposed to one of four light‐spectrum treatments at a photon flux density of 700 μmol m −2 s −1 . These treatments had different percent photon flux ratios of blue (B: 400–500 nm), green (G: 500–600 nm), red (R: 600–700 nm), and far‐red (FR: 700–750 nm) wavelengths: (1) 22B:50G:26R:2FR (White; control), (2) 20B:80R, (3) 50B:50R, and (4) 40B:40R:20FR. Both varieties across all treatments reached the harvest stage at 121 ± 4 days, with all flowers being open and producing light‐yellow pollen. Higher levels of blue light in 50B:50R increased leaf transpiration, thereby reducing water‐use efficiency and photosynthetic efficiency. Seed yield assessments indicated that the 40B:40R:20FR treatment increased seed production, rising to 34% in seed number and 37% in seed weight, compared with the white control treatment. Morphological evaluations indicated that plants under 50B:50R and 40B:40R:20FR were 1.7–2.4 and 1.3–1.5‐fold shorter than plants grown under the white treatment. These findings confirm that the light spectrum can be tuned to reach specific objectives and optimize soybean growth and development in controlled environments.