ASHS 2025 Conference

Soybeans play a crucial role in global agriculture, serving as a primary source of protein and oil, which supports food security, livestock feed, and renewable energy worldwide. The growing demand for food and fuel has intensified the need for soybean production, driving research into soybean cultivation in controlled environments. Manipulating light conditions using specialized LED lights in soybean production is particularly promising, as soybeans are highly responsive to light variations, including changes in the light spectrum. Our objective was to develop compact soybean plants optimized for controlled environments and enhance seed yield by exposing them to various light spectra. Soybean plants (varieties CZ 75 70LL and S16-14801C) were cultivated from seeds in growth chambers (27 °C/26 °C, day/night; 68% relative humidity; 590 µmol mol⁻1 CO₂) in 11 L plastic pots containing peat-moss substrate. One week after germination, the plants were exposed to one of four light spectrum treatments with 700 μmol m−2 s−1 photon flux density. These treatments had different percentages of 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 light), 2) 20B:80R, 3) 50B:50R, and 4) 40B:40R:20FR. Seed yield evaluations showed that the 40B:40R:20FR treatment resulted in a 10% higher 100-seed weight compared with the other treatments for both varieties. The number of seeds per plant increased by 21% in S16-14801C and 11% in CZ 75 70LL under the same treatment. Seed weight per plant was also higher in both varieties under this treatment, with increases of 26% for S16-14801C and 19% for CZ 75 70LL. Morphological evaluations revealed that the shortest plants were in the 50B:50R treatment, with a 2.4-fold reduction in height for S16-14801C and a 1.7-fold reduction for CZ 75 70LL compared to White light. Plants under the 40B:40R:20FR treatment were 33% shorter than those in the white light treatment for both varieties. Additionally, plants exposed to 40B:40R:20FR had 27% fewer branches but exhibited a 19% thicker stem diameter and a 29% higher shoot dry weight than other treatments. These findings confirm that the light spectrum can be adjusted to meet specific goals and enhance soybean cultivation in controlled environments, particularly by increasing seed yield and promoting plant compactness.