According to the Illinois Soybean Association, Illinois has been the top producing soybean state in four of the last five growing seasons. In 2017, Illinois farmers produced 10.5 million acres of soybeans with an average yield of 58 bushels per acre and a total production of 611.9 million bushels of soybeans. As one of the state’s largest agricultural commodities, soybean crops play an important role in the local, national, and international economy.
Like most plants, soybean crops require sunlight to grow. However, the amount of uninterrupted darkness determines the formation of flowers in most plants. Consequently, the presence of artificial light during nighttime cycles may delay flowering, and eventually maturation, in soybean plants.
In order to quantify the impact of artificial lighting on soybean growth, a research study was conducted in cooperation with the Illinois Center for Transportation; the Illinois Department of Transportation (IDOT); and the
Virginia Tech Transportation Institute.
Dr. Ronald Gibbons, director at the Center for Infrastructure-Based Safety Systems at Virginia Tech, served as principal investigator for this study, R27-172: Roadway Lighting’s Impact on Altering Soybean Growth. “This was a very unique project because we were able to assess the light levels in the fields and then measure the soybean growth and yield by hand harvesting small, 1-meter long sections of plants,” Gibbons said.
In the first part of the project, researchers evaluated light spill from roadways (i.e., light trespass) into soybean fields and then compared those levels of light to the development, growth, and yield of soybeans planted in the
same field, but without light trespass. Several components such as height, reproductive stage, and plant moisture content were measured. The results of these investigations were published in the report “Roadway Lighting’s Impact on Altering Soybean Growth.”
In the second part of the study, captured in “Roadway Lighting’s Impact on Altering Soybean Growth: LED versus HPS Color Spectral Impact,” researchers evaluated whether there was a difference in the soy response to high pressure sodium roadway lighting, versus soy lit by 4,000K correlated color temperature light emitting diode roadway lighting. The light levels were measured in illuminance and converted to photosynthetic photon flux density, which is typically used in the research of plant growth. Both lighting measurements were then compared to the development and yield of the soybeans planted in the field.
“The results showed that high lighting levels would delay soybean development at the end of the season, while low lighting levels did not impact growth. This allowed us to establish a recommended limit of less than 1 lux of light trespass into the field” Gibbons added.
The project was guided by a Technical Review Panel chaired by Mark Seppelt, Electrical and Mechanical Unit Chief at IDOT’s Bureau of Design and Environment. According to Seppelt, “The connection between roadway lighting and soybean maturation had been observed but was not well understood. Our hope at IDOT was to get meaningful data from this research project to modify current roadway lighting design practices and reduce any negative soy impacts.”
“The research established parameters for the magnitude and duration of roadway lighting to promote successful outcomes. Future lighting design practices are being advanced thanks to this and other ongoing research investigating the relationship between artificial light and the environment” Seppelt added.
The research team would like to thank the Illinois Soybean Association, David Holshouser from Virginia Tech Extension, Michael Irwin of IDOT, and site owner Charlie Tomlin for their assistance with this research project. The team would also like to thank the following farmers: Bill Long, Don Ladage, Mike Mouser, Jim Branyan, Joe Heinz, Rich Fullmer, Josh Schlicht, and Allan Klein.