Erik Runkle and Qingwu (William) Meng, Michigan State University:

"There is no 'one size fits all' to growing plants indoors"

Vertical farming is hot. Across the world, a violet glow illuminates lettuce and other plants in both large-scale growing facilities and smaller freight container farms. Their owners are often enthusiastic people, but at least equally as important as enthusiasm is the science behind it. To shed some light on this side of the equation, we spoke with Dr. Erik Runkle and Qingwu (William) Meng of the CELL project at Michigan State University.

The Controlled-Environment Lighting Laboratory (CELL) is an indoor vertical farming research facility in the Department of Horticulture at Michigan State University (MSU). "With a goal of benefiting the indoor farming industry, we are exploring ways to increase production and add value to specialty crops by studying environmental and cultural factors", William explains.

As the name suggests, the nexus of CELL projects is lighting, provided by LED fixtures OSRAM developed. Each LED fixture has 7 independently controlled color channels encompassing radiation from UV-A to far red. This precise control enables tests of numerous light combinations on crops grown in multi-layer hydroponic systems.

"We have been investigating the influence of blue, green, red, and far-red light on not only growth and quality of leafy greens, but also flowering of ornamental crops propagated in CELL and finished in greenhouses. Besides research, CELL also attracts students and the general public and informs them of technology-driven indoor farming partly thanks to its location in a heavily trafficked hallway in our building." The impetus to develop CELL came from:
  1. the desire for greater research capacity and
  2. discussions about possibly developing a joint research and commercial indoor farm in Detroit.
"My group started working on indoor plant production in 2010, when I collaborated with OSRAM Opto Semiconductors (based in Michigan) to develop six LED modules for research on ornamental seedlings", Erik tells us. "Those modules have been great research instruments, but after several years of research, we began to be constrained by space and the number of treatments we could deliver at one time."

Another motivating sequence of events began in 2014, when a small group from MSU met with representatives of the city of Detroit, a venture capital and private equity company, a nonprofit organization focused on sustainable water use, and Caleb Harper from the MIT Media Lab to discuss the development of an indoor farm in Detroit. "Although those discussions never materialized into a joint project, Caleb inspired me to develop an indoor facility at MSU—based in part on MIT’s CityFARM—focused on sole-source lighting of horticultural crops", Erik says.

The quest for space and funding
The two biggest obstacles were space and funding, Erik explains. "Space in our building is increasingly limited because of the addition of several new faculty. After evaluating different options, I received permission from departmental chairs to convert what was essentially a storage room into CELL." MSU’s AgBioResearch, which is the college’s research arm, provided funding for the extensive room renovations.

"Meanwhile, I began discussing LED lighting for CELL with OSRAM Innovation based in Massachusetts. Essentially, they asked what I wanted in terms of lighting capabilities and said they would develop it—and they did! The development of these one-of-a-kind modules, as well as the software, took significant effort and resources from OSRAM Innovation to develop, and for that, I’m very appreciative. In retrospect, I was naive about the time it would take, or the cost, to develop CELL. However, I’m extremely excited about CELL, current projects, and future research that we can perform in the facility."

Outreach activities
The CELL team has been communicating the activities in the project in several different ways. In addition to the video below OSRAM created about research missions, they produced videos to showcase the features and experiments in CELL, which are on the CELL webpage. William: "Recently, our CELL story was featured in Futures, a magazine by Michigan State University AgBioResearch. In April, we will be part of the Michigan State University Science Festival and offer tours of CELL to the general public."

The impact of light
The CELL project looks into the effects of lighting on crops. So how does this influence work exactly? William explains: "Plants use light as energy for photosynthesis and as signals to mediate physiological processes such as germination, flowering, and plant architecture. Light quantity, quality, and duration all play key roles in crop vegetative and reproductive growth.

"In CELL, we are focusing on light quality, the colors or wavelengths of light, to regulate photosynthesis, flowering, and production of compounds that influence coloration, nutrition, and taste. Light absorption varies by wavelength in plant pigments and photoreceptors. Certain wavelengths of light can activate or suppress gene expression in regulatory pathways leading to certain crop growth and quality characteristics.

"In lettuce, light quality can steer production of bitter, sweet, and astringent compounds that determine flavor and mouthfeel as well as nutritional value. This is one of the most interesting research areas we are currently pursuing. As for ornamental crops, a low red-to-far-red ratio promotes extension growth and flowering. Yujin Park and Mengzi Zhang, graduate students in our lab, are studying how the interplay of blue, red, and far-red light impacts these traits."

William says that although many crops share similar light responses, considering the diversity of higher plants, responses to light quantity, quality, and duration often depend on specific species and cultivars. "So, it is important to learn about the crops grown and conduct trials to determine proper lighting strategies for desired outcomes."

Practical knowledge
Of course, theory is all well and good, but growers want knowledge they can use in practice. Indoor production of specialty crops is nothing new; plant factories have been in commercial operation in Japan for decades. However, with the rapid advances in the development of LEDs, MSU researchers (and other research groups) are learning how to exploit this technology to produce plants with desired attributes.

"We’ve already written a number of articles about how light wavebands (for example, blue or red) influence plant growth and development, which are available on our floriculture website", Erik points out. "We’ve learned that there is no 'one size fits all' to growing plants indoors, and that several other factors should be considered when selecting a lighting system for crops. For example, the intensity of light and the light spectrum interact with each other, as well as with other environmental parameters such as temperature. In addition, the quality parameters desired for one crop can be completely different for another crop. Therefore, what’s suitable for one crop in one market may not be appropriate for another grower or another crop. Although we’ve learned a lot about plant lighting, many questions remain."

The future of food
And what about greenhouse growers? Will vertical farming ultimately push them out of business? Not according to William. "In my opinion, large-scale greenhouses and vertical farms will coexist and complement each other in future indoor crop production. Greenhouses are often more economical for ornamental crops and high-light fruiting vegetables such as tomatoes, peppers, and cucumbers, whereas energy-intensive vertical farms mostly grow short, fast-growing, and high-value crops such as leafy greens and microgreens.

"Aside from crops grown, the prevalence, distribution, and success of greenhouses and vertical farms will depend on geographical advantages, capitals, energy efficiency, energy availability, energy costs, specific market demand, technological innovations, and government policies. In urban areas, both rooftop greenhouses and vertical farms can provide fresh and local produce all year round. Vertical farms will expand rapidly with improved efficiencies and cheaper, better technologies in the future. The full spectral influence of sole-source lighting on crop appearance, color, flavor, and nutritional value can add value to crops grown in vertical farms."

In certain scenarios, William expects, greenhouses can even incorporate vertical systems for propagation of seedlings and cuttings, creating a hybrid growing method with the best of both worlds.

As for the future of CELL, Erik's team will continue their research on light quantity and quality on leafy greens and ornamental transplants. "Hardware-wise, we would like to automate pH management in the hydroponic system and possibly incorporate CO2 enrichment to further enhance crop productivity. Since the two compartments in CELL are separately controlled, we can probe into how light interacts with temperature, CO2, and nutrient compositions to affect plant growth and development. To support this research, we’re seeking funding from various agencies, including the USDA. We’re open to other crops or research ideas, of course with the prerequisite that we can obtain funding to support such a project."

Dr. Erik Runkle (Professor) and Qingwu (William) Meng (Ph.D. student) work in the Department of Horticulture at Michigan State University.

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