Back on April 22 — Earth Day 2024 — a small crowd gathered in UW’s D.C. Smith Greenhouse to celebrate and learn. Attendees sampled vegetarian snacks as they toured each room, the humid air abuzz with energy. The greenhouse is home to an assortment of plants, from cacti to corn, that CALS instructors incorporate into their classes. The facility also hosts a variety of innovative projects and demonstrations, such as a hydroponics system that uses water-based nutrients (rather than soil) to grow cucumbers and tomatoes.

The Earth Day attendees toured the greenhouse and tossed questions at the student scientists who were on hand. The main attractions, however, were the new aquaponics systems.

Aquaponics is the combination of hydroponics and aquaculture, which is the farming of aquatic organisms. In aquaponics systems, fish produce waste that microbes break down into useful fertilizers. In turn, plants use these fertilizers and filter the water to keep it clean for the fish. This symbiotic cycle supports significantly more sustainable water usage than traditional farming methods. Aquaponics also has a more sustainable nitrogen cycle, says Johanna Oosterwyk BS’99, MS’04, who manages D.C. Smith Greenhouse.

“The nitrogen that we use in conventional fertilizers is ‘fixed’ (converted into a form usable by plants) by what’s called the Haber-Bosch process. It requires high temperatures and high pressure, and both of those take a lot of energy,” says Oosterwyk, a teaching, learning, and tech manager in the Department of Plant and Agroecosystem Sciences. But aquaponics instead introduces nitrogen to the system through proteins in fish food, which the fish metabolize and release as nutrients that plants can absorb. “It’s not being transformed from atmospheric nitrogen into nitrate, which is the fertilizer, and that reduces the fossil fuel cost,” Oosterwyk says.

The Earth Day attendees had a chance to explore a system that studies the interaction between aquaponics and low-THC cannabis, also known as hemp. It’s primarily the creation of Dylan Mahant, who graduated in May with a data science degree. Mahant works in the lab of Shelby Ellison BS’06, an assistant professor of plant and agroecosystem sciences who specializes in alternative crops, such as hemp. Mahant’s project focuses on the microbes that convert the nitrogen in fish waste into a fertilizer the plants can use.

“Every plant needs the big three, NPK,” Mahant explains, referring to nitrogen, phosphorus, and potassium. “The big thing with cannabis is that it needs a lot of nitrogen in its vegetative state, but when it switches to flowering, it needs more potassium and phosphorus,” Mahant says.

The hefty nutrient requirements for cannabis make it a good candidate for aquaponics testing.

Mahant’s system uses tilapia fish; however, for future work, he’s interested in seeing aquaponics systems with more species. “Different organisms break down food in different ways, potentially making some nutrients more available to the plants,” Mahant says. For instance, snails eat algae, meaning they can clean the tank and add nutrients to the system. Different crops could also contribute to the system, he says.

Oosterwyk also has expressed interest in adding species to the aquaponics system. “We could use the food that we produce, and any food waste could potentially be fed to insect decomposers,” she says, adding that these insect decomposers could then be fed to the fish, which could help close the loop.

This article was posted in Beyond classroom experiences, Fall 2024, Food Systems, Healthy Ecosystems, Natural Selections and tagged aquaculture, aquapoinics, D.C. Smith Greenhouse, Department of Plant and Agroecosystem Sciences, Earth Day, fertilizer, Hemp, hyrdoponics, Johanna Oosterwyk, nitrogen, Shelby Ellison, sustainability.