Closed loop grows crops, fish
By LACEY JARRELL
OREGON CITY, Ore. — Hot sun radiated through the shade cloth atop Nick Fox’s 85-foot-long greenhouse as he walked down a narrow gravel path next to two indoor water bays.
Evaporated water moistened the air, mixing with sweat droplets forming on Fox’s forehead as he explained his plans to fill two of the bays and expand Grass Roots Aquaponic Farms into a full-time community supported agriculture program.
Next to one of the four 1,800-gallon bays, Fox stopped and leaned over. In front of him, rows of lettuce spaced six inches apart grew from foam pads floating on the water.
Wiggling a head of lettuce loose, Fox gently tugged it upward. Its long white roots, glistening with water, trailed behind — not one speck of soil is visible.
The method Fox used to grow this lettuce — aquaponics — is a mixture of hydroponically growing plants in nutrient-rich water and aquaculture, or fish farming.
Fox explained that instead of dirt, the plants’ roots float in water, absorbing nutrients that pass through a looped system that begins with a 900-gallon open-air container filled with tilapia, a species of freshwater fish grown for food.
A closed loop
Except for fish food and light, an aquaponic system is a closed loop. It uses up to 97 percent less water than a traditional garden because once water enters the system, it is continuously recycled.
“It’s like you’re taking a perfect mountain stream system and synthesizing it for your own purpose,” Fox said.
Aquaponic growers can use trout, perch, bass or catfish as the foundation of their systems, but the most popular fish is tilapia, said David Haase, owner of Greenhill Gardens fish farm in Eugene, Ore.
“What makes tilapia ideal is they have a flesh texture similar to halibut,” Haase said, adding that tilapia filets can fetch as much as $12 per pound.
More importantly, Haase pointed out, is that for every 1 pound of fish produced, 10 pounds of vegetables can be grown.
Leftover greenhouse vegetables can also be fed to the fish, Fox said, pointing at decaying red apples and leafy greens floating in the water. The healthier the fish are, the better the plants will grow. Most lettuce is ready for harvest in about four weeks.
The water passes through a three-step filtration process before it reaches Fox’s vegetables.
“If you have solid material in the tank it will bond with the roots, and your plants will die. They really need the nutrients to be soluble,” Fox said. “Dirty water is kind of a misconception. The clean water still has all the nutrients. You’re after the ammonia, which is excreted from the fishes’ gills.”
First, Fox explained, movement from tilapia swimming in the holding container loosens suspended particles and heavy materials. The sediments rise to the top, where they are drawn into a gravity-fed filtration tank.
Standing outside the greenhouse, Fox opened a ground-level valve and green sludge spewed out. In this second step, he said, baffles separate the solid material before it settles at the bottom, where it can be collected and used as outdoor garden fertilizer. Clean water drifts upward, before being suctioned into the final filtration step.
“The third tank has about six or seven filter media, so it basically polishes the water before it is pumped into the plant beds,” Fox said.
Water that has been filtered is pumped back into the greenhouse, where it streams underneath the foam pads floating in the water bays and saturates the suspended plants’ roots with nutrients.
Clean water flows back to the tilapia tank, where the process begins again.
The greenhouse, Fox explained, was purchased used and most of the construction materials were gathered through other second-hand outlets. When repurposed material couldn’t be found, Fox kept costs down by substituting inexpensive parts, such as toilet flanges, for high-dollar mechanical and structural materials.
“This is a small scale example to see how cheap we could build it and how sustainable it could be,” he said.
Each of Fox’s four bays is large enough to produce 1,000 heads of salad greens. The long rectangles take up nearly the entirety of his 2,500-square-foot greenhouse — save for one strip where tomatoes, squash and cucumbers grow.
“In a really well-maintained aquaponic system, you can grow double or triple what you can grow in an average system,” said Nate Storey, co-founder of Bright Agrotech in Laramie, Wyo.
But not every crop can be grown that way. “The general rule of thumb is: If it’s harvested by combine, it’s probably not going to be efficient to grow,” Storey said.
Storey’s aquaponic system sustains a year-round supply of garden greens and herbs and 500 pounds of tilapia in two 2,000-foot greenhouses. Rather than stretching his garden outward, Storey grows it upward in specialized tubes that allow more than four more times the yield per square foot than traditional row planting.
It also allows Storey to reduce overhead costs by taking whole plants to market and letting consumers hand-harvest produce themselves, he said.
“Sixty percent of the cost is post harvest in labor and packaging,” Storey said.
Crops such as potatoes, beets and onions can also be grown using aquaponics, though not submerged in water. Subterranean species and trees that are suitable for greenhouse environments can be cultivated by circulating the nutrient water through a potting medium like gravel or clay pebbles.
“Everything can still be grown organically,” Fox said.
Aquaponic options for pest control and fertilizers are inherently limited because fish are extremely sensitive to chemicals. Organic certification from the USDA is rare, but growers like Storey and Fox said because the system is closed — except for the fish food — as long as the fish are eating organic, everything after that step will be organic.
Olivia Hittner and Michael Hasey, owners of The Farming Fish in Rogue Valley, Ore., gained their organic certification two years ago.
Hittner said although their aquaponics system does not use soil, the process is similar to traditional garden certification: “(The USDA) reviews the system plan that outlines the aquaponic processes to confirm that only organic inputs are being used.”
In many states, fish breeders and aquaponic gardeners must purchase licenses to transport tilapia or other fish to new facilities or to sell them to a third party.
In Oregon, residents growing tilapia for personal use are required to pay a one-time $12 transport fee. State law prohibits raising tilapia in outdoor ponds or tanks where they can be caught by animals or washed into freshwater streams by flood-level waters, which means an Oregon Department of Fish and Wildlife biologist must visit the purchaser’s site for a biosecurity inspection before fish can be moved.
“We don’t want to take any chances with the tilapia getting into the environment because it is an exotic species,” said Guy Chilton, ODFW biologist.
Commercial distributors must pay a recurring $127 annual licensing fee and fall under the same inspection regulations.
Fox doesn’t plan to sell tilapia commercially just yet, he said, lifting a one-gallon container full of tilapia fry from the tank’s cloudy, green water. The fish are the anchor point for the entire aquaponics system, but the aquatic environment is also the most difficult aspect of the process to perfect.
“My suggestion is to start small and start playing around,” Fox said. “This system can take six months or a year or more to mature.”