The Science of Buying Local

Published in Envision Magazine (Purdue College of Agriculture, 2019)
Written by Jessica Mehr

Blue and white tent tops dot the northwest corner of Purdue’s Memorial Mall, shading potted begonias and open cartons of brown eggs. Next to glossy red tomatoes, a handwritten cardboard sign reads “local, picked fresh,” causing staff and students, some with loaves of sourdough bread stuffed in their bags, to stop and inspect them.

The Purdue Farmer’s Market — celebrating its tenth year this May — is one of 8,761 farmer’s markets in the U.S. Department of Agriculture (USDA) database, a testament to the surge in demand for local products over the last 10 to 15 years. Urban farms, community-supported agriculture organizations, and farm to table restaurants — even grocery chains — are marketing local ingredients.

“Consumers want that proximity,” says Ariana Torres, assistant professor in horticulture and landscape architecture and agricultural economics. “The closer you are, the more nutritious it is, the healthier it is, the better quality. That’s why most crops have a price premium for being local.”

Tunnel vision

In response to local food demand, many farmers have diversified what they grow, which has dramatically increased the use of high tunnels. Also known as hoop houses, these dome-like structures are constructed by covering a frame of arched metal ribs with plastic sheeting. From 2005 to 2015, there were over 10,000 new high tunnels constructed in the U.S.,[MSL2] largely due to a funding initiative from the USDA’s Natural Resources Conservation Service.

You can find them on the periphery of Indiana cornfields, packed sky-high with trellised tomatoes. You can find them on large, for-profit urban farms growing peppers for meal kits. Retired hobbyists and young beginners — demographic groups who weren’t farming a decade ago — spend hours pruning while it’s dark each morning to avoid the blistering heat.

By using solar heat and natural cooling, high tunnels extend the growing season, improve crop quality[MSL3] , and increase yield for high-value crops such as tomatoes and cucumbers, which are then sold directly to consumers at a premium price. As a simpler form of controlled environment agriculture, high tunnels are a more reasonable investment for local growers than hydroponic systems or temperature-controlled greenhouses.

However, the hybrid environment of high tunnels poses unique production challenges. “Sometimes a high tunnel has the benefits of growing in the field. Sometimes it has the benefits of a controlled greenhouse. Sometimes it’s worse than both of those environments,” says Laura Ingwell, postdoctoral researcher in the Department of Entomology.

Yet the shift to local production happened so quickly that science is still trying to catch up. There is a shortage of research on high tunnel production, including sustainable ways to control pests, maintain soil health, or compete in the local marketplace.

“These local food systems have value,” says Lori Hoagland, associate professor of horticulture and landscape architecture, “but now scientists are asking, ‘How do we catch up local production practices to be more sustainable?’”

Natural predators

Ingwell and Ian Kaplan, professor of entomology, are performing the first studies on natural ways to control pests in high tunnels.

There was a popular belief that pest levels in high tunnels may be lower than in the field. “We found the opposite,” says Kaplan. Pest populations are higher in high tunnels, as pests enter and establish themselves when the sidewalls are open to prevent crops from overheating. The result: more pesticides are needed, which is problematic in an enclosed space with labor-intensive crops.

“We are really lacking on the science side in terms of what the breakdown of these chemicals is in high tunnels, and what risk they pose for workers and consumer safety,” says Ingwell. In search of a sustainable alternative, Kaplan and Ingwell have found some success with insect exclusion netting, a mesh that keeps larger pests out while still allowing ventilation. They have already passed this strategy on to local farmers fighting cucumber beetles.

They also conducted the first studies [MSL4] on biocontrol in high tunnels, a common strategy in commercial greenhouses. “If you had an aphid outbreak, for example, you would order ladybugs and release them into the tunnel, then hope they stay and kill things,” explains Kaplan.

In a tunnel with open sides, however, predators can migrate away. After unsuccessfully attempting to screen predators inside, Kaplan and Ingwell found that diversifying the environment was more effective. To attract predators, they used herbivore-induced plant volatiles, substances that plants release during pest attacks to attract the pests’ natural insect predators. Pollen and nectar from flowers were then used to maintain the predators in high tunnels.

“The more diverse the landscape is,” says Ingwell, “the harder it is for things like pests and pathogens to navigate.”

Diversity belowground is just as important. “Now we are looking at how the diversity of microbes in soil impact a plant’s resistance to pests aboveground,” says Kaplan.

Microbe nation

That’s where Hoagland’s work comes in. She studies the challenges of local production pertaining to soil health and quality — which is crucial for profits, but also for the health of plants, consumers, and the environment.

“Soil is something that was built up over thousands of years, and within any given soil, there is an entire ecosystem of microbes that are responsible for cycling nutrients and fighting pathogens. Any time you start cultivating soil, you are burning up some of those resources.”

The intense cultivation of high-tunnel soil degrades its quality. Field crops can be rotated, but most high tunnels are fixed, with incentive to plant the same high-value crops repeatedly. Higher production also means that plants need more soil nutrients.

“You can keep putting fertilizers down there as a temporary fix,” says Hoagland, “but the soil will keep sliding in quality.” Using commercial fertilizers and animal manures can cause nitrogen or phosphorous to escape into the atmosphere or leach into degraded soil and contaminate ground water, posing environmental and human-health risks.

Hoagland’s work has shown that degraded soil also makes plants more susceptible to pathogens, which can compromise plant health and cause gastrointestinal illnesses in humans. She is trying to overcome these challenges by learning new ways to manage soil health. In a three-year study of soil in high tunnels, she found that certain green manures (cover crops that are uprooted or tilled under) are effective at increasing microbial activity to maintain soil health. Hoagland is also collaborating with breeders to develop new plant varieties that are better adapted to local production systems.

Trust for sale

“Why would a farmer invest in a high tunnel? Why would a farmer start canning? Why would a farmer grow multiple crops? Every question that I look into,” says Torres, “the answer is the market.” Her research aims to promote economic sustainability for specialty crop growers, which starts with understanding local markets.

When you buy from a local grower, Torres explains, you are buying freshness, quality, and trust. Her research shows that local markets create strong social ties between consumers and farmers. This trust-based relationship allows growers marketing as “local” to access price premiums similar to those commanded by organic crops. By cultivating repeat business, growers can strengthen this economy of trust and promote loyalty.

To help local growers know what a premium price is for their area, Torres is currently collecting foundational data and establishing long-term pricing reports for Indiana’s farmers markets. These benchmarks will help growers develop market strategies for particular seasons and crops.

Options for everyone

Despite dramatic increases, local food production still represents a very small share of the national food supply. Not everyone can afford to pay $4 per pound for local tomatoes, and population growth is creating increased demand for affordable food.

“The local food market trend, in my eyes, created two trends: small, diversified farmers to reach those premium local markets, and big farmers becoming even bigger to fit markets for people who just want a fresh tomato for the best price,” says Torres. “If you sell locally, you will get price premiums; if you sell nationally via wholesale, you make money on volume.”

This diversity in agricultural production gives consumers more control and choice based on their priorities and pocketbook. “Everyone is winning,” Torres says.[MSL5]

The Takeaway

The demand for locally grown produce has surged in the past 10 to 15 years.
High tunnels help meet that demand. These structures use solar heat and natural cooling to extend the growing season, increasing yield for high-value crops sold locally at a premium price.
High tunnels, however, pose new agricultural challenges that scientists are working to overcome.
Ian Kaplan and Laura Ingwell of the Department of Entomology are studying pest control in high-tunnels, including the use of insect exclusion netting and diversifying the high tunnel environment to attract insect predators.
To maintain soil health in the intense cultivation of high tunnels, Associate Professor Lori Hoagland has found that certain green manures help maintain soil microbial activity, keeping pathogens at bay.
Consumers buying local products want freshness and quality, but are also cultivating trust with local producers, says Assistant Professor Ariana Torres, whose research establishes regional pricing benchmarks for specialty crops.
Diversity in agricultural production gives consumers more control over their purchases, based on their priorities and pocketbook.