Matt Rourke/AP Photo

Potato Farmers Grapple With Climate Change's Impact On Nitrogen Management
While Small Compared To Other Crops, A Wetter State Is Exacerbating Potential For Groundwater Contamination

The light, sandy soil of Wisconsin’s Central Sands region is well-suited for growing potatoes — a root crop that needs an ample supply of water, but is prone to rot and disease. Yet that sandy soil and potato’s high nutrient demand also exposes the region’s groundwater to nitrate contamination. Effects of climate change like increased extreme rainfalls and a longer growing season are expected to make nitrate pollution more difficult to manage. In this series, WPR is exploring how the state can adapt to and mitigate the affect climate change is having on some of Wisconsin’s most iconic foods.

Andy Diercks believes Wisconsin is among the best places in the country to grow potatoes.

Diercks' 2,600-acre farm sits in the Central Sands region of the state, above an abundant supply of groundwater and, as its name implies, a sandy, light soil.

Wisconsin is the United States' third-largest producer of potatoes — an often finicky crop that needs an abundance of water and nutrients and is prone to disease and quality concerns.

But what makes the Central Sands a good place to grow potatoes can also leave the region vulnerable to groundwater quality and quantity issues.

A wetter and warmer Wisconsin has further exacerbated potato farming’s greatest risk to the environment and human health: nitrogen leaking into the groundwater supply.

Farmers and experts alike know the risks of nitrogen contamination — and they also know it's almost impossible to grow an economically competitive potato crop in the region's soil without contributing some level of water pollution.

There are steps farmers can take to reduce these risks, but farmers and experts say consumer demands will also have to change if the goal is to grow potatoes that need less water and nitrogen.

'Growers Hands Are Tied'

Ten years ago, conversations surrounding potatoes and the environment were about water quantity. 2012 was a dry, hot year and potatoes’ need for roughly 20 inches of water during the growing season meant a heavier reliance on irrigation that stressed the region's lakes and rivers.

But today, the conversation’s about water quality.

Nitrogen management is a huge struggle for potato farmers, said Chris Kucharik, chair of the University of Wisconsin-Madison Agronomy Department. 

It's like taking a bath with the plug pulled — water washes through the sandy soil and potatoes' shallow root system into the groundwater table, which can be only 10 feet below the surface in some areas.

Keeping nitrogen in the top couple of feet of soil where the roots are located is incredibly difficult, Kucharik said.


Nitrate concentration from all sources. Graph courtesy of Kevin Masarik, UW-Stevens Point groundwater specialist

"Once it goes below the root zone, it goes to the groundwater system or other surface water bodies, and it's lost," Kucharik said. "There's huge amounts of nitrate leaching in those systems."

State agencies estimate about 10 percent of Wisconsin's private wells don’t meet the drinking water standard of 10 parts per million — in heavy agricultural areas, that can rise to as high as 20 percent of private wells.

While nitrate runoff from all forms of agriculture is also tied to increases in algal blooms in surface water and the dead zone in the Gulf of Mexico, in the Central Sands, the primary concern falls on groundwater contamination.

High levels of nitrates in drinking water are associated with serious health concerns — particularly for infants and pregnant women. Excessive nitrates can affect how blood carries oxygen and have long been linked to blue baby syndrome. Growing research also points to serious health risks for adults.

Potatoes are just one corner of the agriculture industry that contributes to nitrate contamination — the most widespread groundwater pollutant in the state. Statewide, potatoes make up a comparatively small amount of agricultural acreage, but in the Central Sands, they’re prominent. 

Corn isn’t far behind in nitrogen demand, and covers much more acreage than potatoes. Manure, and to a lesser extent septic systems, are also sources.

Just how little nitrate it takes to reach the 10 parts per million water standard often surprises people, said Kevin Masarik, groundwater specialist at UW-Stevens Point. Even with best management practices, it’s often not enough to reach clean groundwater quality.  

John Nichols/WPR

That coupled with a higher frequency of heavy rainfall events, increased precipitation outside of summer and longer growing seasons, and all of a sudden it's getting more difficult to keep the nitrogen in the soil, Kucharik said.

"And the worst place to store nitrogen is in soil," he said.  

"And the worst place to store nitrogen is in soil," said Chris Kucharik, chair of the UW-Madison Agronomy Department.  

Research is also emerging that significant nitrate loss occurs outside of the growing season — which typically runs from April to September — when plants are less likely to be actively taking up excess nitrogen residing there.

On Diercks farm outside of Coloma, he fertigates — applying fertilizer through irrigation — and spreads his nitrogen use out over multiple applications throughout the growing season to lower the impact. But he still keeps an incredibly close eye on the weather.

"That's one of the biggest challenges of farming in this kind of soil," he said. "We have to be real careful not to do that when we know there's going to be a 2-inch rain event coming in two days."

Growers hands are tied, Kucharik said. Without nitrogen, yields would go down. There isn't enough of a natural source of nitrogen in the soil to support the productivity people have grown accustomed to.

"No one could go into that type of soil and get a profitable crop and not end up contributing to water pollution," Kucharik said. "Farmers don't want to drink bad water either, but they are."

"No one could go into that type of soil and get a profitable crop and not end up contributing to water pollution. Farmers don't want to drink bad water either, but they are," said Kucharik.

Yet our memory is too short when it comes to water, said Mallika Nocco, extension specialist in the Department of Land, Air and Water Resources at the University of California, Davis, who spent years studying potatoes and groundwater in the Central Sands.

"When there's a drought, everyone gets really into water," she said. "And when it's wet, we don't think about it. But the thing is, we have to be thinking about it all the time."

Groundwater and surface water in the Central Sands have a notably close relationship because of the shallow groundwater table, located about 10 to 15 feet below the surface in most areas. 

When you see a lake or a stream, you’re seeing the water table, Nocco said. If water levels go down even a little bit, it can affect lake and stream flow.

And as temperatures rise and longer stretches of intense heat become more frequent, farmers will likely need to rely on irrigation more, Kucharik said. Potatoes can’t be water stressed for more than 24 hours.

For Diercks, it can feel like you lose either way. If it rains too much, the crop suffers and risk for groundwater contamination intensifies. If it doesn’t rain enough, pumping water for irrigation can affect surface water. 

"It’s just a matter of how you want to lose sometimes," Diercks said.

An Unpredictable Growing Season

Mother Nature's been difficult the last couple of years, Diercks said, thinking about the sporadic freeze and thaw cycles, intense rains and cooler than usual summer temperatures. 

"If those are climate change impacts, then yeah, we're seeing some changes," he said.

The year 2018 went down as the worst crop in the history of Wisconsin potatoes, said Tamas Houlihan, executive director of the Wisconsin Potato and Vegetable Growers Association.

September rains delayed harvest and before farmers could get into the fields, a devastating early frost in mid-October left some farmers with no choice but to abandon thousands of acres of potatoes in the ground.

"Over 5,000 acres of potatoes were subject to frost and basically useless," Houlihan said. "It was a real disaster."

Potato production contributes about $350 million to Wisconsin’s economy each year. In 2018, roughly 69,000 acres of potatoes were planted across the state. 


Graph courtesy of Dan Vimont, director of the Center for Climatic Research

While experts are cautious to contribute one extreme weather event — or several challenging years — to climate change, the increasing occurrence points to a warming planet. And there’s no historical record to compare it to.

"The saying is, stationarity is dead," Kucharik said. "That's meaning the historical analogs ... are kind of becoming useless because the amount of variability that we're seeing now, there's nothing there in the past."

Warming temperatures are leading to a longer growing season — which in some ways is a good thing for potato production, but it also isn't straightforward. 

When, and how much precipitation falls, what pests can overwinter here and how well cool weather crops will handle rising temperatures are just some of the questions stemming from the 2 to 8 degree change Wisconsin is expected to see by 2050

Future Of The Crop

Gains in agriculture productivity can in large part be traced to the introduction of nitrogen fertilizers following World War II. Today, while nitrogen use has largely leveled out, it still remains near an all-time high.

Alongside those trends have been advances in genetics and breeding, Kucharik said.

Both Kucharik and Houlihan said potatoes that are bred to be more nitrogen and water efficient will likely be used in the future.

But getting consumers and suppliers to accept genetically modified crops is a challenge, Houlihan said. He argues that to produce the quality and yields the market demands, potatoes that need less water and nitrogen and can withstand variable weather, are going to be necessary in the future.

While there’s widespread consensus among scientists that genetically modified plants are safe to eat, they’re controversial, in part because of a lack of long-term research and criticisms that they increase the use of chemical herbicides.

"With words like Frankenfood ... people are afraid," Houlihan said. "But I do think over time we are going to find out that GMO foods for the most part are safe and they're really necessary."

Diercks is blunt that what customers want often doesn’t align with varieties that are easier on the environment and suited for Wisconsin’s climate.

"What we typically end up with here is the Russet burbank, which is what they grow everywhere for French fries," he said. "But it's a 50- or 60-year-old variety that's not particularly well-suited to our humid climate with warm nights."

"There are things that work better here, but they're a little harder to process," he continued.

If companies want their supply chain to be more sustainable, they need to meet growers half-way, Diercks said. 

"If we have varieties that can be more environmentally sustainable, then we need those to be accepted and moved up the food chain," he said. "You can't just continue to ask us to grow and use the same old varieties and just use less water and less nitrogen to grow them — you're going to go out of business doing that."

"If we have varieties that can be more environmentally sustainable, then we need those to be accepted and moved up the food chain. You can't just continue to ask us to grow and use the same old varieties and just use less water and less nitrogen to grow them — you're going to go out of business doing that," said potato farmer Andy Diercks.

Yet an even larger question on the minds of experts is if crop breeding and genetics will be able to keep up with changing environments.

"The question is, will we be able to be growing those particular crops in these regions?" Kucharik said. "Should farmers be looking at alternative potential things they're going to adapt moving forward?"

Wisconsin's potato growers are unique compared to other big potato growing states because of the diversity in potato varieties grown here, said Yi Wang, a UW-Madison professor who focuses on potato and vegetable sustainable production.

Potatoes can only be grown for about three years before they need to be rotated because of disease and weed concerns — farmers typically rotate with canning crops like sweet corn, peas, green beans or row crops like corn and soybeans.

But they are looking for other crops to add to their rotation, Wang said. She’s working with farmers in the region to adopt kidney beans, which need less nitrogen and water and offer a high value. Wang said kidney beans are just one example of ways to diversify.

"We have a growing market both locally and internationally right now," she said. "In Wisconsin, we're not a big producer of kidney beans, but ... it's growing."


Richard Drew/AP Photo

There is strength in running a diverse farm, said Scott Laeser, water program director at Clean Wisconsin, an environmental advocacy nonprofit, and a farmer on a small organic farm in southwestern Wisconsin.

Research shows increasing crop diversity, incorporating more perennial crops and using cover crops mitigate nutrient loss and improve soil health. And in the face of climate change, it can offer farmers more resilience. 

But farmers grow what they grow for a reason, Kucharik said.

"What is that reason? It's your demand, your choices as a part of a society that wants these products," he said.

And it’s important to remember that we're living in a unique period in food production, Laeser said.

"What we've been telling farmers in the marketplace for decades is, 'Grow me cheap food,'" Laeser said. "And so as consumers, we have to recognize that we probably can't have the cheapest food possible and farming practices that are protecting our water and our climate."

Commenting Policy

Wisconsin Public Radio and WPR.org welcome civil, on-topic comments and opinions that advance the discussion from all perspectives of an issue. Comments containing outside links (URLs) will only be posted after they’ve been approved by a moderator. WPR.org will delete comments that violate our guidelines. Visit our social media guidelines for more information about these policies.

Sponsored by:

Sponsored by: