TWIN FALLS — Magic Valley groundwater is getting worse and excessive fertilizer use is to blame, according to the Idaho Conservation League.
The league’s 2020 Magic Valley groundwater report looked at data from the Idaho Department of Environmental Quality, the Idaho Department of Water Resources and other state agencies. That data shows nitrate and phosphorus levels increasing in the Eastern Snake Plain Aquifer, which provides about 300,000 Idahoans — mostly in the Magic Valley — with drinking water.
Nitrogen and phosphorus aren’t inherently bad. They’re critical for plant growth, and there’s some nitrate and phosphorus in groundwater naturally. The problem, Central Idaho Conservation Associate Josh Johnson said, is that farmers are applying more fertilizer than their crops can use. When crops don’t uptake the nitrate and phosphorus in fertilizers, the leftover nutrients seep into the ground and make their way into the aquifer.
Extra nutrients in water might not sound like a big deal. But they can lead to excessive plant growth — toxic algal blooms for instance, which can kill fish and make swimmers sick. High nitrate levels in drinking water could also lead to negative health effects for people who drink that water decade after decade.
The conservation group’s report says manure from dairy cows is responsible for the Magic Valley’s groundwater pollution. Most of the region’s dairy manure ends up being spread on agricultural fields as fertilizer.
“As long as there are 425,000 dairy cows here there’s going to be 50 million pounds of dairy waste a day and we’re going to have to figure out something to do with that,” Johnson said. “It’s not all on the dairy industry, but at least some of it is.”
Lots of manure
In the past few decades the Magic Valley has become one of America’s biggest dairy producing regions. Idaho is now the country’s third-biggest dairy state, and 70% of that dairy comes out of south-central Idaho.
The number of cows here grows every year. In 2019, the Magic Valley had 425,000 dairy cows. Each cow produces an average of 120 pounds of manure a day.
Manure is a great fertilizer. But there are a couple of reasons it might not always be applied to land in the right amounts, Johnson said.
First, manure is heavy and bulky. In most cases, dairymen want to apply their manure to nearby farmland, or sell it to someone who owns farmland nearby. When a dairyman has to ship manure farther, he loses money.
Because of that, there are relatively strong incentives to use manure as locally as possible. There might not be as many incentives to apply that manure in the right amounts. In many instances, applying extra fertilizer doesn’t harm crops much, if at all, even if the crops can’t use it up.
The Idaho State Department of Agriculture inspects all dairies to ensure they don’t use too much manure on their own farms. Idaho Dairymen’s Association CEO Rick Naerebout said the state inspects each dairy an average of five times a year to make sure they’re adhering to an approved nutrient management plan. Those plans prevent dairymen who also farm from over-applying manure, Naerebout said.
“There’s no ag industry more regulated than the dairy industry,” he said.
That level of oversight doesn’t exist for non-dairymen, however. If a dairyman sells his manure to a third-party, the third-party doesn’t have the same application restrictions.
Still, Naerebout said he doesn’t agree with the claim that excessive manure use is the definitive cause of high nitrate and phosphorus levels. In general, one cow produces in a year enough manure for one acre of farmland. Naerebout pointed out there are 2.1 million irrigated acres of ag land in the Eastern Snake Plain Aquifer area.
“Clearly there’s enough acreage there to have a balanced nutrient management system,” he said.
The problem with nitrates
The primary issue with excess phosphorus is harmful algal blooms. Nitrates contribute to algal blooms too, but they can also affect people more directly.
Federal drinking water standards set a 10 milligrams per liter cap on nitrate levels. Above that threshold and infants can get sick with blue baby syndrome —if an infant ingests too much nitrate it can have difficulty transporting oxygen throughout its body.
But that 10 milligram standard was set half half a century ago, specifically for blue baby syndrome, Johnson said. There isn’t a huge amount of good information on how long-term nitrate exposure affects adults, but there have been scientific studies that suggest long-term exposure to nitrate levels higher than 2 milligrams per liter can lead to an elevated risk for colorectal cancer, thyroid disease and neurological birth defects.
In a non-agricultural area, a background nitrate level might be 0.05 milligrams per liter, Johnson said. Most parts of the Magic Valley have nitrate levels in the 2 milligram range or higher.
That’s not crazily high, Johnson said — it’s comparable to other agricultural regions throughout the U.S. But because of the Eastern Snake River Plain Aquifer’s geology, any negative effects of high nitrate levels won’t be felt equally throughout the Magic Valley. It depends on how the groundwater flows.
According to state groundwater data, more than 40% of groundwater well samples in Twin Falls, Cassia and Minidoka counties had nitrate levels higher than 5 milligrams per liter. Gooding (18%), Lincoln (11%) and Jerome (9%) counties had fewer well samples with nitrate levels higher than 5 milligrams per liter.
People who get their water from a city as opposed to a private well have some of that nitrate filtered out, but Johnson said levels that high should still be cause for concern.
Dairy pushes back
Naerebout said the report is frustrating because it failed to recognize the Idaho dairy industry’s efforts to protect the environment.
“We feel like we are doing our part to be good stewards of the land,” he said. “We take water quality very seriously.”
The Idaho Dairymen’s Association has invested $2 million toward the Idaho Center for Agriculture Food and the Environment (CAFE). University of Idaho researchers working at the CAFE will be studying new ways to turn manure into sellable products. In the future, there could be manure processing operations on individual dairies that turn cow waste into different types of fertilizer than can be marketed more widely.
Research at the CAFE could make manure more valuable, which might change how it’s used here.
“To be able to have manure be a revenue stream on the dairy is a vision of the industry,” Naerebout said.
Naerebout also emphasized that the Idaho Dairymen’s Association encourages farmers to plant cover crops and till their fields less often. Cover crops and conservation tillage can help reduce the amount of nitrogen and phosphorus that leach into groundwater.
“It’s honestly a little bit disappointing that ICL didn’t also recognize those efforts by the industry,” Naerebout said.
Virtually everyone agrees that increasing the use of cover crops and conservation tillage would help both farmers and the environment. Both of those practices help fight erosion. The main snags are the up-front cost and education.
“If your family’s been farming a certain way for generations it can seem like a big risk, financially and otherwise, to all of the sudden stop tilling your fields every winter,” Johnson said.
Naerebout said it’s also frustrating that the ICL points a finger at dairy when the cause of the nutrient pollution isn’t clear. Groundwater data shows the presence of elevated nitrate and phosphorus levels, but the data doesn’t reveal the source. Synthetic fertilizers and non-dairy manure could be playing a big role, too, Naerebout said.
“Manure is the original organic fertilizer,” he said. “It’s not this scary, negative thing the report makes it out to be.”
There are a few ways to solve the excessive nutrient problem, Johnson said. The state should keep ramping up groundwater monitoring capacity. On top of that, more farmers need to plant cover crops and practice conservation tillage. Plus, the state should establish a singular regulatory agency to monitor manure use more closely and transparently, tracking the fertilizer even when it leaves a dairyman’s land.