Phosphorus: Too Much of a Good Thing?

A photograph taken from outer space depicts the 2011 algae bloom in Lake Erie.

Jesse Allen and Robert Simmon/NASA Earth Observatory

There’s nothing like waking up to toxic tap water to get your average citizen concerned about what local farmers are putting in the ground.

For two days last August, 500,000 residents in and around Toledo, Ohio, were told not to drink, cook with, or bathe children in city water. An enormous algae bloom was suffocating the part of Lake Erie where the intake for the municipal water supply is located. The poisonous pea-green soup could be seen from outer space.

Not all algae blooms are hazardous to human health, but the strain that invaded the Toledo shore produces a toxin called microcystin, which, if ingested, can cause ailments ranging from nausea to liver damage. The western end of Lake Erie, adjacent to Toledo, is very shallow and as warm as bathwater in mid-summer. Eighty percent of the surrounding watershed is in intensive agricultural production—much of it devoted to corn, which has very high fertilizer requirements. When rain washes nutrients, especially phosphorus, off the fields, the algae population explodes in the warm, dank brew. “It’s the perfect petri dish,” says Terry McClure, whose family farms 4,000 acres of corn, soybeans, and wheat within the 4-million-acre Maumee River basin, west of Toledo.

Global warming only seems to be making the problem worse. Changing weather patterns in the Midwest have resulted in a dramatic increase in thunderous spring storms: Right when farmers typically lay down a big dose of phosphorus, heavy rains come and flush it from the fields and into the streams. A few months later, those nutrients are aiding the growth of algae rather than corn.

“Technology is going to fix this,” says Terry McClure, citing advances that he and other farmers are already implementing to create a “prescription” for fertilizing their land.

McClure, a fifth-generation Ohio farmer, is one of the early Toledo-area growers to raise his voice about phosphorus in the Maumee basin. A realist as well as an idealist, he doesn’t fit the mold of the average corn and soybean farmer. McClure sits on the boards of the Ohio Soybean Council, Nationwide Insurance Company (a huge corporation with deep roots in agribusiness), and the Ohio branch of the Nature Conservancy. He uses chemical fertilizers and runs a confined animal feeding operation for swine, but also practices a brand of no-till farming endorsed by the most ardent environmentalists, and wants to see his fellow farmers doing more about phosphorus pollution.

“It is unacceptable,” McClure says. “A group of about 30 area farmers have agreed to show what could happen if we experiment with fertilizer on our farms.”

First, though, it’s necessary to find out what, exactly, is coming off those fields. For the past two and a half years, as part of a state-wide program, McClure and the rest of the 30-farmer group have collaborated with Ohio State University researchers to collect daily samples of the water flowing from their farms. McClure keeps a log of his activities for each crop area—such as when and how much fertilizer was applied, and when and with what method the field was plowed—which, along with weather information, is plugged into the project database. The goal is to provide a picture of how the phosphorus leaching from the farm corresponds to the farmer’s choices.

Libby Dayton, the Ohio State soil scientist leading the data collection, says, “The frustration I hear from farmers is that they understand there’s a problem but don’t have the guidance they need in terms of which practices to adopt in order to reduce their [phosphorus] runoff risk.”


As the information continues to pour in and be analyzed, Dayton and her colleagues are using it to update the Ohio Phosphorus Risk Index. The Index, along with the Tri-State Fertility Guidelines (Indiana and Michigan are the other two states), provides directions to farmers on applying fertilizer. A parallel OSU effort, led by Steve Culman, Ph.D., is evaluating and revising the Guidelines. Together, the teams have been developing an online tool that will allow farmers to enter weather information and other metrics on a smartphone and receive an instant, custom-tailored report on how to apply just the right type of phosphorus product in the right amount at the right time in the right way—what agronomists refer to as the “Four Rs” of fertilizer.

“Technology is going to fix this,” says McClure, citing advances that he and other farmers are already implementing to create a “prescription” for fertilizing each acre of their land. McClure’s fertilizer application equipment is guided by GPS software, and some farmers in his area are using drones fitted with infrared sensors that analyze the growth of each crop in order to make even more specific recommendations for the next growing cycle. “You keep overlaying these [methods] to get more accurate,” he adds. “We’re just at the beginning of what we can do.”

While McClure admits there may be a few “bad actors” recklessly spreading phosphorus on their fields, he doesn’t agree with the notion that farmers are over-applying as a general rule. McClure says, if anything, he and most of the farmers he knows apply less phosphorus than what their soil tests indicate. “It’s a very expensive nutrient. A lot of folks are looking for silver bullets…[but] this is about all of us making a slight adjustment. There’s a very small volume of phosphorus coming off every acre, but there are a lot of acres.”

sidebarPhosDon Scavia, Ph.D., an environmental engineer at the University of Michigan in Ann Arbor, has a different take: “Historical overfertilization has left a high concentration of phosphorus in the soil.” Scavia also points out that growing commodity crops on more than 80 percent of any landscape will eventually take its toll. “I think it’s important for people to step back and ask, ‘Why are farmers growing corn?’Farmers don’t wake up in the morning saying, ‘I’m going to grow corn because I like growing corn.’ They’re growing it because the Farm Bill and the market tell them to grow it.”

Noting that some 80 percent of corn grown in the U.S. is converted either to fuel (in the form of ethanol) or flesh (as livestock feed), Scavia is more concerned about the big picture than with what each and every farmer is doing. “There is clearly more that can be done in terms of [fertilizer application] practices that deal better with the dissolved form of phosphorus,” he says. “But maybe we should start asking ourselves, ‘Why are we doing things that drive the price of corn up and make it so profitable?’ Let’s start thinking about the American diet and about changing our energy policy. Can we eat less meat and drive those large market forces in a different direction?”

Phosphorus pollution is not just an agricultural problem, nor is it restricted to northwest Ohio. In parts of the world with poor sanitation standards, algae outbreaks routinely result from untreated sewage. In the Chesapeake Bay and Lake Champlain, both agricultural operations and developed land are in the crosshairs. The “dead zone” at the outlet of the Mississippi River in the Gulf of Mexico can be traced to nutrients flushed from hundreds of millions of acres in America’s breadbasket. When the dead algae sink and decompose, oxygen is sucked from the water, killing off other forms of aquatic life.

During the 1960s, when regulations on industry and municipal wastewater treatment were less stringent, many areas of the Great Lakes suffered from phosphorus pollution and algae outbreaks. But following the formation of the EPA in 1970 and the passing of the Clean Water Act in 1972, a top-down attack on the most egregious polluters has been carried out. Phosphates have been voluntarily and mandatorily reduced or banished altogether from laundry detergent for decades. Ann Arbor, Michigan, which is also in the western Lake Erie watershed, severely restricted lawn fertilizers containing phosphorus in 2006, a precedent that has since been adopted in other Great Lakes cities.

So will farm fertilizer go the way of lawn fertilizer and laundry detergent?

At this point, banning phosphorus fertilizer in agriculture, or even mandating a reduction of its use, is not on the table in Ohio. But last year a new state law was enacted requiring farmers to undergo training in order to apply fertilizer. The course is only three hours long, and farmers have until late 2017 to complete it, but it is one more tiny step toward ensuring that our water is safe.

Brian Barth writes about agriculture, urbanism, and design. He is working on a book titled Invisible City: A Natural History of the Urban Landscape.

Phosphorus: Too Much of a Good Thing?