Map of Mississippi River watershed and Gulf of Mexico

Feed the Farm, Not the Algae

By Jon Gorey, Novembro 1, 2023


Natural ecosystems offer some powerful solutions to our climate crisis. And nature holds answers to other environmental challenges as well—like figuring out how to feed a growing human population without contributing to climate change, pollution, and toxic algal blooms.  

The invention of synthetic fertilizer allowed farmers to double their yields per acre in the past century, supporting some four billion additional humans. But its use and production can have serious ecological impacts. Along with methane from livestock and the carbon released by soil disturbance, fertilizer is a primary reason why agriculture accounts for about 10 percent of greenhouse gas emissions in the US. But new funding models in the Midwest are providing an incentive to farmers to swap status quo techniques for more sustainable practices.    

The high-temperature production of synthetic nitrogen fertilizer is by itself responsible for 1.4 percent of global carbon emissions. After that fertilizer is applied to crops, it can release nitrous oxide, a greenhouse gas 245 times more potent than carbon dioxide. And excess nitrogen also finds its way into waterways, polluting drinking supplies and wildlife habitat and, in the American Midwest and Plains, flowing down the Mississippi River to create a vast, headline-making “dead zone” in the Gulf of Mexico, where it feeds toxic algal blooms that suck the oxygen out of the water. 

“That is the principal cause of these dead zones and toxic algal blooms in the Gulf of Mexico,” says Jim Levitt, director of the International Land Conservation Network at the Lincoln Institute of Land Policy. “The Mississippi River collects fertilizer runoff from Montana all the way to Pittsburgh, and sends it down in one big spout that flows into the Gulf of Mexico, and it becomes this concentrated soup of nitrogen and phosphorus.”  

However, some fairly simple practices can reduce how much fertilizer farmers need, and how much ends up polluting watersheds. First and foremost, says Matthew Helmers, director of the Iowa Nutrient Research Center at Iowa State University, is resisting the tendency to over-fertilize. About a third of farmers apply more nitrogen than necessary, sometimes in an effort to maximize yields or hedge against risk.  

“If we can reduce the rate, and not reduce yields for the crop,” he says, that cuts nitrogen loss as well as costs for the farmer. Iowa State and other universities developed a calculator to help Midwestern farmers determine the best amount of nitrogen to use depending on their goals. And simply fertilizing in the spring instead of in the fall can also reduce nitrogen runoff by an average of 6 percent.  

Beyond better fertilizer management, regenerative farming—a more holistic and sustainable approach to agriculture that can help restore degraded soil, enhance biodiversity, and protect water and other resources—can also help reduce nitrogen runoff. 

One of the most basic regenerative farming practices is planting cover crops in between growing seasons. “That’s where we try to have something green out there during the period when we’re not growing our cash crop,” Helmers says, “covering the soil surface and taking up nutrients that might otherwise be susceptible to loss.”  

A perennial cover crop such as rye or oat stabilizes the soil, but also converts excess water-soluble nitrate into plant matter, “so there’s less nitrate that could be leached away in the next rainfall event,” Helmers explains. Rarely employed just 30 years ago, the use of cover crops nearly doubled in Iowa between 2017 to 2021, to an estimated 2.8 million acres.  

Other in-field practices include a diverse crop rotation—alternating corn or soybean seasons with forage crops, for example—or growing an energy crop such as switchgrass, which can be used to produce renewable natural gas. (That may sound like gas-powered greenwashing, but it’s a real technology.) Low- or no-till farming, meanwhile, which reduces soil disturbance and leaves most of the plant residue on the surface after harvest, can cut nitrous oxide emissions and help soil retain more carbon and nutrients. No-till farming is now employed on 41 percent of Iowa farmland, or 9.5 million acres.


Corn field
No-till farming minimizes soil disturbance, helping soil retain more carbon and nutrtients. Credit: Jason Johnson, USDA Resources Conservation Service.


The edge of a farm offers one more chance to halt nitrogen loss as water drains off the cropland and into nearby waterways. “We have a whole suite of practices to treat that water before we deliver it to a stream, and they’re kind of utilizing Mother Nature to promote denitrification,” Helmers says, referring to the natural process that converts nitrate into dinitrogen, the inert, stable gas that makes up most of Earth’s atmosphere.  

In one configuration, underground drainage systems can be diverted so they release water perpendicular to a stream instead of directly into it, forcing it to flow slowly across a 30-foot vegetated buffer. If the soil in that buffer zone doesn’t contain enough organic matter to promote denitrification, then installing a bioreactor—which sounds high-tech, but is simply a trench full of wood chips—can help do the job. These simple methods can reduce nitrate loss by 42 percent or more

“We could also route that drainage water to a wetland—that might be a riverine wetland next to the stream, or an oxbow wetland, or one that we restore,” Helmers says. In addition to providing ecological benefits to the landscape, “those can be very effective for promoting denitrification.”   

Despite the impact of nitrates on both local drinking water and the Gulf’s marine environment, these practices remain voluntary in Iowa and in most other states. But there are federal and local cost-share programs designed to encourage their adoption, some more robust than others.  

Iowa’s Polk County, for example, offers both financial and logistical assistance for installing edge-of-field buffers, making it easier and more economical for farmers who might otherwise be put off by the hassle or cost. And since water treatment plants are finding that it’s more efficient to pay farmers to reduce fertilizer runoff at the source than to build additional treatment facilities, new funding models have emerged that encourage more farmers to introduce conservation measures to their land.  

The multistate Soil and Water Outcomes Fund, for example, pays farmers to create vegetative buffers, plant cover crops, or employ other regenerative agriculture techniques chosen by the farmer. Later in the year, an independent scientific team measures and verifies the reduction in nitrogen or increase in stored soil carbon. The fund then sells a mix of environmental credits to various public and private entities seeking to meet required or voluntary sustainability goals. Water quality credits, for example, allow water treatment facilities subject to strict nutrient reduction standards to fund pollution mitigation at the source instead of paying for expensive new equipment. Carbon offsets, meanwhile, are tied to the amount of additional carbon stored in the soil.  

Importantly, given the growing and valid criticism aimed at carbon offset schemes, those credits are tied to actual outcomes, “after they have been produced and verified,” says Eric Letsinger, CEO of Quantified Ventures, whose AgOutcomes subsidiary jointly manages the fund with the Iowa Soybean Association. The outcomes-based model is “a demonstrably more cost-effective means of achieving environmental improvements than existing ‘pay for practices’ approaches,” he adds, in a paper prepared for the Environmental Defense Fund.  

“Basically the sewage treatment plant pays into a fund, and the fund will contract with soybean farmers to manage their land in a different way, so as to reduce the amount of phosphorus and nitrogen that reaches the streams,” Levitt explains. “That’s a natural climate solution that is applicable to the entire Mississippi River Valley, and will clean up the water more efficiently than building engineered filters into the streams of Guttenberg, Iowa, or Des Moines.”  

In 2021 and 2022, the Soil and Water Outcomes Fund expanded from Iowa into eight more states, and paid farmers an average of $31 per acre to implement new conservation measures on over 241,000 acres of cropland. Those practices prevented 3.4 million pounds of nitrogen and 206,000 pounds of phosphorus from reaching waterways, and sequestered over 465 million pounds of carbon.  

Still, there’s a lot more ground to cover—literally—including millions of acres in Iowa alone. Cultural barriers remain, with some longtime farmers wary of deviating from a proven formula.  

“We need to get over that hump of changing what’s the norm,” Helmers says, perhaps hinting at the most powerful untapped nature-based solution of all: human nature. “We still need to create a sense of urgency—that we have a problem, and we need to do something about it.” 



Jon Gorey is a staff writer at the Lincoln Institute of Land Policy.

Lead image: This map illustrates how runoff from farms (green areas) and cities (red areas) drains into the Mississippi River, delivering nutrients into the Gulf of Mexico and fueling the annual hypoxic zone. Credit: NOAA.