Editor’s Note: This article is part of Ag & the Bay, a series that tackles tough questions about reducing nutrient pollution from agriculture that reaches the Chesapeake Bay and its rivers.
Pennsylvania’s Chester County is known as the “mushroom capital of the world.” In huge, dark buildings, massive trays stacked several layers high contain compost that is fertile ground for mushrooms.
With temperatures and humidity levels perfected over the decades, mushroom “spawn” burst forth within a few days.
“Mushrooms double in size every 24 hours,” said Meghan Klotzbach, a vice president at C.P. Yeatman & Sons, which has been growing mushrooms for five generations.
They grow in darkness but will soon be bathed in light as crews begin harvesting them. Half of the nation’s mushrooms come from Chester County farms, just outside the Chesapeake Bay watershed.
Much of the compost used to rear the mushrooms is derived from chicken litter produced in Maryland, Pennsylvania and Delaware, trucked out of the Chesapeake watershed to help relieve the nutrient pollution problem in its waterways.
It is a way of dealing with one of the most fundamental problems facing Bay cleanup efforts: what to do with the excess manure produced by the region’s growing population of farm animals.
Areas with large numbers of chickens, dairy cows, beef cattle, hogs or other farm animals generate lots of manure — often containing more nutrients that can be used effectively to fertilize surrounding fields. Those regions send disproportionately large amounts of nutrient-laden runoff to the Bay, where it contributes to algae blooms and oxygen-starved “dead zones.”
Water quality trends in many of those nutrient hotspots have shown little, if any, improvement in recent decades, even as more farmers adopt conservation practices like streamside buffers, cover crops and no-till farming.
Such best management practices, or BMPs, have helped hold the line on nutrients as animal numbers grow and crop planting intensifies. And, in many cases, they have measurably improved stream health and reduced bacteria levels.
But many scientists say they are unlikely to produce the types of nutrient reductions needed to meet Bay cleanup goals.
They suggest that the region should put more effort into tactics that fundamentally rebalance the scales — so that the nutrients coming into a region in the form of animal feed or fertilizer more closely match what goes out in the form of meat, milk or other products.
Such a “mass balance” approach puts greater emphasis on things like trucking manure to other locations or getting farmers to replace chemical fertilizers with regionally generated manure.
“If you’re importing more than you’re exporting, that’s a mass surplus,” said Kurt Stephenson, a Virginia Tech professor of agricultural economics. “And we have mass surpluses in key areas of the [Bay] watershed — the Shenandoah Valley, southern Pennsylvania and the Delmarva Peninsula.”
Stephenson was one of the main authors of a major 2023 report from the Scientific and Technical Advisory Committee (STAC) of the Chesapeake Bay Program, the state-federal partnership leading the Bay cleanup effort. The committee found that efforts aimed at restoring a mass balance of nutrients “offer opportunities for substantial, sustained reductions” in nutrient loads.
The Bay cleanup effort largely hinges on the assumption that blanketing farms with enough BMPs will help meet water quality goals. But many of those, the report cautioned, primarily only delay nutrients from reaching streams or reroute how they get there, such as diverting surface runoff to groundwater. “Most BMPs do not substantially alter mass balances,” the report said.
Several other recent studies have reached similar conclusions. Correcting regional nutrient imbalances, they say, would require a fundamental shift in how excess nutrients are dealt with — and likely require ongoing support from taxpayer dollars.
It’s not a new concept. As far back as 1991, a Bay Program report expressed concern that simply installing BMPs would not meet nutrient reduction goals and suggested using a “mass balance accounting system,” saying that it was “essential to a long-range nutrient management strategy.”
Bay states are moving in that direction. Several are trucking excess poultry manure — the largest source of animal manure in the Chesapeake watershed — to places that need it. And there’s growing interest in technologies that process animal waste to remove nutrients or make them easier to manage.
This year, the region missed its self-imposed deadline to achieve nutrient reduction goals that were aimed at improving Bay water quality. In December, the Executive Council of the Bay Program is poised to reset that goal to 2040. That’s the fourth time it has set a goal and the third time it’s been forced to reset it.
But with agriculture intensifying and animal populations growing, the new goal will be difficult to achieve without new approaches.
“Mass balance is a different way of thinking about the system,” said Zach Easton, a Virginia Tech agricultural engineering professor and an author of the STAC report.
“It’s not thinking about applying specific BMPs to solve whatever a specific problem is.”
A problem with deep roots
The roots of the region’s mass balance problem go back decades. After World War II, huge plants that produced ammonium nitrate for munitions were repurposed to produce fertilizer.
Suddenly, nutrients in the form of nitrogen fertilizers, which historically were in short supply, were both plentiful and cheap.
Agriculture became more regionally specialized as a result. Midwest farmers with deep, rich soil began to specialize in grain production using cheap fertilizer. Farmers in the Mid-Atlantic, close to East Coast markets, began raising more livestock, often fed by low-cost Midwest grain.
It was never economical to ship manure back to the Midwest, where it wasn’t wanted anyway, and the region began accumulating nutrient surpluses. Those were exacerbated as many remaining crop farmers in the Bay region preferred new chemical fertilizer rather than local manure, and their addition to the watershed further exacerbated the regional imbalance.
Increasingly, manure became a disposal problem instead of a resource.
Bay water quality began to decline, too, as nutrients in the form of nitrogen and phosphorus applied to the region’s farmland increased by 90% and 13% respectively between 1950 and 1982.
Livestock numbers continue to increase. In 1985, the watershed had 7.6 billion pounds of farm animals. By 2024, that had increased to 10.9 billion pounds.
Crop production is increasing, too. More is being produced on each acre of land. Corn yields, for instance, have increased at a rate of 1.5 bushels per acre or more in recent decades, meaning more nutrients — often imported fertilizer — get applied per acre.
Despite growing animal numbers and crop production, recent studies show the region’s nutrient surplus on farmlands was decreasing from the mid-1980s until around 2000. But that trend seems to have halted around 2000, those studies found.
“Manuresheds”
Scientists have come up with a word to describe areas with a healthy balance of nutrients: manuresheds.
A manureshed defines the amount of land surrounding an intense animal production area that is needed to absorb manure nutrients in ways that both reduce environmental impacts and maintain farm productivity.
In the days before chemical fertilizers, a manureshed might have only been the size of a farm. Today, manuresheds for intensive animal operations can encompass multiple counties, large watersheds — and even reach beyond.
For instance, a 2022 study looked at applying manureshed management across the entire Susquehanna River basin and found that redistributing excess manure to areas that needed it would reduce phosphorus
losses by about 25%. Nitrogen reductions, though, would be less than 5% — an indication that reaching a balance would require the manureshed to be larger than the river’s 27,000-square-mile basin.
“Whatever scale your mass balance is on — whether it’s the farm, the county, the region or the watershed — if you have more input than your crops are going to remove, you have to have some ways to remove some of that input to start making that math move toward balance,” said Robb Meinen, associate director of Penn State’s Nutrient Management Education Program and a co-author of several recent papers on regional manuresheds.
To rebalance those scales, efforts in the region have encouraged grain farmers to use locally produced manure. That could reduce the need to bring chemical fertilizer into the watershed.
But it’s a complex issue. Manure is harder to manage than chemical fertilizer and often requires different equipment to apply. Unless fertilizer prices are high, there may be little incentive to use it.
“Some people will switch back and forth based on the economics,” Meinen said. “Some people are going to prefer [chemical] fertilizer and get back to it as soon as they can because they own the equipment themselves … they already have money invested in that equipment, and that’s the routine.”
Another complication is that animal manure, especially from chickens and hogs, has a higher phosphorus-to-nitrogen ratio than is needed by crops. If enough manure fertilizer is applied to meet the nitrogen needs of a crop, phosphorus is often over applied and leads to increased runoff.
Poultry manure is dry and can be economically transported further distances. Dairy and hog manures have more liquid and can only be transported short distances.
“At the end of the day, economics drives it all,” Meinen said. “It’s such a big puzzle.”
Tipping the scales
A number of developments may help rebalance the nutrient scale by encouraging more use of manure-based fertilizer.
There is growing interest in promoting healthy farm soils, for instance, and manure is a critical component for that. It contains large amounts of carbon as well as many micronutrients and is a key element to strategies aimed at promoting soil resiliency.
In addition, new equipment allows dairy and hog manure, which are largely liquid, to be injected in the soil. When spread on the surface, those manures release large amounts of nitrogen in the form of ammonia. But when injected, more of the nitrogen is preserved. That helps to better balance phosphorus and nitrogen in the manure, allowing more to be used without over applying phosphorus.
Making the balance sheets add up, though, will require a mix of technologies and incentives. Some of the most significant incentives are state-subsidized manure transport programs.
Maryland started supporting poultry litter transport on the Eastern Shore in 2008.
The program, in which costs are split between the state and poultry industry, has greatly ramped up in recent years as the state has more tightly regulated phosphorus applications on land.
Last year, it supported the transport of 97,409 tons of poultry manure at a cost of about $2 million. Alan Masters, who oversees the program for the Maryland Department of Agriculture, said about 60% goes to mushroom farms in Pennsylvania, 10% to other states and the rest to crop lands in the state which can use it.
Virginia and Delaware also have programs to subsidize the movement of poultry manure. Pennsylvania does not subsidize hauling or track where it goes.
Still, trucking animal manure is a forever task, requiring a steady stream of funding.
But other approaches could help the nutrient balance sheets — and they don’t necessarily mean moving manure. It can mean moving the animals themselves.
In 2022, Pennsylvania provided incentives to Country View Family Farms to build a huge new feed mill in the center of the state, away from the intense animal production areas further south. The feed mill helps hog operations locate in an area with a nearby land base capable of handling the manure.
“If you can put the feed mills in an effective nutrient ‘sink’ basin, then some of the animal industry will follow,” Meinensaid.
Fine tuning animal feed can also have a major impact. Reducing the overfeeding of animals has several results: It reduces the need for grain, the fertilizer needed to grow it and the amount of nutrients in manure.
This has happened to a large degree in the poultry industry, which uses half as much feed per pound of chicken than it did in the years after World War II. And, by adding the enzyme phytase to feed, the amount of phosphorus in excrement has been cut.
Using technologies to treat manure holds promise, too. Some can remove nutrients from manure or change it into forms that are more valuable or transportable.
Several attempts in Maryland to build plants that would use poultry manure to generate electricity failed, as have several attempts to turn animal manure into pelletized fertilizer that could be hauled greater distances and sold.
But those attempts are continuing. In Pennsylvania, a new operation is turning animal manure into fertilizer products that are shipped to New Jersey.
Bay state grant programs are supporting the construction of biodigesters which, while not directly removing nutrients, transform liquid hog and dairy manure into forms that are more easily managed on the land and more economically transported.
They have substantial upfront costs and often require some public financing to build.
Virginia this year announced $19 million for nine projects in a “pay for outcome” program that rewards new approaches and technologies that achieve measurable nutrient reductions.
One of those projects scrubs ammonia, a form of nitrogen, from poultry houses while improving flock health. Another pays participating dairy farmers if they can measurably improve the mass balance of nutrients on their farms.
“Some of the projects that were funded could be nothing, or they could be game changers,” James Martin, director of the Division of Soil and Water Conservation at the Virginia Department of Conservation and Recreation.
He said that type of innovation is critical because, even if the region meets its nutrient goals, it will be continually pressed to maintain those reductions as agriculture continues to intensify to meet growing demand.
But those efforts are not without headwinds. One impediment he and others cite is the computer model that the Bay Program uses to track nutrient reductions achieved by more conventional BMPs. Officials have struggled with figuring out how to credit nutrient reductions for novel technologies, including ones that remove nutrients altogether. For instance, a facility that can process the millions of pounds of poultry manure generated annually at Hillandale Farms in Pennsylvania’s Adams County has sat idle for years.
The process it uses removes ammonia from the chicken manure and produces a product that is more easily moved and applied to the land. But state and Bay Program officials have not been able to agree on how to credit the reductions.
“The Bay Program basically inhibits innovation and investment by the private sector,” said Pat Thompson, president of EnergyWorks. “Even though they keep talking about trying to encourage innovation and make it possible for private sector to invest, it basically blocks it. If you can’t quantify the benefits, you can’t monetize the benefits.”
An uphill struggle
All those approaches — and more — may be needed to reach nutrient goals because the region faces substantial headwinds.
Not only is the human population growing, but the amount of protein we consume is increasing, triggering an even greater demand for animal products. In 2025, more than 60% of consumers report that their intake of protein has increased, according to a survey by Cargill, an agribusiness group. That was up from 48% in 2019.
The trend is likely to continue. Estimates by Penn State scientists in 2020 projected that by 2050 Pennsylvania’s poultry industry could double in size, while beef cattle and hog production would also increase, but by smaller amounts.
It projected that excess manure nitrogen and phosphorus could increase in almost all counties as a result.
Caitlin Grady, director of research and policy at the Global Food Institute of George Washington University, is working to predict the region’s nutrient future. She has been developing large-scale mass balance computer models for the Bay watershed that factor in feed and fertilizer imports as well as export of food and agricultural products.
It paints a dire picture, especially if things do not change. Under a “business as usual” trajectory, with projected agricultural growth and continued BMP implementation, nitrogen loads to the environment could increase more than 20% by 2050.
“We have to think about bigger scale changes to meet the goals,” Grady said. “We can’t assume that we can just do farmer-based practices to meet these goals.”
Meeting nutrient reduction goals solely through reduced fertilizer applications, she said, resulted in reduced food production that would likely be untenable.
Improving the feed formulations for animals was the most effective nutrient reduction strategy, because it both reduced the need for feed and the nutrients in excrement. But because improvements already have been made for chicken feed, Grady cautioned that it was unclear how much more could be achieved.
The bottom line is that Grady’s work shows the Bay watershed does not exist in a vacuum. External market and economic forces will continue to drive production, which drives profits — and nutrient imbalances.
Fixing that will continue to be a challenge and require new approaches. It also poses difficult questions about who pays for that, especially in a food production system designed to keep the cost to consumers low.
“If we’re going to still have animal production in the Chesapeake Bay region and still want this to be a part of our agricultural system, some sort of technologically oriented solution needs to be discussed,” Grady said.
Unless, of course, the demand for mushrooms — and the bedding for them — increases a lot. But even that is not a total solution to the mass balance problem.
The export of poultry manure out of regional nutrient hotspots is counted toward meeting Bay goals — even though, after the mushrooms are harvested, the bedding is removed and composted to produce soil amendments.
Though greatly reduced, those amendments still contain nutrients but are not considered fertilizer. And some of those nutrients — uncounted on any balance sheet — come back into the Bay watershed.
And they still add weight to the mass balance scales.