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Possibilities and limitations

Manuresheds offer nutrient redistribution solutions that can provide farmers with economic and environmental benefits, but challenges remain to get manure to croplands that need it and prevent overapplication on fields near livestock.

The term “manureshed” helps to illustrate the amount of cropland that’s needed to utilize the manure nutrients produced in a specific area, or if a given regional area is a nutrient source or sink, explains Curtis Dell, a research soil scientist with the USDA-Agricultural Research Service.

Robb Meinen, an assistant research professor at Penn State, says the manureshed concept allows for defining regional nutrient mass balance challenges and creating solutions.

Under the concept, animals create a nutrient ‘source’ and the cropping area is a nutrient ‘sink’.

“The sink area can be associated with a single farm, and a farm-level nutrient management plan would be a familiar tool that would help many people understand the concept,” says Meinen.

Manuresheds, however, can also be large regional areas where many farms combine to create a large nutrient source.

“This allows us to look at regional nutrient imbalances and explore things that can help to redistribute nutrients from places where they are in excess to places where they can provide agronomic value that is currently not supplied by manure,” says Meinen.

Ray Massey, a retired extension professor at University of Missouri, adds that manuresheds aren’t actually a solution, but a way of visualizing the extent of a problem or an opportunity.

“If a manureshed has excess nutrients, the concept of manureshed does little for current management,” says Massey. “If a manureshed is deficit nutrients, it gives an indication that perhaps a new facility can go into that manureshed and find good demand for manure supplied nutrients.”

Meinen notes manureshed management is widely practiced even if people don’t realize it.

“Manureshed management occurs at the farm scale every time a balanced nutrient management plan is developed and implemented properly by farm management,” says Meinen.

Manure redistribution

Determining the manureshed is a first step to estimating the amount of manure nitrogen (N) and phosphorous (P) that’s produced by a farm, county, or region, and then determining the amount of land needed to safely assimilate that amount of N and P, Dell explains.

“If the specific manureshed has excess N or P, then the people managing that manure will need to evaluate how to get that manure redistributed to fields that need the nutrients,” he says.

Where livestock farms have enough crop acreage to use all the N and P the animals excrete, the manure will likely stay on that farm. It’s only when the farms have an excess of N and P is that farm going to look to find other locations to use the manure, according to Dell.

Redistribution of manure has the potential to offset a lot of purchased P, but less so on purchased N, he notes. Dell points out that soils on livestock farms often already have excess P from a long history of manure application.

“Often those fields have sufficient P for crop growth without added fertilizer or manure, but N fertilizer might still be needed if no manure is applied,” he says.

Massey adds that manure’s concentration – low nutrient to mass ratio – and uncertain nutrient content makes it less desirable than purchased fertilizers.

“The greatest value is gained by livestock producers using their manure on their crops. Selling and transporting manure is more expensive than doing the same with commercial fertilizers,” says Massey.

Redistribution challenges

Actually redistributing manure to where it’s needed is a lot more complex than it sounds, and there are no easy solutions, says Meinen.

For instance, some regions have nutrient sources from several animal species. That’s the case in Pennsylvania, where manureshed associated with swine, poultry, and dairy industries overlap, says Meinen.

“All sources of nutrients should be considered. Manure properties are important as nutrients are easier to transport with solid manures than liquid manures.”

Meinen adds that cropping systems are also a very important component.

“It’s not just about where manure is produced. We need to consider types of crops, crop yields, and crop nutrient demand,” he says.

Meinen also says that getting manure on a higher percentage of cropland is a major challenge with no single solution.

“I view it as a big puzzle where each piece is essential to the final product,” he says. “Pieces of this puzzle could be associated with manure transportation, brokering programs, smart expansion of new livestock farms to nutrient sink areas, promotion of manure treatment technologies. The list goes on and on, but any piece that fits brings us a step closer to puzzle completion.”

Data gap

One of the biggest limitations to implementing manureshed nutrient balances is obtaining complete data, according to Dell.

“For our research articles, we used data from the USDA National Agricultural Statistics Service. However, that data is only available at the county level.”

Consequently, those calculations aren’t as sensitive as they would be if data from individual farms were available, Dell says.

He adds that individual farms would likely have the data on manure N and P production and the nutrient uptake by their crops that is needed to calculate the N and P balance for the individual farm/manureshed. But farmers may lack the time needed to make those calculations, and would need training on doing them correctly.

“However, nutrient management planning does use some approaches to estimate the nutrient balance that are similar to what is done to estimate the balance for a manureshed, just at the level of the individual farm,” Dell adds.

He says that the process of doing the calculations for the manureshed is pretty straight forward, but precision of the analysis could be greater if data was available at a finer scale.

“However, the manureshed may be best suited as a bigger picture concept that is most helpful for informing policy makers,” Dell says. “Other existing nutrient managing planning tools may remain as the preferred approach to determine nutrient balances on individual farms.”

Funding misfocus

A large challenge Meinen sees is that many of conservation professionals are caught up in Best Management Practice (BMP) funding, and are missing some big picture challenges associated with nutrient mass imbalances.

At a conference he attended, he observed that conservation decision-makers were so focused on the distribution of current BMP funding that discussions missed addressing nutrient mass imbalances.

He understands that funding is not only necessary but is a huge part of the puzzle, and that BMP implementation is helping many farms maintain sustainability.

“My point is that we need to keep an eye on the big picture issues – and manureshed exploration allows us to do that.”

Target funding

Meinen has some thoughts about how funding could better directed.

He explains that agencies have developed programming for targeted impaired watersheds, and that this funding prioritizes conservation BMPs in manure source areas.

“Instead, some funding should target watersheds where nutrients are needed,” he says. “Simply, an incentive for a farm to replace fertilizer nutrients with manure nutrients in a region where manure nutrient sources are lacking would help to develop networks of nutrient transport that can exist into the future.”

Meinen says some of the funds directed toward BMP need to shift toward programming that encourages nutrient relocation.

“Something such as a payment per ton of poultry litter taken from a source area to a defined sink area can provide instant removal of nutrients from the source area and are likely to replace some fertilizer application in the sink area,” he says.

Meinen also lauds the usefulness of encouraging smart expansion of animal industries into manure nutrient sink areas, which he says would help to limit the growth of manure nutrients in existing source areas.

“We can’t easily change existing industry structure. There is great opportunity to look at manureshed concepts to find new ways to encourage nutrient redistribution within the system we have.”

Massey points to promising work in aerial photography to locate and identify animal feeding populations.

“The likely opportunity is greatest for large companies that can dedicate someone to aggregate publicly available data and make long-term decisions on where to locate both production and processing plants,” Massey says.

Looking ahead

Meinen reports great work that’s ongoing in the BMP implementation realm in his area, the Chesapeake Bay Watershed: “It is essential work, and I am seeing greater cooperation between producers, agencies, and funders than I have experienced in my career.”

But as he looks ahead, he’s convinced the next frontier in balancing agricultural production and conservation is tackling nutrient mass balance challenges.

“Overcoming nutrient mass balance challenges will take a lot of work, cooperation, and innovation,” Meinen says. “Some pieces to the solution puzzle are yet to be discovered so researchers, agencies, and decision-makers must be open to new ideas and processes.”

He believes solutions must come from two directions – top-down and bottom-up.

“Top-down solutions might involve policy that opens doors for innovation or provides grant funding that encourages targeted programming for nutrient mass balance shifts,” Meinen explains. “Bottom-up solutions start with farm level implementation such as the use of liquid manure injection or solid manure brokering.”