While “manureshed” may sound like a place to store manure prior to land application, Dr. Robb Meinen, Penn State Extension, described the term as a nutrient management concept.
“A manureshed is the area where there are surplus manure nutrients because of the density of animals,” said Meinen, who spoke recently at a crops conference in Lebanon, PA. “How much land do we need to accommodate and assimilate those nutrients?”
The term is relatively new; Meinen said he became involved with the manureshed concept in 2020.
Manuresheds involve sources (the animal production aspect) and sinks (the cropland available for receiving manure). Manuresheds can be farm-level, county-wide or regional. A mega manureshed is present when there are numerous large-scale farms in one area with excess manure. Poultry and swine manuresheds can overlap.
“A manureshed is the area where nutrients are in surplus in relation to the crops that can assimilate them,” said Meinen. “When there’s an area with surplus nutrients, it makes sense that we would move those nutrients somewhere else if we can. We might move nutrients to a ‘sink’ area in a deficit compared to animal nutrients on site.”
Meinen described the manureshed project as part of a study by USDA-ARS’s Long-Term Agroecosystem Research Network (LTAR). The network spans the U.S. and combines economic, social, productivity, human condition and environmental aspects into goals for agriculture. The original manureshed group included 85 scientists, mostly from ARS.
“There’s a mass balance issue,” said Meinen, noting that the manureshed research began with a focus on swine. “Not just in the Chesapeake Bay area – it’s a problem in a lot of areas. We can’t look just at manure nutrients for swine – there are a lot of other species.”
The initial manureshed work was conducted in swine production areas of Iowa, North Carolina and Pennsylvania. Part of the project involved a simplistic comparison of land application needs based on nitrogen and phosphorus rates in those states as well as the technology required to remove phosphorus from swine manure for transportation from source areas to sink areas.
The study focused on growth in swine and poultry production and considered the typical crop, manure characteristics and application types in each state. Also taken into account was how much land is needed to apply manure on a nitrogen or phosphorus basis.
Meinen explained that swine and poultry operations, which are two of the largest animal industries in the eastern U.S., are quite different when it comes to location, expansion, nutrient transport and odor.
Although swine and poultry are major contributors to available manure nutrients, all species, including beef cattle, contribute to mass balance issues. Photo by Sally Colby
Drivers of operation expansion for both swine and poultry are somewhat similar, but there are some differences. “Keeping nitrogen and phosphorus close to home versus moving it down the road comes into play,” said Meinen. “But there are other influences to think about, including the health and welfare of animals. The swine industry doesn’t want to locate their pigs close to other pigs. They move farther from other pigs, which meant moving north and west in Pennsylvania. That’s a biosecurity and health benefit.”
Swine manure is liquid, heavier and more difficult to transport compared to chicken litter.
“The manureshed impact is that the farms the industry seeks to contract and work with good stewards,” said Meinen. “They need people who can manage nutrients because liquid nutrients cannot travel far. They want someone close to home who can use the nutrients on their own farm or neighborhood.”
The social and animal health impacts of the poultry industry are similar to those of swine, but there’s more concern about traveling distance to the harvest facility.
“They want poultry on trucks for less than 90 minutes so when the animals are off the truck, they can be harvested for quality meat,” said Meinen. “We have the ability to transport litter, which is routinely transported quite a distance through Pennsylvania’s manure broker industry.”
The social aspects of swine production are important considerations. “Swine manure is generally more offensive [to the public] than poultry, so the west and north movement takes the industry to more rural areas with less chance of conflict over odor,” said Meinen. “Animals that are already in the area stay, but new animals are housed north and west.”
Shifting the locations of swine production in Pennsylvania is impacting manuresheds by moving animals, changing their manureshed footprint. The primary swine processor for Pennsylvania and some surrounding states is Hatfield Quality Meats in southeast Pennsylvania. As swine production moved west and north, transportation distance to processing became longer.
Poultry production, even with expansion, has remained in the same area and distance to poultry processing facilities. The poultry industry continues to develop, especially in the face of high fertilizer costs, and can more easily move solid litter to sink areas.
Researchers continue to consider how to relocate nutrients and help producers make changes on the farm. Producers often make operational changes such as riparian buffers and barnyard improvements to improve their BMPs, but there are still many areas that continue to produce more nutrients than can be used locally.
Meinen reported that 26 of the 48 contiguous states have manure hauler certification programs, some mandatory and some voluntary. “Certification has followed the concentration of animals,” he said. “Some areas don’t have the social pressure to force legislation for mandated certification.”
The manureshed challenge is to see what’s new and what’s possible. Scientists in numerous fields related to manure management are coming together to develop and drive policies that will define the future of manure management.
There’s no single solution for correcting mass manure nutrient imbalances. Options include relocating or removing nutrients, or manure treatment technology (MTT) such as composting, anaerobic digestion and solid-liquid separation.
“We expect to see more treatment technologies,” said Meinen. “Hopefully we will see more interest and funding for that.”
by Sally Colby
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