For centuries across the Chesapeake Bay region, farmers have spread manure on their fields to boost crop growth and dispose of animal waste.A tractor fitted with an injector and a pipe to pump liquid manure from the farm’s storage facility injects that manure below the surface in southcentral Pennsylvania. (Penn State Extension)

But stormwater runoff can send those manure-based nutrients into local streams and eventually the Bay. Reducing runoff from farmland is one of the biggest challenges remaining in cleaning up the Bay.

Now, after decades of experimentation and false starts, injecting liquid manure into the ground, rather than on top of it, is gaining traction among mainstream farmers. The method can prevent runoff, make crops grow better and spare neighbors from unpleasant odors.

“It’s ready for prime time, baby!” is the rallying cry of Kristen Hughes Evans, executive director of Sustainable Chesapeake, a group that secured grants to pay for more than 150 farmers in Pennsylvania and Maryland to try manure injection on more than 9,000 acres in 2018.

Her optimism is buttressed by farmer-friendly improvements in injection equipment, more governmental endorsement of the practice and increasing pressure for farmers to control odors as development closes in on their farms. Among the recent changes:

  • The state-federal Chesapeake Bay Program has officially added manure injection as a recognized best management practice, and farmers who use it are eligible to make money by selling nutrient trading credits to offset the impact of pollution in other places. The recognition also means that states can compute the amount of nutrient reductions from manure injection and apply it toward meeting their commitments to the Bay cleanup.
  • In Pennsylvania, the use of manure injectors that only slightly disturb the soil earns farmers state tax credits.
  • A recent four-year study by researchers at Penn State University and the U.S. Department of Agriculture concluded that manure placed in disced slits 4 inches below fields vastly reduced runoff and increased levels of nutrients taken up by plants to help them grow better. That means any added costs of manure injection can be offset by savings on commercial fertilizers that are often spread after crops emerge.

Just as importantly, the study found that a low-disturbance method of injection was compatible with no-till farming and maintaining soil health, long a concern.

The study suggested that large-scale use of manure injection could help Pennsylvania come closer to meeting its nutrient-reduction goals. The state’s progress is lagging badly and suffers, in part, from being underfunded.

Indeed, Pennsylvania regulators with the state Department of Environmental Protection have recently gotten so many comments advocating for manure injection that they are considering adding it to the state’s formal Bay cleanup strategy, known as a watershed implementation plan.

Maryland and Virginia already have done that. Maryland’s WIP calls for 7,226 acres to be treated with manure injection; Virginia wants to have 10,501 acres undergoing manure injection, both by 2025.

Though Pennsylvania does not yet include manure injection in its WIP, its most agriculture-dominated county, Lancaster, calls for 10,000 acres to be treated by 2025 in its own localized plan.

The Lancaster County Conservation District is trying to deploy a demonstration project to introduce the technique to its many Plain Sect farmers. The farmers would have to hire others to do the work because manure injectors are too heavy to be pulled by teams of horses or mules. The idea is to get grant funding so there would be no cost to farmers who participate in the pilot project.

The Penn State study said that governments and conservation groups would have to pony up more cost-sharing money for the practice to make a big dent in Bay states. That is starting to happen. Maryland has a cost-share program for farmers using manure injection. Virginia, in the next fiscal year, will offer cost-share money too.

Another influential study, conducted by Virginia Tech researchers and published in the scientific journal Soil Science, found that manure injection reduced evaporation releases of ammonia (a constituent of soot and a threat to water quality) 87–98%, depending on the soil type. It also cut nitrogen runoff from rain or snowmelt 13–26%.

Why are farmers showing more interest now, after nearly two decades of trying to get manure injection to take root?

Smell is one big answer.

“Increasing development in rural areas and an ability to apply manure that doesn’t cause nuisance calls” is a growing factor, said Mark Dubin, agricultural technical coordinator for the Bay Program.

“We’re working with a lot of farmers that want to do a good job and be progressive. They want the odor to be out of sight, out of mind,” agreed Jeff Zimmerman, owner of Agri-Applicators, a custom manure applicator based in Lebanon County, PA, that spreads manure for farmers.

“They want to be good neighbors. We probably didn’t understand how important that is on some farms,” said Hughes Evans, whose Sustainable Chesapeake group and partners have been busy holding field days to introduce farmers in Pennsylvania and Maryland to the possibilities of manure injection and the costs and benefits of having their fields injected by hired commercial firms or buying equipment to do it themselves.

Technological advances have also helped to move manure injection beyond an intriguing idea toward a workable money-saving choice for farmers.

Early prototypes of machinery that injected manure into fields were clunky, were undersized, couldn’t handle bedrock and rocky soils, and required many refill trips back to manure storage facilities, compacting the soil each time.

Now, a new “drag-line” system comes with up to 2 miles of hose that pumps manure continuously from storage tanks into the injectors mounted on the tractor. That means spreading manure by injection now takes no more time than conventional surface spreading, according to Hughes Evans. New blades inject manure in rocky fields.

“The technology has definitely advanced and made it more feasible in different geographic areas of the [Bay] watershed,” Dubin said.

“I’m a very calculated-risk type of person,” seconded Zimmerman, the commercial applicator. “I’ve been in the hauling business since 2000. I was watching the stuff that didn’t work and now I feel like they’ve finally gotten something that works.”

Convincing farmers that manure injection saves money will likely be the biggest driver for widespread use, experts said.

With more nutrients staying in the shallow ground where crop roots can find them, farmers are finding they no longer need a second shot of commercial fertilizer after crops start growing.

Those on some larger farms already are convinced and are buying their own systems. But most farmers hire companies to apply their manure, and the next leap forward will be to persuade those businesses to invest in manure injectors.

Zimmerman, for one, thinks the demand is on the upswing — enough so that his company has just purchased four manure injectors. And, banking on more large farms wanting to own their own equipment, Agri-Applicators has become a dealership for one brand of injectors.

There are still lingering concerns about manure injection. It doesn’t work well on odd-shaped fields or contoured fields. Prototypes still need perfecting in order to use thicker liquid poultry manure without clogging.

In some areas, there are concerns that injected manure could pollute shallow groundwater, though a Bay Program workgroup found no danger of leaching if recommended application rates are observed.

Studies on how injecting nutrients affects soil health and microbes are conflicting. One found that disturbing microbes in the soil by manure injection caused a slow release of nitrous oxides, a small but potent greenhouse gas.

But backers of manure injection brim with confidence these days.

Said Hughes Evans, “I think we’re beyond the hump of whether this technology is unproven.”