Manure Manager

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Injecting for success

Liquid manure isn’t perfect for every operation.

November 21, 2023  by Jeff Tribe

Liquid manure injected directly into the soil, versus surface or broadcast application, can cut down on nutrient losses through preventing surface runoff and volatilization. All images courtesy of Melissa Wilson.

Chill out.

Realize opposites attract.

It’s OK to be needy.

And don’t forget to close the loop.


The above might be appropriate for delving into online dating. But they’re also pivotal reminders for farmers maximizing the positive impact of liquid manure application through injection.

The largest differentiator in liquid manure application is surface versus injection. The latter can be particularly advantageous for no-till systems, cutting down on nutrient losses through preventing surface runoff and volatilization, loss of applied nitrogen as ammonia gas.

That might prompt one to ask: “If it’s so beneficial and simple, why isn’t everyone doing it?” To answer that question, it comes down to one fact: it might be beneficial, but it’s not necessarily
“so simple.”

Curtis Dell, research soil scientist, USDA-ARS-PSWMRU, cites expense, time and tractor horsepower required over surface application.

“That’s probably the main barrier to getting it out on more farms.”

Growing up in Indiana, Dell’s educational background includes a degree in agronomy, a masters in soil microbiology and PhD in soil microbiology with an emphasis on nitrogen cycling. His work history includes carbon sequestering in soils, carbon and nitrogen cycling and manure management, including nitrous oxide and ammonia emissions. Dell’s career reflects a cross-section of environmental considerations with maintaining agricultural production, but (in his words) “helping farmers do it in a way that’s the most sustainable and least impactful.”

Liquid manure injection might be viewed as a positive, one-pass, multi-tasking option. There are, however, associated concerns around the potential for creating an environment conducive for denitrification, a microbial process ultimately resulting in nitrous oxide gas.

“That’s a continuing area for research with injection,” says Dell.

Chill out
Injection while cooler – a.k.a. “chilling out” – and at times when plant nitrogen uptake is maximized are seen as countermeasures for controlling production of unwanted gasses.

“The timing of manure with crop uptake, crop demand, is probably one of the better ways to cut down on nitrous oxide as much as possible.”

Dell says injection is most common in no-till applications, and holds the advantages of getting manure off the surface without “a whole lot of disruption” maximized.

There are many application technologies, each essentially opening up a slot for manure to be injected into and ideally closing that loop afterwards. Most of Dell’s work has been with shallow disc injection, most commonly used with row crops.

Manure injection began with chisel-based systems in Europe before catching on here, he notes.

“It did more disturbance than you’d probably want in a no-till system. If you are doing no-till, you want as little disruption as possible, the shallow-disc seems to be the best for that, even
with tillage.”

His work began mainly with straight discs but has evolved to ‘wavy’ models. “It’s still fairly diminished disruption.”

Liquid manure is most often injected into corn ground, says Dell. “That’s where we’re putting down most of our nitrogen and nitrogen conservation is most important.”

Soybeans are generally not a target unless storage capacity is a consideration. Injection can be used in pastures, although need is considered less because perennial cover and grass roots create lower runoff than barer ground. Injectors cut some roots or crowns, but a New York study found yield was not seriously affected.

“You’ve got some nutrients there [that] they’ll take advantage of.”

There’s also a growing trend to inject liquid manure into live cover crops early in the season, which are then cut as forage. Although done for other reasons, this also cuts down on ammonia volatilization but with less potential for nitrous oxide emission compared to injecting manure after the cover crop has been killed.

Soil type is not a huge factor, although rocky Pennsylvania fields in Dell’s area can minimally disrupt application.

“It’s not perfect because you have patches of manure up on the surface, but you tend to get most of the manure in
the ground.”

He’s seen studies indicating some nitrate leaching may be related to injection in very sandy soils with shallow tile drainage. There appears to be less concern in loamy fields.

“Although that’s not an easy thing to measure.”

Field technicians who measure odor levels with devices ultimately sourcing their noses and farm neighbours may also appreciate liquid manure injection’s tendency to limit fragrance.

“It wasn’t the original intent, but it’s a good side benefit,” says Dell, who sees liquid manure injection as an overall positive.

“And in no-till systems it can get around the issue of higher ammonia losses if you’ve leaving the manure on
the surface.

Melissa Wilson, associate professor and extension specialist in manure nutrient management and water quality with the University of Minnesota, has also done more than scratch the surface on liquid manure injection.

And while she too is a fan, Wilson warns “There is never a silver bullet, there is always trade-offs.”

Liquid manure injection offers more but also takes more effort than heading into a field, opening a valve on a tank and driving up and down.

“You’ve got to have the equipment and set it up right.”

Even distribution to avoid streaking, optimal depth, proper calibration and ensuring no nozzles are plugged are included in required preparations.

“All of these settings, you have to tweak.”

Whether going deeper using shanks, with or without sweeps, or shallower with discs or double discs, the key to injection is opening the soil, creating a pocket and closing it up. Wilson recommends taking soil’s loading capacity into account along with dilution rate of the liquid manure – dairy tending to have more water in its composition, for example – into consideration. Individual calculations recognizing specific variables ensure the injection pocket is properly filled, not over-filled, thereby defeating the purpose.

Liquid manure injection can be especially advantageous for no-till systems.

Opposites attract
Wilson believes any soil type benefits from nitrogen conservation. Adding manure’s organic matter also increases a soil’s water and nutrient holding capacity, providing negatively charged ions for positively charged ammonia ions to bond with – opposite charges attracting. This keeps the nitrogen attached to the soil instead of converting to a gaseous form.

Ammonia readily converts to ammonia gas, adds Wilson. 

“Once it’s in the air, it’s not fertilizing your crop.”

It can drop out anywhere, she continues, and also be a precursor to particulate matter, a particularly nasty and unhealthy form of air pollution.

“I’m sure anyone who’s had a strong whiff of ammonia knows what I’m referring to.” The smell can be equally sour on farmers’ bottom lines, given the cost of commercial fertilizers – which has been a particular pain point for the last several years.

“Injecting and incorporating is how you preserve nitrogen,” says Wilson, referring to experimentation around injecting between rows of corn plants, “almost like side dressing.”

“We’ve been seeing really nice results with injecting it during the growing season.”

Wilson says data suggests corn plants at the V5 and V6 growing stages or beyond are susceptible to damage from draglines, but growth isn’t affected up to the fourth leaf collar.

“You can drag a line over it and it will come right back.”

Considerations within that include the respective composition of liquid dairy (50 percent ammonium, 50 percent organic nitrogen) and hog (75 percent ammonium, 25 percent nitrogen) manure. Dairy manure’s organic nitrogen takes longer to release during the growing season, rendering it less attractive in some years.

Beyond potential commercial fertilizer savings, Wilson cited one hog operation which in going from two to 2.5 turns per year, with larger animals, found they couldn’t get through a year with existing manure storage.

“With this in-season application, they can apply to one field and hold off to the fall.”

Climate also has a significant impact on liquid manure injection.

Experimentation continues around shallow, low-disturbance injection technology, but it’s most often done without crops in the ground. Planting, growth and freeze/thaw cycles do affect timing. Most injection in Maryland happens in the spring, compared to a majority of Minnesota’s in the fall, a still significant portion in the spring and the balance in between.

Related to timing, in the same manner of putting food into a refrigerator to slow microbial degradation, taking temperature into account can limit the microbial process leading to nitrification, or the process of ammonium converting to nitrate.

“We recommend waiting for soil temperatures to be 50 degrees (Fahrenheit, equivalent to 10 degrees Celsius) or lower,” says Wilson.

In conclusion, while not right for every situation, liquid manure injection in the fall, spring or possibly even summer may be the right thing environmentally as well as helping provide the best bang for farmers’ manure ‘buck.’

“It’s something to consider,” concludes Wilson. •


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