If you’re reading this magazine, you surely already believe that manure is nature’s fertilizer.
But just as chemical fertilizers come in various strengths, ratios and formats, so too do the different types of manure. And, whether you’re managing and applying your own manure, or are an applicator working with producer clients – especially those newer to manure – it’s important to know considerations, benefits and properties of each type of manure and communicate them properly, especially when the choice isn’t obvious. Not all manure is created equal, and each type of manure might mesh differently with the intended soil and crop.
Marcel Sachse, co-owner of Pinsch of Soil Farm in Langley, BC hosts workshops about manure use and planning through LEPS (Langley Environmental Partners Society) in BC.
“It’s a waste product, but in nature it gets recycled to feed new growth,” he says of manure. “You have to be aware of what your crop and soil need in terms of nutrients. You shouldn’t just apply any manure. Chicken manure has a lot more value in nutrients than say horse manure.”
Know the goal, consider the options
Rebecca Larson, professor and extension specialist with the University of Wisconsin’s Nelson Institute for Environmental Studies, would like to see farmers ask more questions before they apply manure.
“I don’t think a lot of people ask why. They don’t really look at their numbers and details and ask why they might want to do something,” she says. “It’s better to understand where you’re trying to improve or what you’re trying to do.”
The objectives for the manure’s application need to be determined prior to choosing and spreading it. Is the goal to reduce input costs, like that of fertilizers? To improve soil health, including adding organic matter? To increase certain nutrients in the soil? Is potassium high, but nitrogen low? Can changes to the manure result in cost savings? Increase yield?
With specific goals in mind, farmers may learn that the manure at hand may not be the right fit. But there may be an option to manipulate it to improve its suitability. Or, manipulation may make it possible to transfer manure to other farms and trade for, or purchase another, type of manure that’s a better fit.
Separating dairy manure, for example, may result in more organic matter in the solids and higher available nutrient concentrations in the liquid which become two separate products. Swine and other manures can also be separated, and Larson says this allows for more opportunities in usage.
“Each system is really variable,” she says. “If I look at all these systems, I need to know if it’s worth the cost to process. The circumstances of how it’s going to be used is a big part of determining the equipment. And any processing may alter the manure, changing what you want to do with it.”
For many farmers this presents a challenge. Dairy farmers are used to spreading their fields with dairy manure, but what if that’s not what forage fields need? The soil may have indicated compatibility in the past, but perhaps that’s no longer the case.
Management based on properties
How any type of manure is managed depends upon the form and nutrient values of the manure. For example, poultry manure or litter, with its typically dry consistency and high NPK concentrations, needs to be managed in a way that reduces nitrogen losses when it is applied to the soil. It can’t be easily injected like a liquid manure.
“You need to pay attention to some very different things once it’s applied, than if you’re applying something like dairy manure,” say Larson, of poultry manure. “Dairy manure is more liquid, compared to poultry, changing the entire manure management system from collection to land application because your manure is different.”
Liquids usually make sense to move only up to within a few miles due to the high costs of transportation, says Nancy Bohl Bormann, a manure and nutrient management researcher with the University of Minnesota.
“Some of the manure, on the other hand, is more concentrated. Especially some of the solid poultry manure. It can get trucked further because of that,” she says. “If you could use all the nutrients on a field, you can justify hauling it further. There’s the cost benefit.”
As a rule, poultry manure is the queen bee of nutrients and most often is a dry manure. At the other end of the nutrient scale is solid dairy manure, which has the lowest average range of nutrients among other livestock manure ranges provided by ManureDB data from the University of Minnesota.
Beef is interestingly higher in nutrients than dairy in its solid form, but lower in liquid/slurry form. Liquid swine manure has the largest range of nutrients, likely due to differences in manure storage from open lagoons to deep pits and is similar to liquid/slurry dairy manure and falls at a higher level than horse or dairy solids, but still significantly lower than poultry.
Smaller scale farmers with chickens and/or sheep may find that their farms produce substantial nutrient benefits that could be used on farm or sold. But standard practices apply says Sachse.
“Manure should be composted usually at least three months,” he says. “When it’s been composting for at least three months, you can call it a soil amendment, your nutrients are more stable and less volatile.”
He adds that fresh manure should never be applied to food that will be harvested within four months.
Test and find the right fit
Manure calculators, such as the one through Manure DB, are helpful to create an idea of general nutrient values. There are some crops that are a natural fit for the nutrients in certain types of manure.
“Liquid swine finisher manure is a great match for corn production,” says Bohl Bormann. “The nutrients are well balanced for corn. The nitrogen is more readily available compared to other manures.”
And while generally, this is a match made in manure heaven, there are still factors to be considered according to Teng Lim, an extension professor of the Plant Science and Technology Division with the University of Missouri. He recommends testing the manure being considered – every batch if possible. Testing itself requires care and attention, especially with manures in deep pits or lagoons like swine or dairy manure.
“That manure could have been sitting there for months,” he explains.
Using a sludge sampler that takes a core sample from the crust through the pit to the bottom is recommended before the pit has been agitated. Testing is best done after good agitation during pumping out. Larson’s research recommends composting many manure samples during the emptying process, taking some from every few tanker loads, then mixing the samples together and sending a sample in for analysis.
“Even with that, you can still see some differences,” Lim says. “Though commercial scale farms, they tend to be a little more consistent in how they manage the farms and what they feed the animals.”
Data from the manure will inform the applicator of flow rate and speed and hiring a custom applicator team will bring the necessary expertise to balance field needs with nutrient availability. Plus, a manure-spreading team will have the tools to do the job more efficiently.
“It’s quite exciting to be thinking about what we have now versus 20 years ago,” he says. “We are constantly improving and the more professional these teams are, the better.”
Shape and form matter
More solid manures, like poultry or beef are going to have a slower release of nitrogen, so while the numbers for soil need and manure nutrients may line up, there is a time factor as to when that nitrogen becomes available, says Bohl Bormann. Liquid manures are generally incorporated into the soil, so nitrogen stays where it’s needed, un-managed solids have more of a risk of losing their precious nitrogen through volatization (off-gassing) because they are exposed.
“That’s another tricky thing about manure. In solid manures [nitrogen is] not necessarily going to be released right away either,” she says. “Planting a cover crop after a manure application can help reduce nitrogen loss.”
The four Rs
The USDA and other agricultural organizations promote the longstanding “four R” tradition for applied nutrients: right source, right rate, right time and right place.
While the principle is often used to refer to commercial fertilizers, it has value in the application of manure, and Lim advises following the guidance for manure as well – regardless of manure type.
“Those are the basic principles whether it’s pig manure or poultry manure,” he says. “Manure can be very different from farm to farm or region to region or even with timing. That’s why the four R principles are always important.”
Keep it in balance
Crop fields usually benefit from manure application, but in many cases the source of those benefits exists outside the land’s normal ecosystem. The desire for additional nutrients needs to be balanced with environmental impacts.
“Wildlife is in a closed ecosystem,” Sachse says. “Their nutrition is usually from the same habitat which they fertilize with their own scat. Our dogs and livestock on the other hand are fed something that comes from outside of that ecosystem. You basically import nutrients and now we do have to think about where we apply that manure. If you don’t know what your soil needs, you quickly over-apply, excess nutrients leach into watercourses and bring things out of balance.”
Grass-fed cows may be considered to be eating from within the ecosystem where their manure is applied, but swine that have food trucked in would not. Therefore, application decisions begin with soil needs, says Bohl Bormann.
“A basic tenant of nutrient management is soil testing,” she says. “Do regular soil testing to know what you even need to begin with.”
Soil testing is the first step to understanding the nutrient support required for the future crop. This should be followed by testing the potential manure to gauge for application rates and overall compatibility. While general assumptions can be made about which manure type is best, even within the same species, manure can be dramatically different; such as manure from a dairy farm with a primarily grass diet compared to one with a blended diet. Manure storage type and climate can also greatly impact manure.
“Fertilizer prices are very expensive, so it makes manure worth more than it had been,” says Bohl Bormann. “You need to know your soil and your manure by the numbers. The carbon and microorganism additions can be added soil health benefits as well.” •
