Q & A
Working with manure converts: How to guide them through
How to help producers do their research, refine their goals and tailor expectations
March 28, 2022 by Julienne Isaacs, with files from Bree Rody
This year might see a new crop of converts to manure. With commercial fertilizer prices at record highs going into 2022, incorporating manure into fertilizer regimes might help some producers bring down costs while maximizing soil health benefits.
If you’re an applicator working with producers who are new to the practice, they might have a lot of questions about best practices and how to make sure manure fits into their overall soil fertility plan.
Melissa Wilson, assistant professor and extension specialist in manure nutrient management and Water Quality at the University of Minnesota, shares how you can help new manure users understand the nuances, get the most out of their investment, and stay proactive once you’ve left their field.
MM: What should applicators let producers know about manure in terms of its limitations? What are the best ways to set expectations?
MW: When it comes to comparing manure to fertilizer, one thing to know about manure is that nutrient release is more variable. Manure is the gift that keeps on giving, and nutrients can be released over several years.
But with manure, you get what you get, and it doesn’t always meet the ratios that the crop needs. Crops often need several pounds of nitrogen (N) for every pound of phosphorus (P). However, manure is sometimes more rich in N to P, sometimes by a factor of two to one. Sometimes N and P are equal, but that depends on the manure type.
MM: How does one figure out how much nitrogen the manure accounts for?
MW: So this one is something that varies by region, probably because of different feeding patterns with different livestock, but also because of climate. There will be differences in how quickly the N releases based on where you are.
In general terms you figure out how much ammonia is present, and then you figure out how much N in organic matter is present.
There are calculations for each region that assess how much of the N is plant available.
So there are two parts–ammonium, which is plant available, and organic N, which has to be converted by microbes into ammonium. The calculations help [producers] figure out how much of that will be converted in the first year and how much will be available in the second year, which helps you figure out N credits.
MM: Producers will want to know what to expect in terms of effects on crop and yield. Do you have any real-world examples that can help with tailoring expectations?
MW: We’ve seen some places where the field did not have a manure history, and the crop seemed to have a really nice benefit, and we think that’s maybe due to some of these other nutrients, like sulfur and micronutrients, that [would not be] included in commercial fertilizers if you didn’t pay for them.
In other fields, where there is a manure history, it looks very similar to fertilizer yields, unless the weather is extreme.
In 2020 in Minnesota, the manured fields looked better than where we’d applied fertilizer.
This past year, in the 2021 growing season, we had a drought and crop yields were similar but there was slightly less precipitation.
The organic form of the nitrogen wasn’t able to release as quickly.
MM: Many producers are concerned about excessive runoff and nitrate leaching. How can applicators and producers work together to ease this concern?
MW: That one is complicated, because it has a lot to do with [a producer’s] soil, and if [they’re] doing a lot of tillage and keeping soils loose, with or without manure, [the] soils could blow away or run off. It’s a combination of production practices. Using good practices and applying manure… results could be slightly better than using good practices without manure.
There is some research that’s shown manure can help build water holding capacity and help increase infiltration, and there have been studies looking at the soil microbial activity as well. A lot of that research is really new. It’s interesting to see. Overall, as long as you’re using it judiciously and applying at agronomic rates, it can be beneficial because it’s adding nutrients and helping with soil health as well.
I think some of the bigger issues are that there’s a lot of water that comes with manure and it feels [for producers] like [they’re] transporting water. Manure has a lot of water. As far as what’s more or less economical, the higher the nutrient content per 1000 gallons or tonne is more economical, because you’re carrying less other stuff with it.
MM: Producers are also concerned about soil quality and compaction, and many, particularly in the northeast, dealt with torrential downpours in the past year. How big of an issue is compaction and how can you ensure you’re easing the minds of producers before you bring a spreader out onto the field?
MW: With wet conditions, it can be a big concern. There areadjustments you can make. Make sure your tires are pumped up [at] about 10 to 15 PSI in the field, if you can get them down that low. And they should be higher if you’re on the road, so making those adjustments as you get into the field is really important, [as well as] trying to spread the load out of a wider area. Think about wider width [for tires] and wider axels.
MM: What knowledge should you leave with a new user for after you leave the farm and being proactive between applications?
MW: [Tell them to] nutrient test – so get out in the field, get a couple samples and put them in a big bucket, and then mix that up and create a smaller sample from that mixture and send it into a lab. That’s a really great way to understand what you applied this year, and that can help them manage nutrient management planning for a few years.
Some of the things that might change kind of drastically [if you used] liquid manure is how well it was agitated. Even if you have solid manure. Or if you have hotspots or not, phosphorus [is a factor], because phosphorus can settle to the bottom in liquid environments. The same with nitrogen. If [they] had less nitrogen than expecting, [they] can potentially adjust with the spring application or even side-dress to meet nutrient needs.
MM: Producers also want to know what they should actually be paying for nutrients, and how that compares across different states and manure types. I understand University of Minnesota is working on a national manure nutrient database for the U.S. Can you tell me how that will help increase transparency around pricing and expectations?
MM: When I started my job, everyone talked about book values – “this is how much nitrogen you can expect in swine manure,” “this is how much from poultry.” But all of those numbers are really old – from the early 2000’s… It might have been 20 samples across the Midwest, and that became the book value.
So there’s been a lot of advancements recently. [For example], swine producers are using phytase which helps the animals digest phosphorus a little bette. There’s a lot that changes in our diets, so you have to expect there’s going to be changes in what comes out of the back end too.
So we wanted to update those numbers, and we have all these labs in the U.S. that are analyzing manure across the country. It seemed like a really useful place for us to start to get some of these averages. We think we can have really accurate book values, maybe even for each state.
It’s not [live] yet, but we’re working on the programming. It is so different, the information that everyone collects about the manure. We’re working on it, and will probably be available through University of Minnesota, and in the U.S. we’re working with the NRCS.•
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