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Solid results from liquid manure

If you’re in the business of selling or applying liquid manure, it’s likely been a busy few months – and it could get even busier.

One of the many cascading effects of the war in Ukraine is the upward pressure international sanctions have had on fertilizer prices, which were already breaking records prior to Russia’s invasion. Many farmers have already made the switch to manure and other converts might soon be on the way – which makes it more important than ever for those selling and handling manure to follow best practices in order to keep that value high and help growers maximize yields while keeping costs low.

Storage, agitation, weather and timing all play key roles in getting the most from your manure this year. 

Applicators: Manage your time
Robb Meinen, senior extension associate with Penn State’s department of animal science, says the best time to apply liquid manure is when fields are dry, and when you can get on the field and operate without impacting the soil. “If you have adverse weather,” he says, “you have [an] increased risk of loss of nutrients because the weather or the soil [already wet or snow-covered or saturated], increases the risk of runoff.”

Wet soil, he adds, is more likely to become compacted if driven on, which further exacerbates the risk of runoff. That’s why he recommends keeping an eye on the weather forecast in order to plan ahead for a window of opportunity when both weather and soil conditions will be optimum for liquid manure application.

“The ideal weather would be a day when the soil conditions allow us to get on the field without compaction,” says Meinen, “and the predicted weather does not show us that we have an increased risk of loss.”

With summer ever-nearing and the remnants of snowmelt now gone, that might mean getting out on the field cast. According to John Lauzon, associate professor of soil management and soil fertility, University of Guelph, says the best time to apply liquid manure is in the spring.

“Liquid manures are primarily ammonium-N in terms of their nitrogen source,” he explains. “That ammonium can very quickly convert to nitrate, which can be lost. So if we apply that liquid manure in the fall, then there’s a very good chance that most of that ammonium-N is lost before the next growing season. Whereas if we apply it in the spring, then the chance of loss is much lower.”

Manure injection
Even with ideal weather and soil conditions, liquid manure is best applied with injection. Granted, manure injection can be more time-consuming (unless you have a drag line), and isn’t always practical or cost-effective, but it does help with the loss of nutrients. 

“Our goal, when we apply manure, should be to think of it as nutrient placement,” explains Meinen. “If we surface-apply manure, we expect there to be volatilization of ammonia immediately. That immediate volatilization is a loss of nitrogen, which goes into the air. Ways to hedge against that include manure injection, which places the manure beneath the soil surface, avoids that exposure to air, and conserves nitrogen so that it does not volatilize.”

 Another way to minimize volatilization, Meinen adds, is to apply the manure when it’s cold. “If we’re below 50F (10C), we expect there to be less volatilization of ammonia because the molecules are moving slowly,” he explains.

Best practices: agitation
The longer liquid manure sits in storage, the more it naturally stratifies, which is why agitation is essential in order to create a more homogenous mixture with a more uniform distribution of all the nutrients. The question then becomes: how much does one need to agitate?

“Every manure storage system is going to be a little bit different,” explains Meinen. “So it takes some skill, and this is where science is overtaken a little bit by art, because the person that has the equipment knows what their equipment is capable of doing. And then they also have to use their experience to do the job correctly.”

Meinen argues that over-agitation isn’t a concern, except for the fact that doing so wastes time and energy. 

You would over-agitate if you suspended all the solids and then you used more power and time and fuel to agitate when you didn’t need to,” he says.

Best practices: storage
If you’re hoping to make good money off of your cows’ manure, storage will be key to getting value. But the ideal storage system for liquid manure will be different, depending on where you are in North America. “We know that in any given region we will see manure storage systems that are typical for that region,” explains Meinen. “And there’s a reason why they are typical for their area: because they work well with the weather, and the cropping systems that are in that area.”

 When installing a new liquid manure storage system, Meinen advises a design that will prevent exposing workers or animals to deadly gasses.

“There are a lot of systems that store manure under the floor of a barn, right underneath the animals, and they work perfectly well because we can properly ventilate the system,” he adds. “So ventilation is key.”

Liquid manure valuation
Meinen says well-balanced nitrogen and phosphorus ratios are key to providing a valuable product. “In a typical scenario, if we apply manure at a nitrogen-based rate, perfectly matching the nitrogen we put into the field with what the crop needs, we will always over-apply phosphorus. But if we can conserve nitrogen during the application – by injecting the manure or applying it during colder days – we can make that ratio work in our favor.”

A key strategy for limiting nitrogen loss through volatilization is to limit the amount of time it stays in storage before it’s applied to the field.

“Another way to get more value is to apply the manure close to the time when the crop needs it,” adds Meinen, who points out that while you will lose some nitrogen in storage, that loss is sped up once the manure is applied to the field. “So if you apply the manure three months ahead of the crop uptake, chances are you’re going to lose more nitrogen than if you had held on to that manure for three months, and then applied it [closer to when it was needed].”

Do the math
Lauzon stresses the importance of limiting nutrient loss through best practices on the part of both the applicator and the grower. Ultimately as an applicator, Lauzon says, getting the job right the first time is critical, because the ideal is to reduce the need for the grower to eventually need to purchase more fertilizer and make up for the deficit.

“Growers will want to minimize loss in order to maximize the amount of nutrients that are left for the plant to use,” he explains. “If the value of your manure goes up, it means that when you have loss, the cost of that loss goes up too. So you’ll want to do some math: If I’ve lost X number of dollars per acre, in terms of manure value, how much would it have cost to change my manure management, to prevent that loss?

“And if the cost of changing that management is less than the value of the dollars lost in nutrients, then it becomes easy to justify for the grower on an economic basis.” •