In these difficult economic times, it’s important for dairy producers to get the most out of their soil nutrients—both on and off the farm. Carrie Laboski, associate professor and Extension soil scientist with the University of Wisconsin-Madison, says whether nutrient needs are being met by manure varies with the size of the farm and its cropping pattern. “It’s not really a ‘one size fits all’ approach,” she says. “In some cases, they may have adequate phosphorus in their manure to go on to fields. Often, we have soil test levels that have been built up over time from repeated manure application so we don’t necessarily need a lot of that, when manure can meet those needs.”
Potassium is another matter. Laboski says farms with typical rotations of 3-4 years of hay followed by a couple of years of corn silage often don’t get enough potassium from manure alone, particularly when high-yielding alfalfa and corn silage are being grown. “Then,” she adds, “depending on how much corn ground they have and also the amount of manure they have, they may or may not need to purchase nitrogen for some of their corn.”
Laboski says there are management techniques farmers can use to maximize what they get out of their manure and reduce their need to spend precious cash on commercial fertilizers. Some producers, she says, have told her they believe they get the best results by applying all their manure to their corn ground, but that’s not necessarily the case. “I’ve gone through some of our research data from across the state,” she says, “the corn and alfalfa yields with nitrogen and potassium applications, and I think for some of these folks that they might actually be better off putting some of their manure on hay ground.” She concedes a lot of farmers don’t like to apply manure to standing hay, but says it can be valuable to get some potassium to the hay crop immediately following a cutting.
That means the nitrogen from that manure is not getting to the corn, but Laboski says the loss to the corn is often not enough to make a significant impact. “In one scenario that I ran,” she says, “we might expect that we’d have a 0.5-1.0 ton yield increase in the alfalfa if the soil test K level was optimum, and the alfalfa also needed a little bit of sulfur.” She says the value to the hay can be up to $120/acre, while the loss to the corn might be five bushels an acre—less than $20/acre.
But Laboski is mindful that the decision on manure applications may not be entirely up to the farmer. “If they’re under nutrient management plans and regulations, and that varies state by state, they might not be able to abandon a particular plan,” she says. But, “if they don’t have a plan, or if they have flexibility in the plan, they might be able to divert manure a little bit differently than how they originally planned; that might prove to be more beneficial in the long run.”
Wisconsin’s manure management plans, like those of other Upper Midwestern states, utilize a phosphorus index; applications are limited based on the potential for delivering P to surface water bodies. Applications of manure to legumes like alfalfa are also limited based on nitrogen uptake. “You cannot apply more manure than the amount of N that is removed by that crop in a year,” says Laboski. “So even though the legume doesn’t need the nitrogen, you can still put manure on that contains nitrogen, but you just can’t put it in excess of what’s going to come off the field.”
Some dairy farms, typically mid to very large operations, have adequate storage and can limit manure applications to the spring and fall. But many put it out as quickly as they gather it up. “There’s a farm I drive by,” Laboski says. “Nearly every day they’re applying liquid manure in the wintertime; they fortunately have very flat fields, so they probably don’t have much issue with their runoff. Others have solid manure that’s being stored maybe a day or two at a time, and then they’re going out all winter.”
Wisconsin Extension does not have recommendations on manure application timing relative to credits received, but she says, “The biggest impact would probably be on nitrogen, and in general for nitrogen management in the fall. If you can wait until it’s less than 50º F and incorporate it that would be best as far as minimizing losses. But we know when you’ve got a lot of manure to put down, you can’t always wait that long; it’s not practical. So some manure might go out even in early September after they’ve taken corn silage off, and the nitrogen credits from that manure are likely a little different than they would be for spring-applied manure.”
How much different, Laboski doesn’t know, but she’s hoping to find out. “I’m trying to obtain some funding to look at timing of manure applications—early fall, late fall, spring—and their effect on the following year’s nitrogen credits. And the second year’s nitrogen credits as well, because nitrogen tends to have credits beyond that first year.” The differences caused by application timing can be dramatic from year to year; the cool spring of 2009 produced fall-fertilized corn fields that, she says, “looked quite a bit better, actually, compared to where we had the spring manure applications. I think what was happening was with the fall manure application, there was still a little bit of warmth and some of the manure started breaking down and leaching nitrogen, whereas with the spring application it stayed cool at all times so we really didn’t have any mineralization of nitrogen from the manure.” Learning how much of an impact those differences present could be valuable knowledge to farmers hoping to improve their profitability, in addition to contributing to an environmentally sounder operation.
UWM is also researching the relative nutrient value of manure that’s been through an anaerobic digester; the number of the energy-generating devices on Wisconsin dairy farms has been growing, and the technology now offers several means of separating components. “I’ve done some preliminary lab work that suggests that the nitrogen availability out of these treated manure can be a fair bit different than a raw manure,” Laboski says. “We need to have a little more data behind that to give growers an idea of how they should take nutrient credits in those situations.”
Regardless of when or how producers spread manure, they need to know the federal and state regulations on applications in their area. Laboski says, “In some states, there may be some restrictions on applications in the late winter/early spring during the thaw. Some of the worst runoff issues we’ve had in Wisconsin have been where we’ve had that big snowmelt, and manure applications that went on just prior to the snowmelt and the ground thawing--that can be problematic. If you’re in areas where there’s snow, think about how close you are to waterways. It’s somewhat common sense, too, not applying right up to a stream, and in some cases the state tells you if you can or can’t do that. So you’re kind of balancing our water quality with getting manure out there on the land.”