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Corn+Soybean Digest

Corn and Soybean Producers and Dairies Benefit From Manure as Fertilizer

If you've got a large dairy barn near your grain farm, you might smell manure. Or you might smell “moo-lah.”

Dairy manure saved the Koehl family of Hancock, MN, at least $30/acre on fertilizer this fall compared to commercial nitrogen (N), phosphate and potash. And that doesn't count the value of the manure's micronutrients and organic matter.

The Koehls buy liquid manure from Riverview, a nearby dairy operation that milks about 30,000 cows at five sites.

In addition to saving money, “we see a yield benefit from manure, not only in the first year but in the following years, too,” says Mitch Koehl, who raises corn for grain and silage, wheat, kidney beans and alfalfa with his dad, uncles and cousins. The seven-family group also operates a feed supply business, three swine finishing barns and a cattle feed-lot. Despite having their own manure source, “we'll take as much dairy manure as we can get,” Koehl says. “It's an economic advantage for us.”

About 5% of U.S. cropland is fertilized with manure, according to a June 2009 report to Congress by the Agriculture Department. But higher fertilizer prices this decade — and the likelihood of future price hikes — have boosted interest in manure, says Eric Dresbach of Circleville, OH, president of the Midwest Professional Nutrient Applicators Association.

Riverview barns, for example, generate enough manure to fertilize more than 22,000 acres of corn ground a year, yet “our list of guys who want manure is longer than we can supply,” says Brad Fehr, Riverview agronomist. The dairy furnishes low-cost fertilizer to about 50 local growers, he says.

Meanwhile, expanded environmental regulation and “more big barns on little farms are driving the need for a larger land base to apply manure,” Dresbach says.

More manure for sale or exchange is a “great advantage for crop producers,” he says. “If I had a livestock producer near my farm, he'd be my best friend.”

Koehl seconds that: “As crop producers, the dairy is a real benefit for us, both as a place to sell crops and as a source of fertilizer.”

The Koehl family farms land near three of Riverview's dairy barns in west-central Minnesota.

RIVERVIEW SEPARATES MANURE and sends the solids back to the barns for bedding. The liquid manure, which contains about 4% solids, is stored in tarp-covered basins. In the fall, Riverview pumps the fertilizer through hoses to fields up to three miles away, where it's injected into the soil with a tractor that pulls a dragline hose through the field.

Dragline hose application systems cut liquid manure transportation costs and reduce compaction, which is a big concern for grain farmers who receive manure, says Kevin Erb, a University of Wisconsin Extension manure specialist. “A 9,500-gal. manure tanker plus a tractor can weigh 150,000 lbs., which can be a problem in wet soils.”

Riverview takes frequent nutrient samples throughout the pumping period. Crop farmers worry about erratic nutrient ratios in manure, Fehr says. It's one reason manure gave way to commercial fertilizers. But thanks to covered basins and other management practices, “we see little nutrient variation. It's a very consistent product.”

This fall the Koehls bought 700 acres' worth of Riverview manure. On corn silage and dry edible bean fields, the liquid is injected directly into crop stubble. On corn grain and wheat fields, “we work the ground first, then inject manure,” Koehl says.

Because their land is regularly receiving manure, the Koehls soil test most fields every fall. Their soils score in the medium range for phosphorus (P) and potassium (K), allowing the manure rate to be formulated on an N basis. Their typical application supplies about 135 lbs./acre of N available the first year, 65 lbs. P, 200 lbs. K and 3 lbs. zinc. “We don't add any additional fertilizer, except some anhydrous on the end row where they turn the applicator,” he says.

The dairy manure they bought this fall provided nutrients worth at least one-third more than the manure cost, Koehl says. USDA reports that corn growers who substituted manure for commercial fertilizer lowered their fertilizer expense by 37% compared to farmers who used commercial fertilizer only.

THE BENEFITS OF manure for crop yields and soil are well documented, but cash grain farmers should carefully weigh the economics, Erb says. Manure application costs, which are determined by time and distance, may exceed the value of the nutrients, especially with liquid dairy manure. He says, “Manure can pay a big dividend, it can be a break-even or it can cost more than commercial fertilizer. It depends on your location, soil tests and the cost of commercial nutrients.”

Still, says Dresbach, “When we think about the value of manure, it's more than N, P and K. You also get the micronutrients, the microbial activity and the organic matter. These are worth as much as the N, P and K.”

Manure improves soil tilth and moisture-holding capacity, too, Koehl adds — even the liquid portion. Plus, “putting manure back on the fields really helps with compaction problems” resulting from chopping and loading corn silage.

“Mechanical separators don't remove all the organic matter,” Erb says, typically leaving nearly half the solids.

In 2008, when commercial fertilizer prices skyrocketed, Dresbach's phone rang off the hook with grain farmers asking for manure. Some crop producers were even willing to pay all the application costs, “and pay the livestock producer something for the nutrients,” he says.

This year, with lower N and P prices, crop and livestock producers are more likely to share application costs 50-50 or 40-60, he says. It's a good deal for crop producers, who often are getting “half-price fertilizer.”

Besides that, Dresbach adds, “We're saving resources.” Nearly two-thirds of corn growers who apply manure reduce their commercial N applications by more than half, USDA reports. “We're the original recyclers.”

A Minnesota milk producer is getting more than fertilizer from manure. Riverview, a multi-family enterprise in Stevens County, is among the first large Midwest dairy farms to install manure digestion. The company is turning raw waste from 13,500 dairy cows into renewable electricity, livestock bedding and less-smelly fertilizer.

Manure digesters capture methane, a natural gas substitute that can be burned for heat or electricity. A year ago, Riverview began operating digesters at two of its west-central Minnesota dairy barns. The digesters are 16-ft.-deep enclosed cement tanks, mostly underground. Liquid manure flows from the barns to the chambered tanks, where it's heated to 100° F for 21 days. As manure moves through the digesters, a natural microbial process generates bio-gas composed of carbon dioxide and methane. The methane fuels on-site electrical generators.

Riverview's two manure digesters produce 2.4 megawatts of electricity — enough renewable energy to supply about 2,400 homes, says Kevin Wulf, a Riverview spokesman. The green power is sold to a local electric cooperative.

The effluent from the digesters is mechanically separated into solids, which are recycled for cow bedding and liquid fertilizer.

Digested dairy manure retains all its nutrients and some of its carbon, says Carrie Laboski, a University of Wisconsin Extension soil scientist. But there hasn't been much research yet comparing the agronomics of raw vs. digested manure, she says.

Laboski's lab studies suggest that the liquid fraction of digested, separated manure may have more nitrogen avail-able to plants the first year, increasing manure's value. That hasn't been verified in field studies, though, she notes.

Phosphorus (P) tends to segregate in the solid fraction of separated manure, so the amount of P applied to fields in the digested liquid portion is lower than for raw manure, she says. Digestion probably doesn't affect potassium availability.

Limited research suggests that digestion may reduce — but not eliminate — pathogens in manure, says David Schmidt, a University of Minnesota engineer. Research on how digestion affects weed management is also just beginning, he says. In a recent Minnesota field study, digestion had little effect on total weed seed germination, although first-year germination of velvetleaf was accelerated, compared to raw manure.

Well-managed digestion does reduce offensive manure odors, Laboski says. “That's a huge community benefit.”

And manure digestion has other environmental and social benefits, says Riverview's Wulf. It captures methane, a potent greenhouse gas, preventing release into the atmosphere. And renewable methane replaces fossil fuels.

That's part of what motivated Riverview's investment in manure digestion, he says. Using this technology to make green energy, reduce manure odor and preserve the land's productivity “fits with our company's values.”

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