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.”