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Pollution control

On a call to a customer's dairy farm, Thomas Huffman, president of a company that makes manure-pumping systems, looks to the north a half-mile and sees a big chicken farm. A half-mile to the east, there's a large pig finishing operation. Scanning the landscape and an increasingly complex book of regulations, Huffman sees trouble ahead: There's too much manure, not enough land to spread it on, and looming EPA directives on phosphorus that could soon make it all worse.

“On some acres we won't be able to apply any manure at all,” Huffman says. “On others, we may find ourselves using a 40-ft. toolbar to knife in such small amounts of liquid manure that it will barely make the soil wet.”

EPA has identified phosphorus (P) runoff as the primary surface water pollutant to cause massive algae blooms and eutrophication that leads to fish kills.

Under the new EPA phosphorus-based regulations, scheduled to change later this year, the P content of manure, combined with how much P already exists in the soil, will determine how much manure can be spread on an acre of land. Even though EPA is set to target the P from swine manure first, similar regulations on poultry, dairy and beef will follow in sequential years.

Manure transport

Huffman's company, Hydro Engineering, specializes in selling manure-pumping systems to large-scale livestock operators. The system can push manure through mile-long tubes over and/or under the ground. Connected directly to a hose-drag manifold system mounted behind a tractor, pumping can be quicker and easier than hauling the manure in tanks, trucks or spreaders. Huffman estimates the $60,000 to $160,000 system makes economic sense for operators who need to move more than 1.5 million gallons of manure in a year, the typical amount produced by a 250 dairy cow herd or a 13,000 pig/yr. finishing operation.

For Huffman and his customers, the bottom line is that the new regulations will require twice as much land for the same amount of manure. That could mean pumping through a hose two miles long instead of one.

“Farmers have to apply manure thinking in terms of nutrient management,” he says. “The amount of N and P applied will need to roughly match the amount taken out by the crop.”

In many cases, the issue of fertility is virtually ignored. It's more a matter of just finding enough land to spread the manure on. In eastern Wisconsin, for example, Huffman is seeing soil P levels increase 15 to 20 lbs. each year. A 1,200-head dairy farm produces about 12 million gal. of manure/yr. With the average dairy farm applying 10,000 to 15,000 gal./acre, the crop just can't take up the nutrients fast enough.

Phytase pays

One solution may lie with the enzyme phytase. Plants store P as phytic acid, but animals have a hard time digesting this form of P. As a result, most plant-based P passes through an animal's gut and is excreted in manure where it can become a water pollution concern. Meanwhile, producers must add supplemental P to the ration in order to meet the animal's nutritional needs.

Phytase can be fed to animals to help them digest phytate or phytic acid. Scientists have known since the late 1960s that adding phytase to swine feed enables animals to digest more of the P in feedstuffs. However, phytase was impractical to produce for routine use until the 1990s, when new technologies allowed large-scale production.

Today, by using phytase, manure P levels often are reduced by 30 to 35%, at a cost that is slightly lower than the supplemental P that the phytase replaces.

Jon Wilson of phytase supplier Roche says replacing some of the inorganic supplemental P with his company's product, Ronozyme P, actually saves money. “It's a case of X units of phytase replacing X units of P,” Wilson says. “Depending on the price the producer pays for his P and for the phytase, it's reasonable to expect a savings of 50 cents to a dollar per ton of feed by using phytase. This works because the animals are able to digest considerably more of the P that would otherwise be unavailable in its phytic acid plant form.”

Performance identical

Recent studies at the University of Nebraska and Virginia Polytechnic Institute and State University show that phytase can replace approximately 0.1 percentage point of inorganic P in swine rations (the level recommended by phytase manufacturers) without affecting swine performance.

The studies also show that swine performance is virtually identical with two major commercial phytase enzyme brands: Ronozyme P from Roche and Natuphos from BASF. “We could detect no difference between [phytase] products in terms of the amount of P they could replace,” says University of Nebraska Extension specialist Mike Brumm.

“In Nebraska, we have gone from 10 to 15% of herds using phytase to something just less than a majority. I expect continued growth in the use of phytase over the next year or two,” Brumm says.

Low-phytate grain

In the late 1990s, seed companies appeared to offer the best hope for reducing P in manure. The hoped-for solution was a low-phytate (low phytic acid) corn hybrid.

At first, results were encouraging. The P in low-phytate corn was three to four times more bioavailable to livestock than the P in conventional corn. Feeding low-phytate corn, and reducing supplemental P, reduced P excretion in manure by up to 40%. But there was a problem — yield. Pioneer Hi-Bred, ExSeed Genetics and other seed companies attempted to bring low-phytate corn hybrids to market. Yield of the low-phytate inbreds was too low to make low-phytate hybrids economically viable for corn growers.

It turns out that phytic acid is required for proper plant function. “Eliminating all phytic acid in a hybrid prevented germination of the seed,” says Kim Kuebler of ExSeed.

Douglas Yungblut, a nutritionist with Pioneer Hi-Bred, says the digestibility of low-phytate grain is excellent, but adds, “The most recent agronomic developments in low-phytate corn are not very encouraging.”

To date, no seed company has been able to break the low-phytate yield barrier. An independent 2001 study by the University of Minnesota concluded that low-phytate lines of corn produced 12% less yield than conventional lines of corn. Nevertheless, Kuebler says ExSeed expects to produce marketable low-phytate hybrids within the next two to five years, hopefully with higher yields.

Settling research

Another solution to the P problem may be to separate P out of the manure into solids. Municipal waste treatment facilities have successfully reduced P content in liquid waste by adding calcium. Calcium reduces acidity (raises the pH) and binds to P to form calcium phosphate. The result is a form of P that readily settles out into solids.

Jun Zhu, engineer with the University of Minnesota Extension Service, realized it would be difficult to convince most hog farmers to spend money adding calcium to manure. Could there be a less expensive way to raise pH? Mixing manure to release carbon dioxide raises pH but requires considerable energy and disturbs the solids. Zhu's solution: Bubble some air through the mixture. The pH goes up, and the calcium that already naturally exists in the manure binds to the P.

“While the process is still in the experimental stages, our results are very encouraging,” Zhu says. “Most of the P settles out into solids, which accounts for only 2 to 7% of the total manure volume. That amount is much easier to haul away. And by cycling the pump on and off, the process is very energy efficient.”

Zhu found that with both intermittent (on and off every 2 hrs.) and continuous aeration, the manure pH increases by about one unit, from 6.5 to 7.5, within one day. This increase in pH is accompanied by a 75% reduction in soluble phosphorus concentration in the liquid manure.

Zhu's research to date has involved small-scale experiments, which run an air hose to the bottom of a PVC pipe full of manure. He is now conducting large-scale testing at the university agricultural experiment station in Waseca, MN.

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