Getting the most from manure: Avoid phosphorus losses

Gloria Hafemeister
As farmers empty their manure storage pits in the fall, they are looking for ways to prevent nutrient losses and save wear and tear on roads by utilizing hoses.

Madison—According to Dr. Clinton Church, a researcher with the USDA Agricultural Research Service, no-till is not necessarily a benefit when considering phosphorus loss.

Speaking at the recent World Dairy Expo, Dr. Church said while no-till reduces soil run-off and soil carries phosphorus with it, the trade-off is that it causes problems when it comes to applying manure.

Dr. Church and others have researched various systems, including use of an aeration machine that drops manure in a sliced “pocket” just below the surface and a disk injection system that slices the soil, places the manure and then covers it with a closing wheel.

Researchers have also looked at using anti-leaching sweeps and pressure injection systems that blast manure under the surface.

When tillage is a part of the cropping system, many farmers broadcast manure, but he said the key to nutrient protection is immediate tillage following spreading the manure.

“The more manure that remains on the surface, the more nitrogen (ammonia) loss there will be and the more odor,” Church said.

While injection protects nutrients, he cautioned rain can take nutrients down into drain tiles if the conditions are right. That problem is minimized with anti-leaching sweeps that ride below the surface and turn the manure into the soil without disturbing the surface.

“All of the techniques are an insurance policy for runoff if a heavy rain would occur right after spreading manure,” he said.  “There are trade-offs with each system.”

Considering all these methods of managing manure without nutrient losses, Church posed the question, “What if manure didn’t have any phosphorus in it?”

He described a system that has successfully removed phosphorus in trials on several farms.

It begins by separating solids from liquid using an auger press. This removes 80 percent of the total solids, including 15 percent of the phosphorus, and leaves a material that is suitable as bedding material.

The remaining slurry then passes through a centrifuge press that removes more solids and phosphorus. These solids can then be transported to areas on the farm low in phosphorus.

The third step is a chemical treatment of the remaining slurry followed by moving the liquid through the Auto-Vac®, a rotary vacuum drum pre-coat filter that effectively removes solid particles from the sludge, producing dewatered dry waste.

“It takes 10 minutes to go through the entire system,” he said. “The final effluent has less than 1-percent solids and phosphorus, and the treated water is returned to the liquid manure storage.”

Church pointed out that the pH is unchanged in the process, and most of the nitrogen is retained.

As this process was being developed and tested on Pennsylvania farms, the researchers also looked at the economics of the system.

In their studies, the initial cost for a 1,000-cow herd is $750 per day or $180 per cow per year. That cost can be reduced to $125 per cow per year when reusing the solids for bedding.

When looking at the costs, Church said it could cost even less for farms that already have some of the components of the system, such as the solids-separator, in place. All these farms need to do is add the chemical and vacuum treatment.

Penn State has put in a patent request for the system, built by the USDA’s research team. The system is known as MAPHEX and is a mobile unit that is capable of serving 10 100-cow dairies on a rotation basis.

There are many ways farmers can use the system including selling nutrients to nurseries and gardeners, Church said. Nutrients from this system are also being used by a company that has designed “cow pots,” a flower pot made completely of dried composted manure solids that feeds plants as it slowly disintegrates.

That patented product was designed by a former dairyman, who Church said now makes more on the manure from his farm than the milk.