By Jan Suszkiw, USDA-Agricultural Reserach Service

A mobile system for removing phosphorus from cow manure may offer dairy farmers greater flexibility in where, when, and how they use the nutrient to fertilize crops.

Manure can be spread onto crop fields as a source of phosphorus, nitrogen, and other nutrients important to plant growth. But applying too much manure can lead to excess phosphorus that ends up in lakes, rivers, ponds, and other water sources, degrading their quality.

The idea behind the Manure Phosphorus Extraction System (MAPHEX) is to remove the phosphorus and concentrate it in a form that's easier to manage, says Clinton Church, an Agricultural Research Service (ARS) environmental chemist at University Park, Pennsylvania—a state that boasts 531,000 milking cows and ranks fifth in the nation in dairy production.

Hauling manure off the farm to new field locations where it can be spread isn't always feasible. For example, "Some farmers with plenty of land may need to drive 20 miles or more to reach some fields. That makes transporting large volumes of manure uneconomical (or impractical), even if the crops there need phosphorus," notes Church, with ARS's Pasture Systems and Watershed Management Research Unit. Transporting concentrated phosphorus from the new treatment method would be far less costly.

Working with Pennsylvania State University collaborators, Church and his ARS colleagues developed and tested MAPHEX as a way farmers could not only "mine" phosphorus from their manure stores, but also market the nutrient as a value-added product.

To do this, the team mounted an auger press, centrifuge, vacuum-filter unit, and other components atop two trailer beds so that the entire system could be driven to a farm and operated onsite, either on a daily or rotational basis depending on the size of the dairy operation.

"In Pennsylvania, there are a lot of small dairy farms with 100 to 150 cows," says Church. "We made the system mobile so that we could service 10 small farms on a 10-day rotational basis." On a larger farm, like one with 2,000 cows, the system could operate over 24 hours, he adds.

MAPHEX works in three stages, each removing progressively smaller fiber particles and other phosphorus-containing solid matter from the manure. In addition, there is a chemical treatment step between the last two stages to convert dissolved phosphorus into a filterable particle. Water extracted from the manure is retained on the farm; it contains most of the manure's nitrogen, making it ideal for "fertigation"—fertilizing crops with irrigation methods.

MAPHEX works quickly. In about 10 minutes, for example, it can extract 99 percent of the phosphorus from 250 gallons of manure. Additionally, "it removes the odor from the manure, which is a big deal if that manure will be spread next to a town," adds Church.

The fiber and other phosphorus-containing particles exit the system as concentrated solids, which can then be transported for use on off-farm crop fields or sold to nurseries and other outlets as a plant and soil amendment. Solids from MAPHEX's first treatment stage could also be sold as cow bedding material, offering a lower phosphorus content and a lower risk of the nutrient's environmental escape than the manure solids-based bedding now used. Other possible uses include material for creating biodegradable pots, whose traces of the nutrient can help feed and sustain the plants seeded into them.

The MAPHEX team will begin demonstrating a full-scale version of its patent-pending system on a working dairy farm next spring and welcomes inquiries on its commercial potential.