Research has demonstrated swine production's impact on watersheds can be minimized with technology and careful waste management practices.
Among other things, the University of Arkansas Swine Waste Demonstration and Training Project shows how two of the most important waste management concerns associated with swine production — excess phosphorus and buildup of manure solids in holding ponds — can be managed effectively.
Manure is typically flushed out of swine houses into holding ponds, or lagoons, until it is applied on crop or pasture land as fertilizer. When application is based on a crop's nitrogen needs, the land gets more phosphorus than the plants can take up.
“Excess phosphorus has become a problem in many areas of the state because it can run off into streams, ponds and lakes,” says animal scientist Charles Maxwell. “Reducing phosphorus levels in manure and managing it properly were key issues of this project.”
Maxwell's research has shown that phytase (a natural enzyme added to feed that decreases the need for calcium phosphate supplements) reduces phosphorus levels in swine manure.
“Phosphorus content was reduced about 25 percent in the lagoon that serviced the house in which the hogs were fed phytase,” says Maxwell.
The cost of phytase has come down to a level making it cost-effective. It is now widely used in Arkansas swine production.
Runoff was also reduced from fields where this manure was applied as fertilizer. “We still need to reduce phosphorus more when nitrogen is used as the basis for application,” Maxwell notes.
Other treatments being studied may help meet that reduction. Maxwell says aluminum chloride, a liquid compound, when added to manure before land application may bind phosphorus and make it less harmful to streams and lakes.
As for the buildup of manure solids in holding ponds, Extension engineer Karl VanDevender has shown that proper maintenance can prevent reduction of storage capacity.
“In Arkansas, holding ponds are typically designed to store manure and flush water for 180 days,” says VanDevender. “To remove the settled solids, the holding ponds are agitated to stir up the solids and remove them with the water. When this process is neglected, the settled solids build up over time and reduce water storage capacity.”
If allowed to continue, the reduction in liquid storage capacity increases the potential for overflows and point-source pollution.
A manure collection system built on a swine research farm near Savoy, Ark., features a settling basin in which waste solids settle out and are removed more frequently. VanDevender says the solid levels in the ponds were monitored using a Global Positioning System (GPS) to demonstrate how effectively agitation and pumping prevent buildup of solids.
“These practices maintain the effective storage capacities and prevent overflows and point source pollution,” he says. “Maintaining maximum storage capacity of the lagoons also eliminates the need for frequent land application, allowing the manure to be applied when the nutrients are needed and when risk of runoff is minimal.”
The demonstration project — funded by the Arkansas Soil and Water Conservation Commission — has been completed and results are being presented to swine producers.
Maxwell says the research will continue. “We want to continue gathering data that will help us refine management practices and test new technology to improve swine production and waste management.”