In a unique research study, North Carolina State University and Oregon State University researchers have completed tree planting on an old, unused manure lagoon in North Carolina. The study is looking at an alternative way to close out inactive manure lagoons. Researchers will determine if it is an environmentally friendly and economical way to “decommision” a manure lagoon.
When a lagoon is closed in a conventional way, sludge is pumped out, hauled and spread on cropland, sometimes several miles away. That’s one reason why it costs an average of $43,000 per lagoon acre to close down a lagoon in North Carolina. The net cost of filling a lagoon and planting trees should be substantially less.
The two old lagoons that will studied are on a farm owned and operated by The Hanor Company. The lagoons were “retired” from service after a new, larger lagoon was completed.
The project’s first step was to pump free liquid from both lagoons, leaving sludge in the bottom of each. Then the lagoons were filled with soil and the tops are mounded.
Hybrid Poplar saplings ½ inch to 1 inch in diameter were planted on top of a 75-foot x 90-foot lagoon. The trees are bred for this purpose and are being used successfully in decommisioning landfills and other contaminated sites. The 320 saplings were planted in rows 12 feet apart, with 16 feet between the trees. This leaves space to add other tree species in the future. The young trees were planted 4 feet deep to promote nutrient uptake. Poplar roots develop at the surface and all the way down into the soil.
The trees will take up and remove nutrients from the sludge, producing marketable wood.
After trees are harvested, researchers say the ground can be used for pasture or another agricultural activity.
Monitoring wells are installed around each lagoon. The North Carolina Department of Environment and Natural Resources will monitor the wells as trees grow in order to check their impact on groundwater.
North Carolina State’s Animal and Poultry Waste Management Center and the North Carolina Pork Council are funding the study.