Photo: Steve Werblow
Manure management is a multi-layered challenge – a balance of biology, chemistry and physics, with an overlay of meteorology thrown in most years to complicate it further. Now a team in Mercer County, Ohio, is exploring whether the actual, physical layering of manure in hog house pits could help producers address those challenges.
The concept is straightforward. As manure sits, it stratifies. The solids settle to the bottom of the pit, leaving more of the water content closer to the surface. If the denser manure deeper in the pit turns out to be richer in nutrients, such as phosphorus, hauling a tanker load of it a few extra miles could become more worthwhile. It could improve the economics of transporting the manure farther from the hog operation, which may be surrounded by soils already enriched by previous manure applications.
The trick is determining whether the denser manure at the bottom of the pit indeed contains more nutrients. If so, there’s also the question of whether they can be effectively managed separately. The Mercer County Soil and Water Conservation District (SWCD) and Terry Mescher of the Ohio Department of Natural Resources (DNR) decided to find out. The team sampled 20 hog manure pits last spring and is currently analyzing the results.
Analysis of the 8-foot-deep pits – sampled at three levels – indicated significant variability in the nutrient content of manure at various depths. There were also major differences in the nutrient content under various hog houses, notes Terry Mescher, agricultural engineer with the DNR in Sidney, Ohio, who worked with the group from the SWCD.
“Ammonia nitrogen content was pretty consistent across the board, but there was an increased concentration of phosphorus of 50 to 90 percent in the bottom of the pit,” Mescher says. “There was a lot more variation between houses than we would have guessed there would be, even on the same farm. Comparing the pit with the least amount of phosphorus with the pit with the largest amount, we were looking at a two to two-and-a-half-fold increase.”
He says phosphorus levels ranged from 8 to 20 pounds per 1,000 gallons in the upper layers of the pits to 45 to 90 pounds of P per 1,000 gallons in the deeper layers. With that much P concentrated toward the bottom, the manure in the lower 2.5 to 3 feet of the pit may turn out to be worth hauling a longer distance. Mescher plans to study the economics this winter. In the meantime, he notes, “we definitely learned the importance of testing each individual pit on the farm.”
“We’ve had mixed reviews so far,” says Laura Walker, watershed coordinator for the Grand Lake St. Mary’s Watershed Alliance in Celina, Ohio. “Some people say, ‘it will never work.’ Some people want to give it a try. There are no answers across the board.”
Photo: Mercer SWCD
Walker points out that the pressure to manage manure pits more intensively is mounting as regulations narrow the window for application. Next year, local producers will be prohibited from applying manure to frozen ground, she says, and several people in the county have been investing in equipment to haul and even broker hog manure to distribute it more widely and make the most of the remaining application season.
Mescher says such challenges make a thorough look at the team’s data more important than ever.
“My goal,” he says, “is to build enough of this information to say to a producer, ‘this is the potential you’ve got here. How can we take advantage of this, or if you don’t have the ground to do it, how can somebody else take advantage of this potential?'"
This winter, a more thorough analysis of the sample data and collaboration with producers and manure haulers could help propel those discussions – and the answers may reflect a new understanding of the economics of hauling hog manure. Stay tuned.
For more information on this project, contact Laura Walker at (419) 586-3289 or firstname.lastname@example.org.