Applying swine manure to a tiled field has no more carbon impact on nearby waterways than other fertilizer systems, according to a Purdue University study reported in the Journal of Environmental Quality.
Ron Turco and Sylvie Brouder, Purdue agronomy professors, reviewed six years of drainage data and found that effluent from swine lagoons when applied to tiled cropland did not increase carbon levels entering nearby waterways. "It was surprising in a way that carbon loads were relatively low at the discharge points," Brouder said. "The assumption was that manure was adding significantly." Lagoon effluent contains a high amount of carbon.
Because tiles are used to direct excess water out of the soil and, eventually, into nearby waterways, there's been concern that tiles flush manure components, such as dissolved carbon, into water systems faster, thereby damaging water quality.
Carbon is a particular concern because bacteria, such as E. coli, consume carbon. Adding carbon to a stream could enhance microbial growth, including harmful bacteria. "In general, we didn't see more carbon in manure systems, but rainfall near an application event did promote some movement," Turco said. He added that the nitrogen data is still being reviewed.
The USDA-funded study involved measuring carbon emissions from 1999 to 2004 at the Purdue Water Quality Field Station. It included four blocks of 12 plots each with different crop rotations and varied fertilizer-application practices.
Turco's and Brouder’s next project is to evaluate how antibiotics and hormones from manure are transferred to streams through tiled fields.
Source: Purdue University