Purdue Compares Manure, Fertilizer Applications

Applying manure to a tiled field doesn't have a negative effect on nearby water -- in terms of carbon -- when compared to other fertilizer systems, according to a Purdue University study.

Using six years of drainage data, Ron Turco and Sylvie Brouder, both professors of agronomy, found that the use of swine manure lagoon effluent in a tiled agricultural field did not increase carbon getting into nearby waterways. The results of their study were detailed in a recent issue of the Journal of Environmental Quality.

"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."

Tiles set below the surface of agricultural fields direct excess water out of the soil and, eventually, into a nearby stream. There has been a concern that tiles flush manure, manure components such as dissolved carbon, or other soil nutrients into water systems faster, damaging water quality.

Carbon is a concern because bacteria, such as E. coli, consume carbon. Adding carbon to a stream could improve conditions for microbial growth, including harmful bacteria. Manure lagoon effluent, the liquid formed and used as fertilizer after manure is stored in lagoons, contains a high amount of carbon.

"In general, we didn't see more carbon in manure systems, but rainfall near an application event did promote some movement," Turco said. "However, we didn't see a huge fluctuation out of any of these agricultural systems, but we are still looking at the nitrogen data."

Turco and Brouder, along with former graduate student Matt Ruark, measured the carbon emissions from 1999 to 2004 at the Purdue Water Quality Field Station, a research facility that allows scientists to study the effects of farm management practices on water quality. The study included four blocks of 12 plots each with different crop rotations and varied fertilizer-application practices.

Carbon emission into streams was the same in tiled fields fertilized with manure as in tiled fields using other sources of fertilizer. The amount of carbon reaching waterways increased in all fields during years with higher rainfall totals.

"We saw a few blips, things where there was a heavy rain after a manure application, but nothing that was statistically significant," Turco said.

The U.S. Department of Agriculture funded Turco and Brouder's research. They said the next step is to evaluate how antibiotics and hormones from manure are transferred to streams through tiled fields.

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