July 21, 2009

Study shows manure no worse for water in tiled fields

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.

Writer: Brian Wallheimer, 765-496-2050, bwallhei@purdue.edu

Sources: Ronald Turco, 765-494-8077, rturco@purdue.edu

Sylvie Brouder, 765-496-1489, sbrouder@purdue.edu

Ag Communications: (765) 494-8415;
Steve Leer, sleer@purdue.edu
Agriculture News Page

Artificial subsurface drainage is commonly used in midwestern agriculture and drainage losses of dissolved organic carbon (DOC) from such systems are an under-quantified portion of the terrestrial carbon (C) cycle. The objectives of this study were to determine the effect of common agricultural management practices on DOC losses from subsurface tile drains and to assess patterns of loss as a function of year, time of year, and drainflow. Daily drainflow was collected across six water years (1999–2004) from a restored prairie grass system and cropping systems which include continuous corn (Zea mays L.) and corn-soybean [Glycine max (L.) Merr.] rotations fertilized with urea-ammonium-nitrate (UAN) or swine (Sus scrofa) manure lagoon effluent. The DOC concentrations in tile drainflow were low, typically <2 mg L–1. Yearly DOC losses, which ranged from 1.78 to 8.61 kg ha–1, were not affected by management practices and were small compared to organic C inputs. Spring application of lagoon effluent increased yearly flow-weighted (FW)-DOC concentrations relative to other cropping systems in three of the years and increased monthly FW-DOC concentrations when drainflow occurred within 1 mo of application. Drainflow was significantly and positively correlated with DOC loss. Drainflow also affected DOC concentrations as greater 6-yr cumulative drainflow was associated with lower 6-yr FW-DOC concentrations and greater daily drainflow was associated with higher daily DOC concentrations. Our results indicate that lagoon effluent application and fertilizer N rates do not affect long-term losses of DOC from tile drains and that drainflow is the main driver of DOC losses.

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