Tile drainage is an agriculture practice that removes excess water from soil subsurface to enable farming in wetlands. Whereas irrigation is the practice of adding additional water when the soil is naturally too dry, drainage brings soil moisture levels down for optimal crop growth.
Tile drainage ditch (Credit: Todd Royer)
A new paper in the Journal of Environmental Quality by Mark B. David, Laurie E. Drinkwater and Gregory F. McIsaac, Sources of Nitrate Yields in the Mississippi River Basin confirms that the run-off Nitrates from farming in the Missisipi river basin into the Gulf of Mexico leads to seasonal hypoxia. In the summer of 2010 this dead zone in the Gulf spanned over 7,000 square miles. The increased production of crops in this region for ethanol production has only exacerbated the problem. The dead zone in the gulf is a yearly event to be compared to those caused by sporadic oil spills.
Gulf areas affected by hypoxia: NOAA
(Journal of Environmental Quality 2010 39:1657-1667) via EurekAlert
Tile drainage in the Mississippi Basin is one of the great advances of the 19th and 20th centuries, allowing highly productive agriculture in what was once land too wet to farm. In fact, installation of new tile systems continues every year, because it leads to increased crop yields. But a recent study shows that the most heavily tile-drained areas of North America are also the largest contributing source of nitrate to the Gulf of Mexico. Scientists from the U of I and Cornell University compiled information on each county in the Mississippi River basin including crop acreage and yields, fertilizer inputs, atmospheric deposition, number of people, and livestock to calculate all nitrogen inputs and outputs from 1997 to 2006. For 153 watersheds in the basin, they also used measurements of nitrate concentration and flow in streams, which allowed them to develop a statistical model that explained 83 percent of the variation in springtime nitrate flow in the monitored streams. The greatest nitrate loss to streams corresponded to the highly productive, tile-drained cornbelt from southwest Minnesota across Iowa, Illinois, Indiana, and Ohio.
Farmers are not to blame,” said University of Illinois researcher Mark David. “They are using the same amount of nitrogen as they were 30 years ago and getting much higher corn yields, but we have created a very leaky agricultural system. This allows nitrate to move quickly from fields into ditches and on to the Gulf of Mexico. We need policies that reward farmers to help correct the problem. A lot of people just want to blame fertilizer, but it’s not that simple,” David said. “It’s fertilizer on intensive corn and soybean agricultural rotations in heavily tile-drained areas. There is also an additional source of nitrogen from sewage effluent from people, although that is a small contribution. It’s all of these factors together.”
Tags: Dead zones, Gulf of Mexico, hypoxia, nitrates, Tile drainage
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