A Decade of Nitrogen Leaching from a Kentucky Bluegrass (Poa pratensis L.) Turf.

Nitrogen fate research was initially conducted at Michigan State University in 1991.  The initial research conducted from 1991 through 1993 indicated that there was minimal risk of nitrate-nitrogen leaching from turfgrass.  Since the summer of 1998 percolate samples have been collected from the same monolith lysimeters and analyzed for nitrate-nitrogen.  As of 2008, the turfgrass area has now been under continual fertilization practices for 18 years with percolate collection for the last ten years consecutively.  From 1998 through 2003 two nitrogen rates were analyzed: 245 kg N ha^-1 and 98 kg N ha^-1.  Since 1998, NO₃-N concentrations in leachate for the low N rate have typically been below 5 mg L^-1.  From 2000-2002, for the high N rate, NO₃-N concentrations in leachate were often greater than 20 mg L^-1.  In 2003 the high N rate was reduced to 198 kg N ha^-1 but the concentration of NO₃-N leaching from the high N rate treatment did not decline from the previous years.  In 2004, the concentration of NO₃-N leaching from the high N rate treatment declined drastically from previous years.  The average concentration of NO₃-N in leachate for the high N rate from 2004 through 2006 was 11.1 mg L^-1, which was a significant decline from the average concentrations observed for the high N rate from 2000 through 2003.  In 2007, the  mean NO₃-N concentration in leachate for the high N rate was 4.9 mg L^-1.  This was a decrease in NO₃-N leaching from 2006 of approximately 7 mg L^-1.  This was the lowest mean NO₃-N concentration in leachate for the high N rate since data collection began in 1998.  This research indicates that leaching potential from continually fertilized turfgrass sites changes as the site matures.