Fifteen Years of Nitrogen Leaching from 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.  Subsequent years of research on the same lysimeters indicate the risk of nitrogen leaching changes as the turf ages.  Since the summer of 1998 percolate samples have been collected from the same monolith lysimeters and analyzed for nitrate-nitrogen.  As of 2014, the turfgrass area has now been under continual fertilization practices for 24 years with percolate collection for the last 16 years consecutively. From July 1998 through 2002, lysimeters were treated annually with urea at a low N rate 98 kg N/ha and a high N rate 245 kg N/ha. In 2003 the N rate was reduced to 196 kg N/ha for the high N rate while the low N rate remained at 98 kg N/ha. During the first year (2003) of reducing nitrogen application rates from 245 to 196 kg N/ha there was no reduction in nitrate-N concentrations in leachate.  However, after 12 years of annual 196 kg N/ha applications there was a significant and sustained reduction in the amount of nitrate-N leaching to the point that the mean leaching concentrations are now lower than when the research was initiated in 1998.  This research has demonstrated the importance of long-term nutrient fate studies and improved our understanding of changes in nutrient fate due to the age of turfgrass site and annual nitrogen rate.