Fifteen Years of Nitrogen Leaching from a Kentucky Bluegrass Turf

Most research on nitrate-nitrogen (NO3-N) leaching in turfgrass was conducted on recently established sites and indicates that leaching poses little risk to the environment. The potential for greater NO3-N leaching from mature turf sites is relatively unknown. Nitrogen (N) leaching from a Kentucky bluegrass (Poa pratensis L.) turf was measured for 15 yr using monolith lysimeters. From 1998 through 2002, half of the lysimeters were treated annually with urea at a high rate of 245 kg N ha(-1) (49 kg N ha(-1) application(-1)) and half of the lysimeters were treated at a low rate of 98 kg N ha(-1) (24.5 kg N ha(-1) application(-1)). Flow-weighted mean NO3-N concentrations in leachate for the low N rate were below 5 mg L-1 for every year but one of the 15 yr of research. For the high N rate, NO3-N concentrations in leachate for many dates from 2000 through 2002 were higher than the drinking water quality maximum contaminant level of 10 mg L-1. Due to high concentrations of NO3-N in leachate, the high N rate was reduced from 245 to 196 kg ha(-1)yr(-1) in 2003. From 2004 through 2013, there was a decline in NO3-N leaching. For both N rates, the flow-weighted mean NO3-N concentration in 2013 was less than in 1998, when the research was initiated. This research indicates that, as a turfgrass system ages, there is a critical annual N rate, above which NO3-N concentration in leachate may exceed the maximum contaminant level, and below which there is minimal risk.