Fifteen Years of Nitrogen Leaching from a Kentucky Bluegrass Turf

Abstract

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−1yr−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.