Direct Measurement of Denitrification Using 15 N‐labeled Fertilizer Applied to Turfgrass

Denitrification losses are a possibility from turfgrass because of frequent irrigation, multiple applications of N fertilizers, and an abundance of readily decomposable organic C in thatch and verdure. Field experiments were conducted to directly measure N 2 and N 2 O evolved from a Flanagan silt loam soil under Kentucky bluegrass ( Poa pratensis L.) or creeping bentgrass ( Agrostis palustris Huds.). Mass spectrometric procedures were used to analyze atmospheric samples collected from replicated 15 N fertilized turf (49 kg ha −1 ). Data showed that labeled fertilizer N (LFN) losses ranged from 2.1 to 7.3% for N 2 and from 0.4 to 3.9% for N 2 O; that large N 2 and N 2 O fluxes occurred after heavy rainfall events; and that more N 2 was evolved than N 2 O. Emission of gas was detected while standing water was visible within cylinders, suggesting the transfer of gases from the flooded soil to the atmosphere through the turfgrass plants. Evolution of N 2 and N 2 O was greater from creeping bentgrass treated with KNO 3 than urea through the first 3 wk of the experiment, whereas N 2 emission was greater for urea during the last 2 wk of the experiment, presumably because of NO 3 production through nitrification. Nitrous oxide was detected on the day of fertilization with the KNO 3 treatment, and the mole fraction of N 2 O decreased from 0.44 to 0.11 with each weekly application of N.