Nitrous oxide fluxes in turfgrass: Effects of nitrogen fertilization rates and types

Urban ecosystems are rapidly expanding and their effects on atmospheric nitrous oxide (N[subscript]2O) inventories are unknown. Our objectives were to: 1) measure the magnitude, seasonal patterns, and annual emissions of N[subscript]2O in turfgrass; and 2) evaluate effects of fertilization with a high and low rate of urea N; 3) and urea and ammonium sulfate; on N[subscript]2O emissions in turfgrass. Nitrogen fertilizers were applied to turfgrass: 1) urea, high rate (UH; 250 kg N ha[superscript]-1 yr[superscript]-1); 2) urea, low rate (UL; 50 kg N ha[superscript]-1 yr[superscript]-1); and 3) ammonium sulfate, high rate (AS; 250 kg N ha[superscript]-1 y[superscript]-1); high N rates were applied in five split applications. Soil fluxes of N[subscript]2O were measured weekly for one year using static surface chambers and analyzing N[subscript]2O by gas chromatography. Fluxes of N2O ranged from 22 [Greek letter mu]g N[subscript]2O-N m[superscript]-2 h[superscript] -1 during winter to 407 [Greek letter mu]g N[subscript]2O-N m[superscript]-2 h[superscript] -1 after fall fertilization. Nitrogen fertilization increased N[subscript]2O emissions by up to 15 times within three days although the amount of increase differed after each fertilization; increases were greater when significant precipitation occurred within three days after fertilization. Cumulative annual emissions of N[subscript]2O-N were 1.65 kg ha[superscript -1] in UH, 1.60 kg ha[superscript] -1 in AS, and 1.01 kg ha[superscript]-1 in UL. Thus, annual N[subscript]2O emissions increased 63% in turfgrass fertilized at the high compared with the low rate of urea, but no significant effects were observed between the two fertilizer types. Results suggest that N-fertilization rates may be managed to mitigate N[subscript]2O emissions in turfgrass ecosystems