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