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TECHNICAL REPORTS

Nitrous Oxide Fluxes in Turfgrass

Effects of Nitrogen Fertilization Rates and Types

Dep. of Horticulture, Forestry & Recreation Resources, 2021 Throckmorton Hall, Kansas State Univ., Manhattan, KS 66506

^* Corresponding author (bremer{at}ksu.edu)

Urban ecosystems are rapidly expanding and their effects on atmospheric nitrous oxide (N₂O) inventories are unknown. Our objectives were to: (i) measure the magnitude, seasonal patterns, and annual emissions of N₂O in turfgrass; (ii) evaluate effects of fertilization with a high and low rate of urea N; and (iii) evaluate effects of urea and ammonium sulfate on N₂O emissions in turfgrass. Nitrogen fertilizers were applied to turfgrass: (i) urea, high rate (UH; 250 kg N ha^–1 yr^–1); (ii) urea, 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 N₂O were measured weekly for 1 yr using static surface chambers and analyzing N₂O by gas chromatography. Fluxes of N₂O ranged from –22 µg N₂O-N m^–2 h^–1 during winter to 407 µg N₂O-N m^–2 h^–1 after fall fertilization. Nitrogen fertilization increased N₂O 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 N₂O-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 N₂O 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 N₂O emissions in turfgrass ecosystems.

Abbreviations: AS, High rate of ammonium sulfate fertilization • DOY, day of year • PVC, poly-vinyl chloride • UH, High rate of urea fertilization • UL, Low rate of urea fertilization