Denitrification in Suburban Lawn Soils

• Published in: Journal of environmental quality Vol. 40; no. 6; pp. 1932 - 1940
• Main Authors: Raciti, Steve M., Burgin, Amy J., Groffman, Peter M., Lewis, David N., Fahey, Timothy J.
• Format: Journal Article
• Language: English
• Published: United States The American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc 01.11.2011; American Society of Agronomy
• Subjects: Aquatic ecosystems; Budgets; Carbon Dioxide - metabolism; Denitrification; Ecosystem; Environmental Monitoring; Fertilizers; Forest soils; Growing season; Nitrates; Nitrogen; Nitrogen - chemistry; Oxygen - metabolism; Poaceae - physiology; Saturated soils; Soil - chemistry; Vegetation; Water Pollutants, Chemical - chemistry
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq2011.0107

There is great uncertainty about the fate of nitrogen (N) added to urban and suburban lawns. We used direct flux and in situ chamber methods to measure N2 and N2O fluxes from lawns instrumented with soil O2 sensors. We hypothesized that soil O2, moisture, and available NO3− were the most important controls on denitrification and that N2 and N2O fluxes would be high following fertilizer addition and precipitation events. While our results support these hypotheses, the thresholds of soil O2, moisture, and NO3− availability required to see significant N2 fluxes were greater than expected. Denitrification rates were high in saturated, fertilized soils, but low under all other conditions. Annual denitrification was calculated to be 14.0 ± 3.6 kg N ha−1 yr−1, with 5% of the growing season accounting for >80% of the annual activity. Denitrification is thus an important means of removing reactive N in residential landscapes, but varies markedly in space, time, and with factors that affect soil saturation (texture, structure, compaction) and NO3− availability (fertilization). Rates of in situ N2O flux were low; however, when recently fertilized soils saturated with water were incubated in the laboratory, we saw extraordinarily high rates of N2O production for the first few hours of incubation, followed by rapid N2O consumption later in the experiment. These findings indicate a lag time between accelerated N2O production and counterbalancing increases in N2O consumption; thus, we cannot yet conclude that lawns are an insignificant source of N2O in our study area.