C Sequestration and N2O Emissions in Urban Soils.

Turfgrass is a major vegetation type in the urban and suburban environment.  During the past several years, research has been conducted: 1) to determine carbon sequestration and trace gases fluxes (N₂O, CH₄, and CO₂) in turfgrass systems, 2) to use the calibrated DAYCENT model as a management support system to identify agronomic practices that will reduce carbon footprint.  Carbon sequestrations were accessed using historic soil testing data.   Our results indicated that a rapid soil organic carbon accumulation occurred during the first 0-25 years after turfgrass establishment, at average rates approaching 0.9 and 1.0-ton C ha^-1 yr^-1.  A modified vented chamber method was used to measure turf-soil-atmospheric trace gas exchange.  Several years’ onsite measurements indicated that N₂O emissions varied with variables such as fertilizer rate and type, fertilization time, soil drainage effectiveness, and turfgrass management practices.  Cumulative emissions from fairway under different fertilizer treatments corresponded to 1.2 to 4.7% annual fertilizer N loss. Annual cumulative emissions on the rough corresponded to a 0.6 -1.3% loss of total N applied.  The DAYCENT model simulation suggested that gradually reducing fertilization as the lawn ages from 0 to 50 years would significantly reduce long-term N₂O emissions by approximately 40% when compared to applying N at a constant rate.  Our simulation indicates that a Kentucky bluegrass lawn could change from a sink to a weak source of GHG emissions about 20 to 30 years after establishment.