Simulation of nitrous oxide emissions and estimation of global warming potential in turfgrass systems using the daycent model

Nitrous oxide (N₂O) emissions are an important component of the greenhouse gas budget for turfgrasses. To estimate N2O emissions and global warming potential, the DAYCENT ecosystem model was parameterized and applied to turfgrass ecosystems. The annual cumulative N₂O emissions predicted by the DAYCENT model were close to the measured emissionrates of Kentucky bluegrass (Poa pratensis L.) sites in Colorado (within 16% of the observed values). For the perennial ryegrass (Lolium perenne L.) site in Kansas, the DAYCENT model initially overestimated the N₂O emissions forall treatments (urea and ammonium sulfate at 250 kg N ha^-1 yr^-1 and urea at 50 kg N ha^-1yr^-1) by about 200%. After including the effect of biological nitrification inhibition in the root exudateof perennial ryegrass, the DAYCENT model correctly simulated the N₂O emissions for all treatments (within 8% of the observed values). After calibration and validation, the DAYCENT model was used to simulate N₂O emissions and carbon sequestration of a Kentucky bluegrass lawn under a series of management regimes. The model simulation suggested that gradually reducing fertilization as the lawn ages from 0 to 50 yr would significantly reduce long-term N2O emissions by approximately 40% when compared with applying N at a constant rate of 150 kg N ha^-1 yr^-1. Our simulation indicates that a Kentucky bluegrass lawn in Colorado could change from a sink to a weak source of greenhouse gas emissions 20 to 30 yr after establishment.