Simulations of carbon and nitrogen dynamics in turfgrass systems using the DAYCENT model
Date
2012
Authors
Zhang, Yao, author
Qian, Yaling, advisor
Parton, William J., committee member
Koski, Anthony J., committee member
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Abstract
Ecosystem modeling offers an opportunity to better understand the carbon and nitrogen dynamics in a certain ecosystem. Modeling provides a way for researchers to expand their research to larger scales or other situations where field measurements are difficult or costly to conduct. In this study, the DAYCENT ecosystem model was parameterized and validated under home lawn conditions. Long-term effects of irrigation and fertilization on turfgrass quality, soil carbon and nitrogen sequestration, and nitrous oxide (N2O) emissions were investigated. The DAYCENT model was also used as a tool to develop best management practices (BMPs) for a Kentucky bluegrass lawn. Clipping yields, evapotranspiration (ET), deep percolation, nitrate leaching, and soil temperature of a Kentucky bluegrass lawn were simulated and compared with the measured values from a three-year lysimeter study. Parameters that control damping factors of soil temperature and nitrate leaching rate were modified to reflect the unique properties of turfgrass ecosystems. The prediction of weekly ET and deep percolation of the three years was acceptable (r > 0.6). The simulated clipping yield was improved compared to the monthly time step CENTURY ecosystem model, with the r value increased from -0.32 to 0.74. Modeled N2O emissions were validated for Kentucky bluegrass (Poa pratensis L.) and perennial ryegrass (Lolium perenne L.). The annual cumulative N2O emissions predicted by the DAYCENT model were close to the measured emission rates of Kentucky bluegrass sites in Colorado (within 16% of the observed values). For the perennial ryegrass site in Kansas, the DAYCENT model overestimated the N2O emissions for all treatments by about 200% (urea and ammonium sulfate at high rate and urea at low rate). After including the effect of biological nitrification inhibition (BNI) in the root exudate, the DAYCENT model properly simulated the N2O emissions for all treatments (within 8% of the observed values). After calibration and validation, the DAYCENT model was further used to predict best management practices (best irrigation and nitrogen fertilization rates) for a Kentucky bluegrass lawn. Irrigation that decreases from 100% potential evapotranspiration (PET) to 60% PET is predicted to reduce 50-percent of annual net production in the semi-arid region. The model simulation suggested that gradually reducing fertilization as the lawn ages from 0 to 50 years would significantly reduce long-term nitrate leaching and N2O emissions when compared to applying nitrogen at a constant rate (at 150 kg N ha-1 yr-1). Our simulation indicates that a Kentucky bluegrass lawn could change from a sink to a weak source of greenhouse gas (GHG) emissions about 20 to 30 years after establishment.
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Subject
DayCent
turfgrass
nitrous oxide
modeling
GWP