Recent Daycent Model Development and Testing for N Gas Volatilization and Nitrate Leaching.

The DayCent ecosystem model is widely used to investigate the impacts of land management practices on net soil (including indirect N₂O) GHG emissions. Submodels for most N cycling processes (plant N uptake, N mineralization resulting from litter and soil organic matter decomposition, nitrification, denitrification, nitrate leaching) are presently included. However, the current release version of the model does not account for ammonia volatilization associated with urea fertilizer amendments. This is an important limitation because unlike N₂O, NH₃ losses are often significant from an N balance perspective (e.g., the IPCC Tier 1 default factors for applied fertilizer N are 1% for N₂O and 10% for NH₃). An ammonia volatilization sub-model was recently developed and implemented into the test version of the model. Results of model evaluations using field observations of NH₃ emissions will be presented. Model testing of other simulated N vectors that contribute to indirect N₂O (NOx emissions, NO₃ leaching) will also be presented.