Evaluation of a Microbial Denitrification Model in the Environmental Policy Integrated Climate Model.

Nitrous oxide (N₂O) is a potent greenhouse gas for which agriculture is the dominant source of global anthropogenic emissions. Agricultural N₂O emissions are strongly influenced by nitrogen management practices such as the timing, rate, type, and placement of nitrogen fertilizer applications as well as tillage, irrigation, drainage, and crop rotation. Due to the complexity of these systems, models can be useful tools for understanding and predicting site-specific responses to different management practices, as well as scaling up production to quantify emissions impacts at regional, national, or global scales. To this end, a new denitrification model was recently added to the Environmental Policy Integrated Climate (EPIC) model. The added model takes advantage of existing soil water and soil carbon and nitrogen cycling routines in EPIC to implement a microbial based denitrification model. The model was evaluated using data from the main cropping system experiment at the Kellogg Biological Station Long Term Ecological Research Site (42°24’ N, 85°24’ W) in southwestern Michigan. The experiment used for model evaluation has been under a conventionally managed no-till corn (Zea mays)-soybean (Glycine max)-winter wheat (Triticum aestivum) rotation since the experiment was established in 1989. The model was evaluated against field measured N₂O surface fluxes, soil moisture dynamics, soil nitrogen dynamics, soil carbon dynamics, and crop yield, providing a long-term and holistic evaluation of a model for a complex and interactive system.