Abstract
<jats:p>Reactive nitrogen (Nr) gases (NH3, N2O, and NOx) emitted from agricultural fields constitute a substantial portion of the reactive nitrogen gases from land to the atmosphere. Here, we develop a new model, the Flows of Agricultural Nitrogen (FANv3), coupled with a modified version of the Community Climate Model (CLM5.1) to produce a model (CLM-FANv3) that couples the NH3 emissions as simulated by FANv3 with the NOx and N2O emissions simulated in the CLM5.1. CLM-FANv3 is developed under the strong observational constraints of measurements conducted in mesocosms from a US Corn-Belt agricultural site where corn is planted subject to different fertilizer amounts and soil types. Combining measurements and models allows us to integrate disparate measurements of the mesocosm into more complete insights into the dynamic flow of nitrogen within the soil system. The new nitrogen dynamics in CLM-FANv3, as constrained by the measurements, are significantly different than CLM5.1 with much-enhanced nitrification (~2.5x CLM5.1), enhanced uptake of nitrate in plants (~5x CLM5.1), increased nitrate leaching (an order of magnitude larger than CLM5.1) and decreased denitrification (about half of CLM5.1) at the mesocosm site. NH3 emissions are comparable to denitrification to N2, a significant term neglected in most Earth System Models. The emissions of NOx and N2O are in reasonable agreement with the measurements and are improved over CLM5.1. The strong measurement constraints have important implications for simulating expected future changes in Nr emissions. Differences in nitrogen cycling also impact projected amounts of carbon stored in agricultural soils over the long term.</jats:p>