Analysis and Field‐Evaluation of the CERES Models' Soil Components: Nitrogen Transfer and Transformations

For estimating N losses in soil‐crop systems with the simple and functional CERES models, we evaluated their N modules and compared them with the more complex SLIM (for solute transport) and NCSOIL (for N mineralization) models. SLIM is based on the concept of immobile and mobile water regions in soil, and CERES on a piston‐flow hypothesis. In NCSOIL, the soil organic matter (SOM) mineralizes through two active pools, whereas in CERES the SOM decomposes as a whole with a gross decay rate. We used data on mineral N dynamics under bare soils (silt loam, loam, and sandy loam) from 1‐yr‐long experiments at three locations in France, including measurements of weekly NO 3 leaching fluxes. The original CERES mineralization submodel did not correctly simulate N supply from potentially degradable SOM. When using NCSOIL instead, the simulations improved and CERES predicted NO 3 leaching reasonably well, with a root mean square error of 6 to 21 kg N ha ‐1 , representing 5% of the yearly flux. The SLIM model performed as well, and better simulated the intense NO 3 percolation regime that occurred in wintertime. Its immobile water fraction parameter had to be calibrated, however, or the yearly leaching flux was underestimated. When linked to NCSOIL, the CERES model showed a good potential for estimating N dynamics in soil, even if its piston‐flow type of NO 3 transfer was not always relevant. In such case, SLIM was a more appropriate approach, although it required a site‐specific calibration.