Towards improving the DNDC model for simulating soil hydrology and tile drainage


Smith, W., Z. Qi, B. Grant, W. He, A. VanderZaag, C. Drury, C. Tan, M. and Helmers. Towards improving the DNDC model for simulating soil hydrology and tile drainage. 2019 ASABE Annual International Meet, Boston, Massachusetts, July 7–10, 2019. DOI:


The Denitrification Decomposition (DNDC) model is a widely used process-based model for simulating greenhouse gas emissions and soil carbon change. The model, however, has known limitations for simulating soil hydrology, which is a crucial driver influencing biogeochemical processes. The purpose of this study was to improve DNDC for simulating hydrology, including a new sub-model for mechanistic tile drainage, and then to compare its performance to the Root Zone Water Quality model (RZWQM2) using datasets of runoff and drainage in eastern Canada and the US Midwest. In DNDC, we incorporated a heterogeneous soil profile, extended the soil depth from 50 to 200 cm, and included root penetration and density functions to improve water and N uptake by plants. A fluctuating water table and mechanistic tile drainage were incorporated, including the ability to simulate sub-irrigation and controlled drainage. In order to keep model input and calibration requirements manageable, a cascade water flow approach was maintained, however, a mechanism was included to slow drainage above field capacity. Results indicated that the performance of DNDC for simulating soil water storage and water and N flow to tile drains were greatly improved, with the performance being at least equal to RZWQM2. After the developments, the DNDC model was able to capture the differences in water and N losses that occurred between conventional drainage and controlled drainage management with sub-irrigation. The model improvements should increase the performance of DNDC for simulating biogeochemical processes and for assessing drainage design implications on water quality and GHG emissions.