Development of the DNDC model to improve soil hydrology and incorporate mechanistic tile drainage: A comparative analysis with RZWQM2

The Denitrification Decomposition model (DNDC) has known limitations for simulating soil hydrology which can strongly influence biogeochemical processes. For this study, DNDC's soil hydrological framework was enhanced by including a new sub-model for mechanistic tile drainage, improved water flux, root growth dynamics, and a deeper and heterogeneous soil profile. Comparisons were then conducted against the Root Zone Water Quality Model (RZWQM2), using measurements of soil water storage, runoff, and drainage in eastern Canada and the US Midwest. Simulation of soil water storage (DNDC 0.81 ≤ d ≤ 0.90; RZWQM2 0.76 ≤ d ≤ 0.84), daily water flow (DNDC 0.76 ≤ d ≤ 0.88; RZWQM2 0.77 ≤ d ≤ 0.90) and nitrogen loading to tile drains were improved post-development. DNDC was able to capture the observed differences in water and N losses between conventional drainage and controlled drainage management with sub-irrigation. The enhancements to DNDC's hydrological framework should enable the development of improved biogeochemical processes.