Improving model capability in simulating spatiotemporal variations and flow contributions of nitrate export in tile-drained catchments

•We developed a fully distributed water quality model for tile-drained catchments.•In-field management and catchment features control daily flows of water and NO3-N.•Subsurface flows, especially tile flow, dominate the water and NO3-N loads.•Roles of the model improvements in enhancing prediction accuracy were quantified.