Effects of tillage practices on phosphorus transport in tile drain effluent under sandy loam agricultural soils in Ontario, Canada

Agricultural watersheds have been identified as a source of nutrients to surface water bodies, contributing to the degradation of water quality. Reduced till (RT) management practices have been employed to reduce the potential for particulate P loss in surface runoff, but may increase the transfer of dissolved reactive phosphorus (DRP) into tile drains. It is unclear if RT increases P losses in tile drainage when nutrient management strategies are used and fertilizers are applied in the subsurface. It is also unclear how these management strategies perform year round, including during the snowmelt period. The objectives of this study are to quantify year round losses of runoff, DRP and total phosphorus (TP) losses from drainage tiles beneath annual disk till (AT) and reduced till (RT) plots, and, to investigate the role of seasonality (particularly winter snowmelt) on runoff and P losses. Results indicate that both runoff and P-export were episodic across all plots and most annual losses occurred during a few key events under heavy precipitation or snowmelt events. Runoff and P losses through drainage tiles were primarily observed between October and May, with most losses occurring in March during snowmelt. Tillage practices did not affect DRP or TP concentrations or loads in tile drainage. This study has highlighted the importance of the non-growing season (particularly winter) in annual P loss, and has demonstrated that the cumulative Best Management Practices (BMPs) used at the study sites may be an effective way to reduce P losses in tile drain effluent.