Water table management impacts on phosphorus loads in tile drainage

Increased phosphorus (P) concentrations, consistently exceeding Quebecʹs surface water quality standard of 0.03 mg L−1 total P, caused increased P loads in tile drainage from controlled drainage/subirrigation (CD/SI) plots compared to free drainage (FD) plots in a field study carried out in 2005 in Coteau-du-Lac (southwestern Quebec, Canada). This happened even though the total outflow volumes from CD/SI plots were reduced by 27% compared to FD plots. Of the total P concentration, around 96% was in the form of dissolved P under both treatments. The results also showed that CD/SI had no effect on the soil P concentration and P saturation.