The Effect of Water Table Management on the Migration of Phosphorus and on Grain Corn in Southwestern Quebec

摘要

In southwestern Quebec (Canada), annual precipitation generally exceeds evapotranspiration by 300 to 700 mm. Subsurface drainage is commonly used to improve the poor natural drainage capacity of the region's agricultural fields, characterized by a flat topography and by the fact that they are underlain by clay. Lowering the water table with artificial drainage has been shown to improve crop growth. However, high pesticide and nutrient losses have sometimes been attributed to subsurface drainage. Water table management (WTM) allows the maintenance of a constant water table depth in a field, by controlling drainage outflows and by providing additional water by subirrigation when crops need it. Water table management generally increases yields comparedwith conventional free drainage. This study aimed at assessing the effect of WTM on phosphorus (P) losses via tile drainage. Two drainage treatments were studied between May 2001 and October 2002, in a grain corn field located in southwestern Quebec: conventional free drainage, and WTM, with a design water table depth of 0.6 m below the ground level. Drainflow was recorded and water samples were automatically collected from tile drains. The samples were analysed for dissolved inorganic P (DIP) and total dissolved P (DP). During growing seasons, P concentrations in drainage water were more than twice as high in plots under WTM than in plots under conventional free drainage. Significant increases in drainage outflow volumes (more than 45%), loads (morethan 250%), and grain corn yields (35%) were also observed under WTM.