Tillage practices can affect the formation and persistence of preferential flow paths and their role in transporting portion of the surface applied chemicals to groundwater. Field experiments were conducted to quantify tillage (chisel, moldboard, ridge and no-till) effects on subsurface drain flow and losses of nitrate-nitrogen (NO3-N), atrazine, and alachlor to shallow groundwater. Rapid increase in subsurface drain flow rates following heavy rains indicate the preferential movements of rain water to subsurface tile drains. The sudden decreases in NO3-N concentrations and increase in the concentrations of atrazine, and alachlor in subsurface drain water, particularly under no-till and ridge till systems, supports the role of preferential flow paths to carry contaminants to shallow water table depth and its overall effects on groundwater quality.