Topographically heterogeneous agricultural landscapes can complicate and accelerate agrochemical contamination of streams due to rapid transport of water and chemicals to poorly drained lower-landscape positions and shallow ground water. In the semiarid Palouse region, large parts of these landscapes have been tile drained to enhance crop yield. From 2000-2004 we monitored the discharge of a tile drain (TD) and a nearby profile of soil water for nitrate concentration ([NO(3)]), electrical conductivity level (EC), and water content to develop a conceptual framework describing soil nitrate occurrence and loss via subsurface pathways. Tile-drain baseflow [NO(3)] was consistently 4 mg N L(-1) and baseflow EC was 200 to 300 microS cm(-1). Each year sudden synoptic increases in TD discharge and [NO(3)] occurred in early winter following approximately 150 mm of fall precipitation, which saturated the soil and mobilized high-[NO(3)] soil water throughout the profile. The greatest TD [NO(3)] (20-30 mg N L(-1)) occurred approximately contemporaneous with greatest TD discharges. The EC decrease each year (to approximately 100 microS cm(-1)) during high discharge, a dilution effect, lagged approximately 1 mo behind the first appearance of high [NO(3)] and was consistent with advective transport of low-EC water from the shallow profile under saturated conditions. Water-budget considerations and temporal [NO(3)] patterns suggest that these processes deliver water to the TD from both lower- and upper-slope positions, the latter via lateral flow during the high-flow season. Management practices that reduce the fall reservoir of soil nitrate might be effective in reducing N loading to streams and shallow ground water in this region.