Subsurface nutrient export from a cropped field to an agricultural stream: Implications for targeting edge-of-field practices

•Tiles and groundwater from a cropped field contribute nutrients to an Iowa stream.•Nitrogen and phosphorus loads are dominated by tile discharge (>96 %).•The annual proportion of tile discharge to streams decreases with watershed area.•Edge-of-field practices are needed to reduce subsurface delivery of nitrate to streams.