Tile spacing impacts on Zea mays L. yield and drainage water nitrate load

The nitrogen (N) load to surface water introduced by subsurface tile drains is a function of soluble N concentration and drainflow volume. A 6-year study characterized the impact of tile spacing on the inter-related factors of monoculture corn yield, N concentration in drainage water, and total drainage water mass N loss for a poorly drained Mollisol. Tile drains were installed at spacings of 10, 20, and 30 m. Yields and grain N were quantified as a function of lateral distance from the tile. Drainflow was monitored continuously with nitrate (NO 3-N) measured in daily, flow proportional aliquots. A 20 m tile spacing (20 m TS) maximized crop yield (7933 kg ha −1) and N accumulation in grain (109 kg ha −1) with slightly lower yields (1 in 4 of 6 years, and results from all treatments suggest that significant dilutions of drainage water concentrations with large or prolonged flushing events does not occur. The magnitude of daily and seasonal flow variations far exceeded that of NO 3-N concentration making discharge the more dominant factor in determining temporal variation in N export.