The effects of subsurface drainage depth and intensity on nitrate loads in the northern Cornbelt

Keywords: Gulf Hypoxia, Nitrate-nitrogen, Subsurface drainage design, Tile drainage Nitrate loads to surface waters from croplands in the Mississippi River basin are considered a leading cause of hypoxia in the Gulf of Mexico. Subsurface (tile) drainage systems exacerbate nitrate loads to surface waters by providing a pathway for the transport of soluble compounds from the crop rooting zone. This work investigated the role of subsurface drainage depth and drainage intensity (theoretical drainage rate) on nitrate loads to subsurface drains through field experimentation over a five-year period (2001-2005). Subsurface drainage plots were installed on nine subfield-sized plots ranging in size from 0.8 to 2.5 ha. The nine plots comprised two drainage depths (90 and 120 cm) and two drainage intensities: a conventional" intensity of 13 mm d-1 design drainage rate and a "high" intensity of 51 mm d-1