Fig. 2. Quadratic-plus-plateau response curves for (a) years, (b) quadrants, and (c) irrigation treatments. Optimized total N rates at 98% of maximum yield are indicated by vertical dashed lines. Maximum yields are indicated by large circles. Heavy solid and dashed lines are for all yield observations over the course of the study. The current North Dakota State University recommendation (dashed-dotted line) is based on 21.4 kg of N per Mg of corn grain yield, which is equivalent to 1.2 lb of N per standard (56 lb) bushel of corn.