Maximum net economic return to N (MRTN indicated by solid symbols) and profitable N rate range (indicated by open symbols) for corn following soybean (121 SC sites) and corn following corn (56 CC sites) in Iowa at different N:corn price ratios. Net return is the value of corn grain produced minus the N fertilization cost. Corn grain price held constant at $2.20/bu, and N prices varied at $0.11, $0.22, $0.33, and $0.44/lb N to give price ratios of 0.05, 0.10, 0.15, and 0.20, respectively.