Sensitivity of the economically optimum N rate (EONR) to (a and b) attainable yield, Ya, and (c and d) soil organic C, SOC, as simulated by Maize-N. Two baseline cases are shown: (a and c) an eastern South Dakota site (Brookings, SD) with Ya of 10.8 Mg ha−1, 2.42% SOC, a previous crop of soybean (soy), and no-till management (nt), and (b and d) a central Nebraska site (Clay Center, NE) with Ya of 11.6 Mg ha−1, 1.75% SOC, a previous crop of maize, and conventional tillage (ct). Sensitivity tests included counterpart options for soil management (no-till vs. conventional tillage) and the previous crop (maize vs. soybean) at each site, as shown by the different symbols. Vertical and horizontal dotted lines indicate baseline values for SOC and simulated EONR, respectively. For reference purpose, the values of Ya and SOC associated with the various percentages of Ya and SOC are shown near the horizontal axis at the top and bottom of each panel. Similarly, the percentage increase or decrease in EONR above or below the baseline is shown on the right side of each panel.