Comparing continuous-corn and soybean-corn rotation cropping systems in the U.S. central Midwest: Trade-offs among crop yield, nutrient losses, and change in soil organic carbon

Soybean-corn (S-C) is the most common cropping sequence in the U.S. Midwest, known for improving corn yield compared with continuous corn (C-C). However, the underlying mechanisms and impacts on crop productivity, environmental sustainability, and economic returns are not fully understood. Using the agroecosystem model, ecosys, we simulated S-C and C-C systems under different nitrogen (N) fertilizer application rates, demonstrating good performance in capturing N rate-corn yield responses and CO₂ fluxes across 10 Illinois sites. Our analysis revealed: (1) under normal N rates (151 kg N/ha), soybean residues contributed an average of 36% less carbon but 47% more N than corn, resulting in higher early spring soil temperatures and net mineralization in the subsequent corn year, boosting corn yields for S-C relative to C-C. This yield benefit was reduced with higher N rates. (2) S-C reduced soil organic carbon (SOC) relative to C-C due to faster decomposition of soybean residue under normal N rates, but mitigated nitrous oxide (N₂O) and ammonia (NH₃) emissions. Effects on N leaching varied, with reductions during soybean years and increases in the following corn years. N rates shifted the relative differences of SOC and N losses between S-C and C-C. (3) Economically, S-C provided $1133/ha higher returns than C-C at low N rates (50 kg N/ha) under typical market conditions (soybean: $410/Mg, corn: $178/Mg, and N fertilizer: $193/Mg). However, this advantage diminished at higher N rates due to increased costs and smaller corn yield gains, especially under extreme market scenarios with high corn prices and lower soybean-to-corn and fertilizer-to-corn price ratios. These findings highlight trade-offs among crop yield, nutrient losses and soil carbon change by adopting S-C in the U.S. central Midwestern cropping systems.