Impacts of Future Climate Change on Comparative Advantages in Yield, Irrigation Water Productivity, and Economic Returns of Summer Soybean and Maize Under Sowing Date Optimization in the Huaibei Plain, China

In China’s Huaibei Plain, summer soybean and maize compete for land due to highly overlapping growing seasons. This study employs the DSSAT model under full irrigation to assess crop climatic adaptability and sowing date optimization across a baseline (2001–2020) and two future emission scenarios (SSP2-4.5 and SSP5-8.5, 2031–2050) under 13 sowing-date treatments, with 10 June as the conventional sowing date for both crops. Results indicate that future summer growing seasons will become warmer and wetter overall. Relative to the baseline, conventional sowing under future climates leads to shortened growth periods and synchronous yield declines, with maize suffering substantially larger yield losses than soybean. Sowing date optimization effectively mitigates these climate-induced yield losses, with recommended adjustments of advancing soybean by 10–15 days and delaying maize by 20 days. Following optimization, maize yield surpasses the baseline by 8.2% under SSP2-4.5 and recovers to near-baseline levels under SSP5-8.5, while soybean yield remains comparable to the baseline under SSP2-4.5 and slightly below it under SSP5-8.5. Maize maintains clear advantages in grain yield and net return, whereas soybean has higher irrigation water economic efficiency, defined as the irrigated–rainfed net return difference per unit irrigation water. Under these simulated full-irrigation conditions, we suggest maintaining a maize-dominant pattern with moderate soybean allocation and optimized sowing dates for both crops as a scenario-based reference for enhancing regional climate adaptability.