Optimizing sowing dates to increase maize yield across the Huanghuaihai Plain in China

With the aim of adapting agricultural practices to climate warming, this study projected sowing dates for summer maize in the 2030s (2031–2040) across the Huanghuaihai Plain by analyzing key photo-thermal variables derived from field experiments and projected future climate data under Shared Socioeconomic Pathway 2–4.5 within a restricted planting season. Results showed that growing degree days (GDD) during the active dry matter accumulation period (AP), killing degree days (KDD) during AP, and GDD during the late dry matter accumulation period (LP) explained most yield variation and were used for determining suitable sowing windows. Thresholds of them were 571 ℃ d, 21 ℃ d and 411 ℃ d, respectively. In the 2030s, postponing sowing dates and shifting planting regions northward resulted in gradual declines in KDD during AP and GDD during LP. The proportion of regions limited by KDD and GDD changed from 66% to 0% and from 3% to 100% when sowing dates were postponed from June 1 to July 15. Suitable sowing dates for maize were determined as follows: June 25 to July 10 in regions south of 34°N, June 5 to June 30 between 34°N and 39°N, and before June 20 in regions north of 39°N.