Abstract
The recent climate change, especially the extremely high temperature in summer, is seriously affecting crop yield and quality in Japan. We analyzed the effects of temperature and soil moisture anomalies on soybean phenology, yield, quality, and disorders using yield performance trial data from four representative breeding sites from 2008 to 2024. Analysis based on 17-year means, including the record-hot years 2023 and 2024, clarified the impacts of abnormally hot weather. Days to flowering were shortened by 1.7days per 1°C, and days from flowering to maturity were reduced under lower soil moisture. Yield showed a weak but negative relationship with the temperature increase during the flowering-to-maturity stage, indicating a tendency for reduced yield under higher temperatures. The 100-seed weight decreased with increasing temperature (1.2 g per 1°C), and seed protein content also decreased (0.5% per 1°C); both also tended to decrease under drier conditions. The relationship between the green stem disorder and temperature was unclear, but seed coat cracking and wrinkling showed weak positive relationships with increasing temperature, suggesting that high temperatures tend to promote these disorders. These results indicate that high temperature and drought interacted to reduce yield and quality, with marked impacts in 2023 and 2024. This nationwide analysis demonstrates that serious impacts can occur even in cool regions and provides a basis for stabilizing soybean production under climate change.
