Impacts of Climate Change on Late Soybean Cultivation in Subtropical Southern Brazil

Soybeans are the most widely produced oilseed and the fifth most cultivated crop in the world. However, their growth and yield are significantly influenced by weather conditions. In Southern Brazil's subtropical climate, farmers employ a double-cropping system, planting corn from late winter to early summer, followed by soybeans, which are sown after the corn harvest-typically in January-and harvested in autumn. This study argues that climate change has benefited late-sown soybeans in Rio Grande do Sul and will continue improving their growing conditions. The aim is to identify climate change's past and future impacts on late-sowing soybean crop yields in this region. We evaluated the effects of climate on soybean yields using the HadGEM2-CC model (CMIP-5) for two scenarios (RCPs 4.5 and 8.5) and for two time periods (mid-and late-century). Additionally, the CSM-CERES-Maize model within DSSAT was also used to simulate corn yields under these climatic conditions. Our climatic analysis indicates an increase in rainfall and temperature, particularly in minimum temperatures, alongside significant rises in both minimum and maximum temperature extremes, and a reduction in frost days. Furthermore, higher atmospheric CO2 levels are projected to enhance net photosynthesis, likely leading to increases in potential yield (Py) with rising CO2 concentrations. Notably, the largest increases in achievable yield (Ay) are anticipated for early sowing dates under the mid- and late-century scenarios of RCP 4.5. Past climate changes have already improved the growth and yield potential of late-sown soybeans in Southern Brazil, a trend expected to continue as climate change further optimizes temperature and rainfall conditions. In conclusion, the late growing season for soybeans is predicted to be extended.