On a global scale, soybean (Glycine max (L.) Merr.) is cultivated across a wide range of environmental conditions, characterized by variable temperatures and day lengths. It is important to gather information about different maturity group’s phenology and growth patterns to enhance agricultural practices and develop various soybean crop models. We conducted two experiments focusing on soybean maturity groups, commonly used cultivars for early and late maturity groups (one cultivar for each maturity group), one with varying day/night temperatures (22/14, 26/18, 30/22, 34/26, and 40/32°C) under a constant day length of 12.5/11.5 hours. Second, we investigated day lengths of 12.0, 12.5, 13.0, 13.5, 14.0, and 14.5 hours under constant temperature (26°C). We examined various morpho-phenological traits, including plant height, branch number per plant, vegetative development rate, and days to the first flower. Long-day lengths were found to increase the number of branches per plant, whereas shorter-day lengths led to earlier flowering in the cultivars utilized for the experiment. The duration until the first flower was prolonged under lower temperatures and longer day lengths. As a result, understanding the impacts of temperatures and day lengths and their interactions during the leaf, branch, and flowering stages will significantly contribute to improving seed production in future environmental conditions. Furthermore, the insights gained from this study will play an important role in enhancing soybean breeding programs and improving soybean crop models.
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