Physiological maturity in soybeans is indicated by what characteristic?

Physiological maturity in soybeans is primarily indicated by the fruit turning yellow and the seeds rattling within the pods. At this stage, the beans have reached their maximum dry weight, and the plant has completed its lifecycle. The seeds inside the pods become firm, and their moisture content decreases, which leads to this rattling effect when the pods are shaken. This characteristic serves as a clear signal for growers to determine the optimal time for harvest, as it signifies that the crop is ready for processing or sale.

In contrast, features such as leaves turning red or stems beginning to dry may be associated with the plant's life cycle but do not specifically indicate physiological maturity. Similarly, while flowers dropping off can occur at various stages of development as the plant transitions from flowering to pod and seed development, this does not correlate directly to physiological maturity.