Here is a picture of early planted soybeans last Monday. Leaves are turning yellow and brown and falling off. The beans in the pods are at full maturity. Below is a photo of the same field taken yesterday.
Seminole Ag Agent Rome Ethredge posted about irrigation termination on Seminole Crop E-News saying, You are generally safe to terminate irrigation if you have good soil moisture when the seeds fill the pods and the pods start to change to the yellow color in the top 4 nodes of the plant. Mississippi State also has a good blog post concerning Soybean Irrigation Termination that goes into growth stage specifics.