How low can you go with soybean populations?

Soybean seeding rates have gotten a lot higher over the years.  I remember 80,000 plants being considered a high population in 30 inch rows.  Many people are now planting double that rate.  I ran across this article from 2012 documenting research on soybean populations.  The researchers concluded that rates of 120,000 are adequate.  Their research seems to support what Marion Calmer shared this winter at the National No-Till Conference.  Calmer said that all his studies showed that he was not justified economically to plant more than 75,000 even though yields were a bit higher at higher rates.  He also says the narrower the rows, the better.  Cutting rates in half may seem radical, but cutting them by 25% seems reasonable.  120,000 to 130,000 should be more than adequate.