We have a field that can yield 40 bu on soybeans without any meaningful rain (less than 3/4" 1 or 2 tenths at a time) from emerges to maturity.  We were in D4 at beginning of oct that year.  It could have rained 3" in Sept and we would have still been in a drought maybe they would have made 60 then. 

I thought that everyone knows that soils and weather are generally better for raising soybeans in Iowa than they are in southern Kansas.