I used to have a recording of this by Guy Carawan, on an album called 'A Guy Called Carawan'. To the best of my recollection, it was credited to one of the Lomaxes and the words were along the lines of:

Long summer days make a white man lazy
Long summer days
Those long summer days make a slave run away sir
Long summer days

He ran away to see Miss Mary
He ran away to see his little baby

I'm down in the bottom picking that cotton

The master killed a Jersey Bull, got himself a bellyful

Oh the long summer, long summer, long summer days