Here is a selection of cotton loading and boat rowing songs (I think), with music, that I haven't come across before now. It's in a piece from 1918, in a larger collection called JAZZ IN PRINT (1856-1929): AN ANTHOLOGY OF SELECTED EARLY READINGS IN JAZZ, by Karl Koenig (2002). The songs seem earlier.

http://books.google.com/books?id=sol334hPuRoC&pg=PA125&dq=cotton+loading+songs&lr=&cd=25#v=onepage&q=cotton%20loading%20songs&f=

It does introduce a genre of songs we haven't really looked at but which are also "call/response" songs, namely religious songs. The author of this article says, "the songs the Negro seems to prefer while working are the religious ones."