David, couldn't that be explained by the fact that after the war and well into the 1870s:

1. A vast number of Southern farms were devestated, if not completely destroyed vs. untouched farms in the north

2. Many of the Southern heads of household and their children old enough to farm were dead, injured or missing.

3. Many of the surviving Southern heads of household and their children old enough to farm simply left the South for greener pastures beyond the Mississippi.

4. Many of the Southern plantation slaves moved north in the false hope that they would find greener pastures there.

Does that help explain your data, David?