Probably not a lot: the subsequent share-cropper contracts were a less effective arrangement than if the blacks had owned their lands themselves and had the planters had to "get competitive" from the get-go. They still ended up relying overwhelmingly on cotton.
While I am unsure re: the situation re: rice, by the 1860 the market -- both nationwide and int'l -- for tobacco/tobacco products had been in a glut for nearly twenty years. Most slave owners in the central southern states, VA, etc, in fact made ends meet by selling "excess" slaves, tobacco being, as it were, sort money losing side-line to add a veneer of respectability.
However, unlike tobacco there was a huge, seemingly never-ending, ever increasing demand -- both nationwide and on int'l markets -- for cotton, esp. American cotton. New York, Philadelphia, Atlanta, etc. would loan the southern farmer money on the condition that he plant cotton -- for they knew there was a eager market for that product. So, more and more, the southern farmer (of any size but the very smallest) stopped a (healthy) diversity of crops and came to plant cotton...nothing but cotton. B/c that's where the money was, and b/c that is the one crop bankers would loan him money on and for.
It wasn't called "King Cotton" for no reason.
(Given the day and age and financial situtation, it's hard to believe that even with 40-acres-and-a-mule that the freed slave would, on average, have achieved much more than a subsistance level.)