The answer is: They were often still in debt at the end of each harvest.
In sharecropping system, a land owners would give the opportunity for other people to work on their land and get small percentage of profit from the crops that they produced.
At that time, many african americans did not possess the tools that were necessary for taking care of their crops. So landowners rent the tools for them.
The problem is, the amount of the rent for the tools often more than the profit that the african american sharecropper gets from their share. This made them often still in debt at the end of each harvest.