After the Civil War, there were obviously no more plantations staffed by slaves and so the agricultural economy had to be reorganized in some way. The two main new forms that arose were sharecropping and the crop-lien system. Both of these were ways that allowed farmers with small landholdings or without any land at all to raise crops. Both also allowed large landowners or merchants to abuse and control the small farmers.
Sharecropping was a system in which a landlord made a deal with a farmer. The farmer would work a certain area of the landlord's land and would, in exchange, give the landlord a certain percent of the crop. Often, the landlord would also provide things like seeds and tools for an added percentage of the crop. The crop-lien system was used in a similar way. The farmer would borrow from a merchant to buy necessities like seeds and food. The merchant would take a lien on the farmer's crop in return.
In both cases, the landlord or merchant had the upper hand. The farmer needed the resources provided and would have to pay whatever sort of interest and whatever prices were charged. Once a farmer became indebted to a particular merchant, the merchant essentially owned the farmer legally because the farmer would have to continue to borrow from that merchant in hopes of paying off the prior debt.
In these ways, the rich landowners and merchants of the South were able to keep agriculture alive and to remain in control of the economic system after the end of slavery.