How did the black codes provide a steady source of labor for whites who owned farms?

Forced sharecropping or tenant farming--the black codes created discrimination against blacks preventing them from other jobs or owning land.

The black codes were laws limiting the rights of freedmen and didn't allow for blacks to get land or different jobs. Being land owners still needed labor, free blacks were left with no other option but to continue working the land they had once been enslaved. It led to a system of debt and cycles of poverty which took generations before blacks saw progress.