I don't know about law in Africa, but Sicily was another grain-producing region of note, and there Rome really didn't institute new local laws. In Sicily Rome basically just took over local laws (Cicero's speeches against Verres indicate this). For example, Rome kept the so-called Lex Hieronica, established by Hiero II of Syracuse, for their administration of Sicily.

Rome did pass laws ordering three million modii of wheat to be paid in tithe, and would purchase additional grain at a price fixed by law (as in the Terentian-Cassian grain law of 73 BC).