Ok I think I might be able to help answer this for you, or at least give you some helpful links to articles/ethnographies on the region!

First, southern Africa is a big area with a wide range of environmental conditions that can effect how pre-colonial societies would have farmed or even if they would have bothered with farming. This map of the rainfall for the region should show that pretty clearly. Also, there are a lot of people in the region who have historically not grown crops, hunters/gatherers and pastoralists mainly, so there's that.

Is their a specific region of Southern Africa you are looking into?