The problem with subtropical African crops is that it they use different crops from what most people on the Northern Hemisphere grow. The climate and soil conditions are quite different.I've seen a lot of new tech like drone equipment for farming and improved GMO crops. Export this tech. Teach African people how to use them. You will be able to feed both Africa and yourself.
It will take a lot of time and effort developing new crops for subtropical Africa. I think until people in that climate band work on this themselves it won't happen.