I know biofuels are terrible and will starve us, but check out this Newsweek article on Jatropha. When I was in the Peace Corps in Guinee-Bissau, we used this to grow living fences to keep the goats out of our gardens. It’s the growingest plant I’ve ever seen — whack off a branch from your neighbor’s hedge with a machete, stick it in the ground, and presto, it sprouts like a weed, no irrigation needed.
And — best part — the goddamn goats wouldn’t eat it. It is impossible to properly appreciate the significance of this until you try to start an orange grove in an African village.
Traveling north to the bitter edge of the Sahel, you’d see whole villages circled with it, in a futile attempt to hold back the encroaching Sahara.
It has medicinal purposes, too — if I remember right, women used it for birth control. Note: You might want to double-check that before trying.
I have no idea what the economics are, but where I lived everyone was looking for a secondary cash crop. If the money is right, I see no reason why Jatropha couldn’t and wouldn’t be grown on the margins to keep the family in dried fish and kola nuts.