What in the world is sustainable about that?! That's why we've been transitioning to farming practices that do not rely on plowing. Instead, we use heavy mulch cover (which reduces the problematic erosion that is so common with heavy African rainfalls and keeps the moisture in the soil when the hot equatorial sun comes out) and a method called "planting stations." Without going into boring agricultural detail, the benefit of this method is that it increases organic matter and sustains high quality soil. For the those not so savvy on farming and scientific lingo, those are very important factors.
We still like the convenience of our tractor to haul and transport; and if anyone wants to donate a more reliable one, we won't turn it down! :) But as we seek to model farming practices that can be replicated in the community and even improve local farmers' crops and yields, we cannot depend on our undependable tractor quite so much.