The International Journal of Agricultural Sustainability recently dedicated an entire issue to sustainable intensification of agriculture in Africa. This is to say that, despite common narratives of decreasing productivity and environmental degradation in Africa, in many places and sectors of the continent there has been an environmentally-friendly intensification of agriculture over the past few decades. Here is the initial editorial of the issue, giving an overview of agricultural intensification in Africa. All the articles are available free for download for a limited time.
On the same note, here's an offer for a fully-funded PhD position at the Swedish University of Agricultural Sciences, studying African agricultural intensification.