No experience in the area, but I watched the documentary on the UN project and there is a whole system to it: first the semi circular round bowls, planted with sorghum or some sort of hearty-food producing plant, then rows of crops with a ditch behind that, and trees planted on either side (or in front of it?). Anyway, the soil does erode but by then the landscape is pretty set and needs little maintenance. The great green wall is an amazing project for humanity.