Your average American farmer has hundreds of thousands to millions of dollars in capital equipment, spends a sizable portion of output revenue on inputs (fertilizers, pest control, seeds, insurance, etc.) and is supported by university extension programs, government subsidies and minimum price supports, and on and on and on. The lack of industry to produce inputs and equipment comparable to what is available here will take decades to even close.

Sure you could get _an_ African farmer to American level yields, but that's different than what essentially is economic reorganization for the _majority_ of workers in African economies.

Also, remember this isn't an agile software project that can go through an iteration a day. You plant once a year, you harvest once a year; an entire continent doubling yields in only 15 iterations is pretty good.