See slides 25-32 of Potash Corp's latest Q1 2014 Market Analysis Report slide show here

http://www.potashcorp.com/slideshow

Africa accounts for 15 percent of the world’s population and is one of the regions projected to experience significant population growth in the coming decades. Primarily driven by Sub-Saharan Africa, population on this continent is projected to grow by 35 million every year – approximately the current population of Canada.
At the same time, a big shift to urbanization is expected. The urban population share is projected to surpass 60 percent compared to the current 40 percent. Two factors are influencing this urban migration: economic growth that will drive employment opportunities in urban markets, and government initiatives to encourage consolidation among primary agriculture producers in an effort to increase food production. This is an important shift, as urban consumers tend to eat more food and have more balanced diets. -

See more at: http://www.potashcorp.com/slideshow/384/#sthash.R5SLFedW.dpuf