The Federal Reserve Bank of Kansas City publishes several good Ag related articles each year. They recently did a quick snapshot of the US Ag Economy and one of the slides represented the current corn production for the world.
Current world production for 2009 was slightly greater than about 27 billion bushels. If each country could adopt our corn technology, it is projected that corn production would be about 50 billion bushels.
Sub-Saharan Africa could go from about 2 billion bushels of production to over 12 billion bushels alone.
Therefore, even though the world's population will continue to grow, it should be able to handle the growth for many years by just taking advantage of the technology that we have now.