Are crop yields increasing fast enough to feed 9.6 billion by 2050?

Not according to the PLOS One study Yield Trends Are Insufficient to Double Global Crop Production by 2050 by Deepak K. Ray, Nathaniel D. Mueller, Paul C. West, Jonathan A. Foley. The projected trends are estimated by best-fit linear, non-compounding rates of yield change between 1989 and 2008 for these crops.

Thanks to @MarkLynas for linking the Brad Plumer Washington Post Wonkblog.