For many fruits, organic farming was nearly as productive as conventional farming (an average difference of just 3%). Cereals and veggies are where organic farming got trashed, with yields averaging 26 and 33% lower than conventional agriculture.
So the data suggests that switching to organic farming for specific crops like various fruits might be a smart move; the slight loss in productivity would be a small price to pay for the environmental benefit. Yet for other crops like corn, wheat and soybeans, organic farming would cut yields substantially. You could argue we grow more corn than we need, of course, because a lot of our corn goes to ethanol (thanks, Congress) and cattle (which is a crazy-inefficient use of corn, BTW — the ratio of corn consumed to beef produced is terrible). But the fact remains that organic farming is not the universal solution its advocates claim it to be. It looks like a good solution for a variety of specific crops, but we probably can’t do all our farming organically, because for many other crops it just doesn’t have anywhere near equivalent productivity.