Is organic farming productive enough?

Um, yes. From Chews Wise:

Another report out of the Leopold Center for Sustainable Agriculture at the University of Iowa is also significant, for it demonstrates the long-term yield potential of organic methods.

The now nine-year-old trials "convincingly show greater yield, increased profitability, and steadily improved soil quality in organic over conventional rotations," the Leopold Center stated.

And that's only one of three recent studies that Samuel Fromartz cites in this post. Whole thing definitely worth a read.