Since I tried to comment on Nature but their comment section was messed up I'll comment here - it appears that they looked at conventional organic farms - that is to say - farms that use similar methods to non-organic farms (monoculture) as opposed to permaculture designed (polyculture) farms. As for the wheat yields being lower - no big surprises there. Modern wheat is a delicate crop that has been engineered to be unhealthy but it's never been easy to grow. We need to change the worlds diet not continue to assume that our western (high-wheat) diet can solve hunger problems. We should switch to nuts and legumes and minimize wheat and grains.