From this lecture by John Reganold of WSU at Iowa State in 2009, drawing from hundreds of studies.
"The bottom line from this is that organic farming produces adequate yields of high quality. I don't like it when people say 'Well, organic agriculture can't feed the world.' Guess what: Conventional farming can't feed the world, no-till farming can't feed the world. If I had to pick a system that might be able to feed the world, it might be integrated... People automatically jump from 'Well, you can't feed the world, we'll dismiss that.' You can't do that. Organic agriculture can be a player."
"When we do these kinds of studies--organic, no-till, conventional, whatever--we don't take into account externalities. Oh, you're losing soil. Did you put that into the equation? Someone losing soil, that should be a negative dollar amount. That's an ecosystem service that we don't want to lose. What about if you have phosphorous runoff with erosion? It gets into the rivers, the lakes. Do we account for that? Do we accountt for nitrate leaching? If you take those into account, because the environmental benefits of organic are usually better, it would benefit the organic even more. I haven't seen a study that has done that."
"I was at this wine growers retreat, all the guys were into biodynamic... I remember the last person that spoke got up there, and this is how he started his talk: 'How many out there have a 401k plan for their workers? Raise your hand.' Nobody raised their hand... He said, 'That's what I thought. You do that and you're sustainable.' I was blown away, these people were talking about environmental sustainability, but they're paying their workers crap."