I have come to the belief that organic or natural farming is about 75-80% as efficient as chemical farming as practiced today.  Which would mean we would need to increase the farm land another 25% to keep up with output.    

BUT, organic farming is much more cost effective and leaves the fields healthy, while chemical farming sterilizes the fields requiring continued chemical supplementation, greater mechanical intrusion and adapted crops annually.  The risk of collapse is real and a new dust bowl if the farming ever gets reduced.