Associate Professor Nathan Slaton of the University of Arkansas tells the  AAPFCO  (American Association of Plant Food Control Officials) that efficiency ratio products that they field tested, are fine and as effective as zinc sulfate as long as they are used on a 1 to 1 ratio of what the soil test recommends.  He is firmly against efficiency ratio claims and states that yields are reduced when products are applied based on an efficiency ratio.

For the entire memo click here.