I can't give you an objective basis for my comment that I've heard that
differences within soil types can be as great as differences between soil
types. I'm basing my comments on anecdotal observations from several
people I know who work with farmers doing yield monitoring. If you need
specific sources, I can and will be happy to share those in email to
you.
Jim - Farmer - Iowa City, IA,
jnmeade@blue.weeg.uiowa.edu