Here are the rules straight from the 2008/2009 Hunting and Trapping regs:

Prohibited Devices and Activities
You may not use dogs, domestic animals, bait,
radios, handguns, rifles and crossbows (except as
described on p. 23), automobiles, aircraft, electronic
calls or any mechanical conveyance or device to hunt
deer. Paraplegics and single- or double-leg amputees
may hunt from any stationary motor-driven conveyance.
“Paraplegic” means an individual afflicted
with paralysis of the lower half of the body with the
involvement of both legs, usually due to disease or
injury to the spinal cord.
“Bait” means grain, fruit, vegetables, nuts, hay,
salt, mineral blocks, or any other natural food materials,
commercial products containing natural food materials,
or by-products of such materials transported
to or placed in an area for the purpose of attracting
wildlife. Bait does not include food placed during
normal agricultural activities.

Here are the full regs: http://www.iowadnr.gov/law/files/08huntingregs.pdf

I put out one or more mineral blocks, usually in mid July when I set up my game camera and they are always long gone by the time the season starts, so I don't consider that "baiting for the purpose of hunting".