It is obvious that bees from a colony placed in the middle of a on a 160 acre field of blooming clover will forage much closer to the hive if than if they are stuck in the middle of a NY forest.  If we knew that 95% of foragers on a blooming hay half or quarter section (the Canadian prairie term for 320 and 160 acre divisions) fields did not stray outside the area, I would feel confident in supporting this guideline as a component of organic beekeeping.  Of course the remaining 5% could be foraging on a heavily managed canola field, but is this same small risk not part and parcel of any organic field crop when a neighbor's synthetic pesticide occasionally drifts?  As Jerry and Peter pointed out, you can never completely eliminate bees from foraging across a vast distance, but I want to know can you restrict the majority of foraging area to a limited area... specifically in our region a 160 - 320 acre organic hay field.

I don't think there are studies that have tested the situation I am interested in, although Jerry would know and I would like his comments.  How are the current estimates of honey bee foraging distances are derived?  By looking through what literature I have on the subject I found the following:

Although honey bees have been found to forage over distances up to 10 km from their colony (reviewed in Winston 1987), bees will only forage such large distances when no other competing food sources are available.  Honey bees located in a temperate forest most commonly foraged within 600 to 800m of their colony and 95% of the foraging activity was restricted to within 6km of the hive (Seely 1985).  In another foraging study in a temperate forest only a small fraction of foragers (2%) were observed to recruit nestmates to floral sources beyond 4km (Visscher and Seely 1982 quoted from Seely 1985).  Forests, however, tend to have less concentrated nectar sources than agricultural settings, where the median foraging radius has been observed to be within a few hundred meters of the hive (reviewed in Visscher and Seely 1982).

Evidence suggests that nectar foragers assess the profitability of their food source and tend to avoid distant flower patches when closer patches are present, as distant patches require more energy to fly to.  Experiments have shown that bees will preferentially recruit nestmates to a food source 50m away over 1250m away even if the distant source has nectar that is 30% more concentrated in sugar (Seely et al. 1991).  Foragers would prefer to recruit to the more distant source only when the reward was 3.5 times the sugar concentration of the closer nectar source.

References:
Seely, T. D.  1985.  Honeybee Ecology.  Princeton University Press.  Princeton, NJ.

Seely, T. D., S. Camazine and J. Sneyd.  1991.  Collective decision-making in honey bee colonies: how colonies choose among nectar sources.  Behavioral Ecology and Sociobiology.  28: 277-290.

Visscher, P. K. and T. D. Seely.  1982.  Foraging strategy of honeybee
colonies in a temperate deciduous forest.  Ecology.  63: 1790-1801.

Winston, M. L.  1987.  The Biology of the Honey Bee.  Harvard University Press.  Cambridge, MA

Regards,
Adony