There are a number of practical factors, however, that minimize pollen mixing. The pollen load in a field is usually great enough so that it will not allow significant levels of outside pollen to impact the crop. In addition, in a dominant gene system, such as that used to produce hybrids with the Bt gene, only half the pollen in the Bt commercial field contains the Bt gene. Only half the pollen that can possibly drift from a field of commercial corn hybrids with the Bt gene has the Bt gene. Pollination timing varies from field to field, depending on planting date, maturity of the hybrid and the weather.
Pollination typically lasts only from five to ten days.
Fields next to each other may pollinate at different times. How pollen travels depends on environmental factors, such as the wind, temperature and humidity. These, of course, vary from season to season, from area to area. Distance minimizes pollen contact. The farther apart fields are, the less likely their pollen can mix.