Free space that separates a GM field from a non-GM field
To prevent the out-crossing of GM crops in adjacent conventional or organic fields, isolation distances are one proposed tool for co-existence. The idea is to keep a distance between GM and other fields wide enough to allow for most of the GM pollen to fall to the ground without pollinating crops in the conventional or organic field.
Depending on the permitted maximum threshold of GMOs in the harvest, researchers have come up with different recommendations, reaching from 25 to 250 metres for maize. For other crop species, little data is available at the moment. Factors influencing the recommendations besides the threshold value are the pollen weight (i.e. the crop species), wind direction, field size and shape, but also weather conditions.