There must be some serious variables with this. ?

 I would imagine one big variable would be the moisture content at time of tillage and the type of tillage.?

 "Here", if you walk a wheat field in july, the conventionally tilled fields will be so dry and cracked open you can not get a pick axe to penetrate. If you pound at it long enough, you will find no moisture with in the root zone. The no-till, and I mean no-till, not reduced tillage or minimum till, but actual no-till or single disk planting only, you can still find moisture with in the root zone. That is with the crop being planted on the same spacings and at approx. the same time.