We highly recommend this article, The Biology of Soil Compaction (pdf), revised and updated from an Ohio State* publication, and consider it to be absolutely essential to understanding a no-till system. Indeed, it should be ‘required reading’ for anyone involved in farming. Or even gardening!
*The second author is Juca Sá, the famed Brazilian soil scientist.
Note: Exapta doesn’t endorse controlled traffic, although it’s mention is a minor blemish on a fabulous article. We suspect its mention is due to Randall Reeder’s long-standing advocacy for controlled traffic. Exapta respectfully disagrees, noting how devastating the water erosion becomes in the tracks in continuous no-till if there’s even the smallest slope.