Hmm, never heard of pullets eating dirt, unless they were looking for some kind of grit but you say they have plenty access to that. Sounds like they may be missing protein. Mine gorge before entering the coop at night, as well, but I have a container mixed with Laying Pellets and crumbles, as well as some Chick Starter and about a cup full of crushed corn, mixed in with it and I've never seen them eating dirt.