The short answer is yes.  The long answer is yes plus all this ...

Do a search of the forums for the keyword DOT for the last 6 months and you will find several discussions with information you don't want to hear. A friendly DOT inspector told one farmer "you need: Medical card, USDOT # and have it on the truck, have Inspection stickers on both the truck and trailer, and be ready for an inspection".  You don't want to consider what an unfriendly DOT inspector might have done. And if you are going out of state you will need an IFTA fuel sticker as well. If you are hauling something that needs placarded as hazardous material ... you may just want to hire it hauled for you.

A couple good ones to start with are:

Do I need a DOT # as a farmer in IL?

http://talk.newagtalk.com/forums/thread-view.asp?tid=90847&posts=16&highlight=DOT&highlightmode=1#M647543

and

Interstate Commerce - Medical Card, Inspection, USDOT #, 24,000# GVCWR OH MY!!!

http://talk.newagtalk.com/forums/thread-view.asp?tid=95380&posts=7&highlight=DOT&highlightmode=1#M677356