You can still use motion decoys in ND. We used six Mojo's this weekend in the stubble fields. They aren't (in my opinion) nearly as effective as they used to be. I remember when they first came out, ducks would drop out of the clouds to get to them. I've had ducks fly into them in the past and they would want to land directly underneath them, I don't see that any more.
You can't hunt in any standing/unharvested crops without the permission of the landowner. If there is access, without going through the crops, you can hunt the water.