Even if you end up running on them some, you probably won't be able to tell later in the season.  If it's a tandem axle spreader and you run right on the row, that might be a different story.  If you have duals, by all means make sure that they're on.  I would wait until they have their first trifoliate showing, then do the spreading on a warm afternoon. 

Any idea what the fertility is like on this farm?  There's a good chance that you could leave them go and do your fertilizing in the fall for next year and your crop removal and it wouldn't make any difference to this years crop.

Mike