FWIW.... the following are my observations......merely to give you another perspective:

For what its worth I did a year end tax run through yesterday. I bought a new tractor this year. A local canning company rented the tractor before I got it although the deal was made prior to them using it. Tax gal said I could depreciate it or use Section 179. I probably couldn't use "Bonus Depreciation" on it since it might be considered "used".

Tractor would be considered used....original use did not commence with you..........so can only 179 it (or reg depr).

 I had Ag Leader equipment installed on the tractor and planter for a total of some $26000. This was done by another dealer. I had listed all this under repairs. She felt that some of the parts added to the planter could be considered repairs but that others and the parts on the tractor should technically be listed with the cost of the tractor. 

Sounds to me as if the Ag Leader equip should be handled as a totally separate line item for depr.......if the equip is an integral part of the tractor, so that it cannot be taken off and moved to a different tractor, then it would possibly be a part of the new tractor.......I would bet however that if that tractor gets moved down the road, you will switch the equip to another, unless the buyer ALSO wants the Ag L equip.  If an integral part of the tractor----- did the addition add to the resale or tradein value of the tractor.....significantly?.......I would bet not.

Since it would be depr separately, then the actual NEW (you are the original user) elements would be subject to bonus depr, so you would not have to use up all your 179 limit.

 If I use section 179 completely on the tractor, I guess this doesn't make much difference on the bottom line for the Federal Tax.

The rub with Section 179 here in Minnesota is that they don't allow all of it in the first year for computing Minnesota Income Tax. As I understand it, 80% of the amount used on the Federal side is added back in for the current year for the state side. You are able to use this in future years but it tends to stretch out the depreciation. I guess you could say that this means that a Section 179 item such as my tractor amounts to a 5 year depreciation for the State of Minnesota. I do have some of this "left over" depreciation on the Minnesota side from purchases in the past on other items which will help this year. This screwy setup essentially means that a piece of machinery might have two levels of depreciation associated with it.

Yes, Iowa does not "couple" with Fed for bonus depr.....does with 179, but not bonus, so we use up the 179 and leave bonus out of the picture if we can.......really sucks, but in the age of computers, the software does finally print out a "differences" sheet so it can be monitored.......but it still SUCKS.

I did do some tiling  (new not repair). She said that I should use Section 179 on that since I would get full use of it in 2013 on the Federal Side but a 5 year depreciation under the above on the Minnesota side. This would be in contrast to the 15 year straight depreciation that is normally used for new tile. If the tiling was considered repair then I could claim it all as repairs on both sides for 2013.

I agree with the gal.......but I would use 179 (and bonus if necessary) on it before the tractor, merely since the tile would have a longer useful life.  So, if are hitting the 179 limit......probably will want to take 179 on the tile first.  However...a complicating factor is also at what quarter in year did the majority of purchases occur------ I would bet your tax person has already considered that, however.

 For the new track situation, I would think that if the tractor originally had tracks and they were replaced then this would be a repair item. If the tractor was a wheel tractor converted to tracks then I'm not so sure. I think I'd go with repairs.

As indicated further below.......no option on the tires/tracks.

Lastly, I cannot remember what the tax rate(s) are for MN.......but the Federal rates will be at least 15% income, and 15% self employment = 30%.......... so, even though it is a hassle, having to use "two depr schedules" due to the lack of coupling is most likely a small price to pay to shorten the fed tax bill.