It depends on what the tractor is used for.  If it is used in your trade or business (other than farming), you can deduct it as a business expense on your business tax return (Form 1040, Schedule C, Form 1065, 1120 or 1120-S as appropriate in your circumstance).  If you use it in your farming operations, you can deduct it on Schedule F.  If you use it for personal reasons outside of business, then it is not deductible.