As a hedge against inflation, a tractor would be a poor choice. They lose value the minute you take delivery of them...thousands less than you paid. Even if their value increases with inflation, it's not going to make up the thousands they initially lose. If you're not factoring in the cost of renting a machine when needed, the convenience factor, etc....just the straight "investment" potential, it's not really hard to figure.
People will say "I bought a tractor for $15,000, used it for ten years and sold it for $15,000, so it didn't cost me anything." That's not true. Because of inflation they lost money.
I used an inflation calculator and picked the year 2000 and the year 2010 to figure out what it would be for the $15,000 tractor I mention here. To be dead even, you'd have to sell the tractor for $19K in 2010. I don't see that happening very often. In the example above, the person selling the tractor for what they paid lost $4K on the deal. Granted, they had the use of the machine, but that's a different topic.
In short, buying a tractor isn't an "investment" it's an expense. Yes, commercial farmers are "investing" in their business when they buy equipment, but the equipment itself is not an investment, it's a business expense that they get a tax credit for. There's essentially no chance they will sell the equipment for more than they paid for it, corrected for inflation, down the road.
Other than retail sales, the only reliable way to make money on equipment would be if you bought something used that needed significant repairs you are capable of performing yourself, getting it all fixed up, and selling it.