How does buying land affect my taxes?

If you itemize deductions, you will be able to deduct the real estate tax you pay.  The real estate tax deduction applies to all property you own.   There is a $10,000 deduction limit for state and local tax (SALT) paid. 

You will not be able to deduct mortgage interest. The mortgage interest deduction is only applicable to your primary and one second home.

The purchase of  property is no a tax event.  When you sell the property, you will have to report the sale and capital gain or loss.  The loss on personal use property (e.g. vacation home) is not deductible.  The loss on investment property is deductible.