You can carry over your contributions that you are not able to deduct in the current tax year because they exceed your adjusted-gross-income limits. You can deduct the excess in each of the next 5 years until it is all used, but not beyond that time. Your total contributions deduction for the year to which you carry your contributions cannot exceed 50% of your AGI for that year.
A carryover of a qualified conservation contribution can be carried forward for 15 years.
Contributions you carry over are subject to the same percentage limits in the year to which they are carried.
For each category of contributions, you deduct carryover contributions only after deducting all allowable contributions in that category for the current year. If you have carryovers from 2 or more prior years, use the carryover from the earlier year first.
For examples and more information refer to page 15 of Publication 526.