The 25% limit controls how much you can deduct this year. It is not an overall limit on the deduction, just when you can take it.
For example, churches have a 60% limit--if your income is $100,000, you could theoretically donate $60,000 to your church and claim the entire amount as an itemized deduction on schedule A. However, since conservation expenses have a 25% limit, if your income is $100,000 and your expenses are $60,000, you can deduct $25,000 this year and the rest will carry forward (Turbotax does this automatically).
