The answer depends on the intention with the land.

If the land has simply been inherited or purchased with no particular intention or as a store of wealth, then no Zakat is due.

If it was bought for investment, meaning capital appreciation purposes specifically, then Zakat is due on the approximate sale price of the land every year. One can delay the payment for each year for the time when the land is actually sold. In this case it will be due for each of the previous years based on the land value at the time.
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