بسم الله الرحمن الرحيم
If you bought the plot with the intention of business then this plot turned to be business material. And zakah will be wajib on its value each year. And if you intended to keep it for children or in case you need some money then you may also sell it and fulfill your need, so in all these cases zakah will not be wajib on the plot.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.