All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
If you bought this land to possess it, no Zakah is due on it. If you bought it for the purpose of selling it, then it takes the ruling of trade goods and you have to assess it on the day when a full lunar year had passed since you bought it. You have to pay a rate of 2.5% of its value annually as its Zakah. However, if you were hesitant either to possess or sell it when you first bought it, then see which of the two options was closer to your intention and apply the relevant ruling. Moreover, if you intended to possess it for a fixed period of time during which you had no intention to sell it, then you later made up your mind to sell it, you have to pay the Zakah on its value once a lunar year has passed since the time you intended to sell it.
Allaah Knows Best.