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 did not intend to allocate this piece of land for trading purposes when you had first possessed it, then no Zakah is due on it because it is not considered tradable goods, but rather it is designated for personal possession. In fact, it would not be considered tradable goods even if you changed your intention and intended to sell it for profit afterwards.
However, if you bought it for the purpose of making it an object of trade, it would be considered tradable goods and you are required to pay its Zakah. The Hanbali scholar Al-Hajjaawi wrote about trade goods, “The item of property is not considered tradable goods unless the owner possesses it by means of his actions with the intention of selling it at a profit either by way of compensation, such as the case of selling it in exchange of a value, or without compensation, such as the case of a non-conditional gift and spoils of war … If the owner took possession of the item of property through inheritance or by means of his actions without an intention (of selling it) and then held the intention of trading and selling it for profit afterwards, it would not be considered tradable goods …” [Al-Iqnaa‘, adapted]
The author of Al-Rawdh Al-Murbi' says, “If the owner takes possession of the item of property by means of his actions, such as through purchase, marriage, Khul’, acceptance of a gift, bequest, or recovery of sold item, while holding the intention of trading in it at a profit and continues to hold such an intention until he receives the profits through sale or any other action and the profits reach the due Nisaab (i.e. minimum amount eligible for Zakah) of gold or silver, he has to pay its Zakah. If one takes possession of the item of property through inheritance or by means of his actions and then holds the intention of trade and sale at a profit afterwards, it is not considered tradable goods..."
In the latter case, Zakah is required for the piece of land for each year that passes while it is in your possession as long as its value reaches the Nisaab. If so, you should pay 2.5 % of its value. The fact that you intend to give the profit in charity does not waive the obligation of paying the due Zakah.