بسم الله الرحمن الرحيم
By partnership if you intended to do business then whatsoever is bought with the joint money it shall be called business goods. Zakah is wajib on the business goods and cash in hand.
What is the nature of the land mentioned in the question? Was it bought with joint money with the intention of business? If it is so, then each year zakah shall be wajib on its market price. Further, whatsoever amount you own you will have to pay its zakah.
Note: Zakah is wajib on the owner, it is related to ownership. It does not have any relation with the name in paper. Though the name should be corrected i.e. the name should be of the person who is the real owner.
Allah knows Best!
Darul Uloom Deoband