Wa `alaykum as-salamu wa rahmatullahi wa barakatuh.
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
Dear brother, thank you for your question that shows your interest to know more about the teachings of Islam and your concern to carry out your religious duties.
It should be clearly known that the criterion of zakah is based on whether the person is rich or not. If he or she has an amount of money that reaches that nisab (zakatable amount), he has to pay the due zakah for this amount according to the kind of possession he owns.
In his response to your question, Prof. Dr. Monzer Kahf, Professor of Islamic Finance and Economics at Qatar Faculty of Islamic Studies, states:
The criterion is whether you are rich or not. Suppose a business not only did not make income but made losses, but it is still above the nisab? The answer is YES, of course, and every year. If you are rich being an owner of these two lots of land that you do not need them for your actual living, then they are subject to zakah regardless of what people may say or claim. It is a property that you own and it makes you rich, it is a mal (money) for you and Allah said that mal is subject to zakah (see Verse 9:103).
Coming to details, land used in agriculture is exempt and agriculture products are subject to zakah at the rate of 5% or 10%. If it is not agricultural, it is then either used for your residence (then it is exempt too), or an item of your wealth then it is subject to zakah.
Allah almighty knows best.