If the lands are used for agriculture purposes, they are not subject to Zakat. The produce is subject to Zakat at the rate of 5% or 10% depending on irrigation.
If the property or land is acquired for resale or rent or any other investment, they are subject to Zakat at the anniversary of your year at the rate of 2.5% and it is calculated on the market value of the property on the Zakat day.
A property you live in or a land acquired to build your residence or residence for your parents is not subject to Zakat even if you did not yet start the construction.