Is zakat obligatory on commercial lands and buildings that are not utilized or have an irregular income, and how is it calculated if cash is not regularly available?

Zakat is obligatory on commercial lands that were purchased with the intention of trade. This is done by appraising them at the completion of a full lunar year (hawl) from the original capital with which they were purchased, and giving out a quarter of a tenth (2.5%) of their value. As for other wealth, zakat becomes obligatory on it if it reaches the nisab either by itself or by combining it with other cash or commercial lands, and a full lunar year passes over it. A quarter of a tenth is also to be given from it. If the wealth falls below the nisab due to spending on necessities, then there is no zakat on it.