How is the zakat calculated for land purchased for investment purposes that has been held for a full year?

Zakat is obligatory on land purchased for trade, by appraising it at market value each year, and 2.5% of its value is to be given as zakat if it reaches the nisab. As for land purchased for profit from its yield, zakat is obligatory on its rent if a year has passed over it and it has reached the nisab. The nisab for currency is what equals 85 grams of gold or 595 grams of silver.