Is it permissible to count the amount paid with the intention of zakat for land—which later turned out not to be subject to zakat—as part of the due zakat on monetary assets?

First: There is no Zakat due on land unless it is for trade.

Second: It is not obligatory to specify the wealth for which Zakat is being paid. However, if it is specified, it becomes designated. So, if one gives Zakat with the intention that it is for a specific wealth, and then that specific wealth is found to be destroyed, it is not permissible to transfer the Zakat to another wealth, because the intention was attached to the first wealth. But if one gives Zakat with a general intention without specification, and then one of the wealths is destroyed, it is permissible for him to make the Zakat for the remaining wealth.