........................what you were actually trying to say is to tax owners who deliberately keep their lands wasted, typical of what feudal lords do...
tell you 80% agricultural feudal lords are in parliament, they dont allow even to tax on cultivated lands, let alone what you are thinking... which is not very reasonable either... against private ownership rights,
however, inheritance laws if strictly implemented, can reduce the size of these lands owned by one person or so, on the other hand empowerment of their "Raiyat" can be done without conflict, through lending these tenants 2-5 acre government land on lease, and directly purchasing the production from them...
as far as Taxation is concern the strategy for a proper taxation is on Income, if Income is properly channelized through accounts, by developing this mechanism it is easy to deduct Income tax.
currently you donot know how much a person earns, nor you know how much other lands/businesses he own through law of "bay-nami" as its purely dependent on personal honesty...