I presume the Deputy is referring to the windfall tax rate of 80% which applies to disposals of rezoned land where both the rezoning and the disposal take place after 30 October 2009. The windfall tax applies to the portion of any profit or gain which arises from the rezoning. The balance of the profit or gain is taxable at the appropriate income tax, corporation tax, or capital gains tax rate, depending on the circumstances of the disposal.
In most cases a site of agricultural land will not require rezoning to allow the building of a house, so the windfall tax rate would not apply to the disposal of such land. However, to put the matter beyond doubt, Finance Bill 2010 contains a measure providing that the windfall rate will not apply to sales of sites up to 1 acre in size and €250,000 in value.