effective when property tax burdens are higher. While it would be useful to determine the effects of deferred taxation, the results here suggest that the choice of deferred tax policy implementation was endogenous.
While 10 per cent is a significant amount of land, several caveats are in order before the results of this study can be interpreted as an endorsement for the policy. First, this study has not demonstrated cost-effectiveness. Various studies (for example, Regional Science Research Council ( 1976) and Hansen and Schwartz ( 1976)) have concluded that use-value assessment does indeed relieve tax burdens on farmers, 15 implying some combination of lowered jurisdictional revenue and burden shifting. One way to get a simple measure of the potential revenue that communities lose would be to get data from states that require dual assessments for rollback taxation purposes. If states have to keep track of tax liabilities under both assessments, the difference would be a measure of the cost of the policy. Collecting a large sample of such data may not be simple because most tax records are kept locally and are often not in an easily accessed database. Even if a cost estimate could be determined, it still begs the question of whether or not the preserved land is worth the cost. The problems of monetizing the scenic amenities of open space are manifest, and measuring the externalities thoroughly would have to include the negative externalities to farming, such as agrochemical run-off and air quality impacts from dust and livestock.
Furthermore, it is not at all clear that preferential assessment should apply to all agricultural land, regardless of the value of the positive externalities it generates. If the amenity derives from open space generally, rather than farmland in particular, the common practice of targeting the programme solely to productive farmland does not follow. Finally, areas of urban sprawl cannot rely on preferential assessment, taking decades to accrue its potential impact on land use, to preserve open space when tax burdens are minor compared with potential returns to development.