For general property tax purposes including school tax purposes, the value of land which is actively devoted to agricultural, horticultural or forest use and which has been so devoted for at least the 2 successive years immediately preceding the tax year in issue, shall, on application of the owner, and approval thereof as provided in this section, be that value which such lands have for agricultural, horticultural or forest use; provided, that in the case of school taxes where such land is located in a public school district situated in 2 counties, the value of such land shall be that value arrived at by multiplying the value determined hereunder by the lower of the 2 general percentage rates of assessment in force in such counties for the tax year in issue.