Mass. Gen. Laws ch. 61A § 4
For general property tax purposes, the value of land, not less than five acres in area, which is actively devoted to agricultural, horticultural or agricultural and horticultural uses during the tax year in issue and has been so devoted for at least the two immediately preceding tax years, shall, upon application of the owner of such land and approval thereof, be that value which such land has for agricultural or horticultural purposes. For the said tax purposes, land so devoted shall be deemed to include such contiguous land under the same ownership as is not committed to residential, industrial or commercial use and which is covered by application submitted pursuant to section six. Land shall be deemed contiguous if it is separated from other land under the same ownership only by a public or private way or waterway.
Land under the same ownership shall be deemed contiguous if it is connected to other land under the same ownership by an easement for water supply. All such land which is contiguous or is deemed contiguous for purposes of this chapter shall not exceed in acreage one hundred per cent of the acreage which is actively devoted to agricultural, horticultural or agricultural and horticultural uses.
The rate of tax applicable to such agricultural or horticultural land shall be the rate determined to be applicable to class three, commercial property under chapter fifty-nine.
Mass. Gen. Laws ch. 61A, § 4