MT Code 15-1-101: The term "agricultural" refers to: 
     (i) the production of food, feed, and fiber commodities, livestock and poultry, bees, biological control insects, fruits and vegetables, and sod, ornamental, nursery, and horticultural crops that are raised, grown, or produced for commercial purposes; and ....

MT Code 15-7-202: Contiguous parcels of land totaling 160 acres or more under one ownership are eligible for valuation, assessment, and taxation as agricultural land each year that none of the parcels is devoted to a residential, commercial, or industrial use.

The deadline to file for an agricultural classification is March 1st.