I just paid $300 for tarpaulins and plastic to cover my round bales or hay stacked in a field. Can those items be purchased tax-exempt?

Yes, if purchased by a qualified agricultural certificate holder, plastic and canvas coverings, including tarpaulins, can be purchased for use (1) in the care and raising of plants, seeds, or seedlings; (2) for cover for agricultural and horticultural products, including hay; and (3) to cover a silo or grain bin or other similar structures are exempt from tax.