Below is an excerpt form the Sales and Tax Use Bulletin from the Texas Comptroller. See the complete bulletin here.

All-Terrain and OffRoad Vehicles Off-road vehicles are self-propelled vehicles designed for use off of public streets and highways. Examples include dirt bikes, golf carts, all-terrain vehicles (ATVs), utility vehicles and other vehicles not designed or intended by the manufacturer to meet motor vehicle registration and safety inspections. Motor vehicles designed for on-road use, such as cars, pick-ups, trucks and trailers, are subject to state motor vehicle tax under Chapter 152 of the Tax Code. See Motor Vehicle Tax for information about the taxability of motor vehicles. Off-road vehicles are subject to state and local sales and use taxes.

ATVs and utility vehicles may qualify for the agricultural sales tax exemption if used exclusively on a commercial farm or ranch in the production of agricultural products for sale. The exemption does not apply to vehicles like golf carts and miniature motorcycles that are designed and intended for recreational use. ATVs and utility vehicles used for any purpose other than producing agricultural products for sale, like hunting, or that are used at any location other than a commercial farm or ranch do not qualify, even if the vehicle is also used in the production of agricultural products.

For example, a utility vehicle used exclusively on a farm to perform crop spraying or feeding cattle qualifies for the exemption; however, if the vehicle is also used for hunting or pleasure riding, it does not qualify. A purchaser claiming the agricultural exemption on the purchase of an ATV or utility vehicle must provide a properly completed exemption certificate to the seller at the time of purchase, and after Jan. 1, 2012, must include a valid Ag/Timber Number.

For purchases made prior to Jan. 1, 2012, the exemption certificate issued by the purchaser must state that the vehicle will be used exclusively on a farm or ranch for a qualifying use. General statements such as “use on a farm” are not valid statements for exemption. If an ATV or utility vehicle that was purchased tax free for use exclusively in agricultural production is used in any non-qualifying manner, the exemption is lost and the purchaser is responsible for remitting tax on the original sales price of the item directly to the Comptroller.