The 150 mile radius is in the CDL section. Perhaps it only applies to vehicles that require a CDL to drive. http://info.sos.state.tx.us/pls/pub/readtac$ext.TacPage?sl=R&app=9&p_dir=&p_rloc=&p_tl oc=&p_ploc=&pg=1&p_tac=&ti=37&pt=1&ch=16&rl=3

Persons exempted from commercial driver license (CDL) requirements are:

(1) A person operating a vehicle that is controlled and operated by a farmer which is used to transport agricultural products, farm machinery, or farm supplies to or from a farm and which is not used in the operations of a common or contract carrier and used within 150 miles of the person's farm.