(9) Field .— The term “field” means a part of a farm that is separated from the balance of the farm by permanent boundaries such as fences, roads, permanent waterways, or other similar features. At the option of the owner or operator of the farm, croplines may also be used to delineate a field if farming practices make it probable that the croplines are not subject to change. Any highly erodible land on which an agricultural commodity is produced after December 23, 1985 , and that is not exempt under section 3812 of this title , shall be considered as part of the field in which the land was included on December 23, 1985 , unless the owner and Secretary agree to modification of the boundaries of the field to carry out this chapter.
16 USC § 3801(a)(9)
None identified, default scope is assumed to be the parent (subchapter I) of this section.