7 C.F.R. § 718.109 – Deductions.

(a) Any contiguous area which is not devoted to the crop being measured and which is not part of a skip-row pattern under § 718.108 shall be deducted from the acreage of the crop if such area meets the following minimum national standards or requirements:
1. (1) A minimum width of 30 inches;
2. (2) For tobacco—three-hundredths (.03) acre. Turn areas, terraces, permanent irrigation and drainage ditches, sod waterways, non-cropland, and subdivision boundaries each of which is at least 30 inches in width may be combined to meet the 0.03-acre minimum requirement; or
3. (3) For all other crops and land uses—one-tenth (.10) acre. Turn areas, terraces, permanent irrigation and drainage ditches, sod waterways, non-cropland, and subdivision boundaries each of which is at least 30 inches in width and each of which contain 0.1 acre or more may be combined to meet any larger minimum prescribed for a State in accordance with this subpart.
(b) If the area not devoted to the crop is located within the planted area, the part of any perimeter area that is more than 217.8 feet (33 links) in width will be considered to be an internal deduction if the standard deduction is used.
(c) A standard deduction of 3 percent of the area devoted to a row crop and zero percent of the area devoted to a close-sown crop may be used in lieu of measuring the acreage of turn areas.