(a) Predominance. Highly erodible land shall be considered to be predominant on a field if either:

(1) 33.33 percent or more of the total field acreage is identified as soil map units which are highly erodible; or

(2) 50 or more acres in such field are identified as soil map units which are highly erodible.

(b) Modification of field boundaries. A person may request the modification of field boundaries for the purpose of excluding highly erodible land from a field. Such a request must be submitted to, and is subject to the approval of, FSA. FSA shall use the technical determination of NRCS in approving this request.

(c) Impact of changing field boundaries. When field boundaries are changed to include areas of land that were included in a field that was previously determined to be predominately highly erodible according to paragraph (a) of this section, such areas shall continue to be subject to the requirements for predominately highly erodible fields, except as provided in paragraph (b) of this section.

(d) Small area of noncropland. Small areas of noncropland within or adjacent to the boundaries of existing highly erodible crop fields such as abandoned farmsteads, areas around filled or capped wells, rock piles, trees, or brush which are converted to cropland are considered to meet the requirement of § 12.5(a)(2) if they are included in an approved conservation plan for the entire highly erodible field.