552 Subfield $k - Beginning and ending dates of attribute values:

Subfield $k contains the earliest and latest dates for which the attribute values are valid. The date is expressed in four digits.

Example:

552 ##$asoil type$bsoil mapping unit polygon (SCS)$cnumbered$dsoil category, user-defined$g1-4$jinteger$k19940809-19940812$luntested.