Columbia subject headings:
Agriculturists--Germany--Biography.
Agriculturists--Germany--Oldenburg (Landkreis)--Biography.
Oetken, Friedrich, 1850-1922.
Harvard subject headings:
Agriculturists--Germany--Biography.
Agriculturists--Germany--Oldenburg (Landkreis)--Biography.
Oetken, Friedrich, 1850-1922.
Princeton subject headings:
Agriculturists--Germany--Biography.
Oetken, Friedrich, 1850-1922.