Columbia subject headings:
Agricultural conservation--United States--History--Statistics.
Agricultural conservation--United States--Statistics.
Conservation Reserve Program (U.S.)--History.
Soil conservation--United States--History--Statistics.
Soil conservation--United States--Statistics.
Harvard subject headings:
Agricultural conservation--United States--History--Statistics.
Agricultural conservation--United States--Statistics.
Conservation Reserve Program (U.S.)--History.
Soil conservation--United States--History--Statistics.
Soil conservation--United States--Statistics.
Princeton subject headings:
Agricultural conservation--United States--History--Statistics.
Agricultural conservation--United States--Statistics.
Conservation Reserve Program (U.S.)--History.
Soil conservation--United States--History--Statistics.
Soil conservation--United States--Statistics.
Statistics.