Columbia subject headings:
Agricultural innovations--United States.
Agricultural productivity--United States.
Harvard subject headings:
Agricultural conservation--United States.
Agricultural innovations--United States
Agricultural productivity--United States
Agriculture and state--United States.
Land capability for agriculture--United States.
Soil productivity--United States.
Princeton subject headings:
Agricultural conservation--United States.
Agricultural innovations--United States.
Agricultural productivity--United States.
Agriculture and state--United States.
Land capability for agriculture--United States.
Soil productivity--United States.