Columbia subject headings:
Agricultural productivity--England--Hertfordshire--History.
Agriculture--England--Hertfordshire--History.
Harvard subject headings:
Agricultural productivity--England--Hertfordshire--History.
Agriculture--Economic aspects--England--Hertfordshire--History.
Great Britain--History--Medieval period, 1066-1485.
Hertfordshire (England)--Climate--History.
Princeton subject headings:
Agricultural productivity--England--Hertfordshire--History.
Agriculture--England--Hertfordshire--History.
Great Britain--History--Medieval period, 1066-1485.