
Thaer (1810) cited in: Martin Frielinghaus and Claus Dalchow. " Thaer 200 years at Möglin (Germany) http://horizon.documentation.ird.fr/exl-doc/pleins_textes/ed-06-08/010039833.pdf." in documentation.ird.fr. (2007): 259-267.
Opening sentence of Thaer's four-volume Grundsatze der rationellen Landwirthschaft (Principles of Efficient Agriculture, 1809-1812).