Hopkins, C. G. (1910). Soil fertility and permanent agriculture. Ginn.
Lua i Stíl Chicago (17ú heag.)Hopkins, Cyril G. Soil Fertility and Permanent Agriculture. Boston, New York: Ginn, 1910.
Lua MLA (8ú heag.)Hopkins, Cyril G. Soil Fertility and Permanent Agriculture. Ginn, 1910.
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