Christiansen, S. (1981) “Hans Ruthenberg: FARMING SYSTEMS IN THE TROPICS 3rd ed. Oxford 1980, XXII, 424 s., ill., 24 cm, paperback £ 12.50. Oxford University Press”., Geografisk Tidsskrift, 81. Tilgængelig hos: https://tidsskrift.dk/geografisktidsskrift/article/view/45228 (Set: 6 december 2025).