GUILLET, D. W. Comparative irrigation studies: the Órbigo Valley of Spain and the Colca Valley of Perú. Polígonos. Revista de Geografía, [S. l.], n. 2, p. 141–150, 2005. DOI: 10.18002/pol.v0i2.1268. Disponível em: https://revpubli.unileon.es/ojs/index.php/poligonos/article/view/1268. Acesso em: 4 feb. 2023.