Solid-state 'ANTIPOT.13 C' nuclear magnetic resonance characterisation of humic acids extracted from Amazonian dark earths (terra preta de índio) - Novotny, E. H.; Bonagamba, Tito José; Azevêdo, Eduardo Ribeiro de; Hayes, M. H. B. (Amazonian Dark Earths: Wim Sombroek's vision, 2009)