. "Extr_ap20" . "Olsen (not acid soils) resp. Bray I (acid soils). Particularly used for available P." . . "Leenaars J.G.B., A.J.M. van Oostrum and M. Ruiperez Gonzalez, 2014. Africa Soil Profiles Database, Version 1.2. A compilation of georeferenced and standardised legacy soil profile data for Sub-Saharan Africa (with dataset). ISRIC Report 2014/01. Africa Soil Information Service (AfSIS) project and ISRIC - World Soil Information, Wageningen, the Netherlands. See Annex 4." . . . . "Extr_ap20"@en .