"Extr_ap21"@en . . "Olsen (if pH > 7) resp. Mehlich (if pH < 7). Particularly used for available P." . . . . "Extr_ap21" . "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." . .