1 Institute of Geography, Department for Soil Science and Soil Ecology, Ruhr-Universität Bochum, Universitätsstr. 150, D-44780, Bochum, Germany. volker.haering@gmail.com.
2 Organic Plant Production and Agroecosystems Research in the Tropics and Subtropics, Universität Kassel, Steinstr. 19, D-37213, Witzenhausen, Germany.
3 Institute of Geography, Department for Soil Science and Soil Ecology, Ruhr-Universität Bochum, Universitätsstr. 150, D-44780, Bochum, Germany.
4 Department of Soil Science, University of Ghana, Accra, Ghana.