1. Blume H-P (1965) The characterisation of humus compounds by litter and humus group analysis with regard to morphological properties. J Plant Nutr Soil Sci 111:95–113
2. Blume H-P, Felix-Henningsen P, Fischer WR, Frede H-G, Horn R, Stahr K (eds) (1996) Handbook of soil science, ecomed, Landsberg. Wiley-VCH, Weinheim (in German)
3. Jenny H (1941) Factors of soil formation. McGraw-Hill, New York
4. Alaily F (2008) Das Herz der Sahara – Das trockenste Gebiet der Erde. Cornelius, Halle/Saale. Several photos of soils
5. Altermann M, Kühn D, Bodensystematik AG (1999) Systematik der bodenbildenden Substrate; Kap. 3.2.8 in Blume et al. (1996ff)