1. Physical fractionation of soil and organic matter in primary particle-size and density separates;Christensen;Advances in Soil Science,1992
2. Darwin, C., 1881. The Formation of Vegetable Mould through the Action of Worms with Observations in their Habits. Murray, London.
3. FAO, 1988. FAO/Unesco Soil Map of the World, Revised Legend, with Corrections and Updates. World Soil Resources Report 60. FAO, Rome (reprinted with updates as Technical Paper 20, ISRIC, Wageningen, 1997).
4. Glaser, B., 1999. Eigenschaften und Stabilität des Humuskörpers der Indianerschwarzerden Amazoniens. Bayreuther Bodenkundliche Berichte 68.
5. Black carbon in soils;Glaser;Organic Geochemistry,1998