There are also some forest soils of more recent times that cannot clearly be classified as Alfisols or as Spodosols because, despite their sandy horizons, there are not nearly acidic enough to have the typical features of a Spodosol.
22.
Pedalfer is a formative element in the United States soil taxonomic system for the Alfisols soil order . " Alf " is the formative element in the Alfisol name, and refers to aluminium ( Al ) and iron ( Fe ).
23.
With the aid of X-ray diffraction, paleosols can now be classified into one of the 12 orders of Soil Taxonomy ( Oxisols, Ultisols, Alfisols, Mollisols, Spodosols, Aridisols, Entisols, Inceptisols, Gelisols, Histosols, Vertisols and Andisols ).
24.
Because of the changes in the Earth's climate over the last fifty million years, soils formed under tropical rainforest ( or even savanna ) have become exposed to increasingly arid climates which cause former oxisols, ultisols or even alfisols to dry out in such a manner that a very hard crust is formed.
