Use of the test-mineral technique to distinguish simple acidolysis from acido-complexolysis in a Podzol profile

• Published in: Geoderma 2007-01, Vol.137 (3), p.293-299
• Main Authors: Van Rompaey, K., Van Ranst, E., Verdoodt, A., De Coninck, F.
• Format: Article
• Language: English
• Subjects: Acido-complexolysis; Agronomy. Soil science and plant productions; Biological and medical sciences; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Podzol; Simple acidolysis; Soils; Surficial geology; Test-mineral technique
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2006.08.014

A test vermiculite was inserted in different horizons of a Podzol profile to study its behavior in contact with the organic solutes in the soil solution. After incubation in the soil for three years, the ECEC showed a clear negative correlation with the contents of Tamura extracted Al. XRD analyses confirmed the presence of Al-polymers blocking the minerals interlayer. The formation of these stable Al-polymers is in contradiction to the theory that acido-complexolysis and not simple acidolysis is one of the major soil forming processes in Podzols, preventing Al-interlayering in open 2:1 phyllosilicates by the strong complexing power of the organic acids present. The hypothesis that podzolization is no longer active in the studied profile so that the complexing acids, typical of the acido-complexolysis are no longer present in large enough quantities to prevent “aluminization” of the vermiculites had to be rejected after studying the chemical composition of the soil solutions. Significant amounts (∼ 75%) of dissolved aluminium proved to be strongly bound to organic acids, indicating an active podzolization process. The behaviour of test-minerals as a criterion to distinguish acidolysis from acido-complexolysis must thus be used with great care and should never be interpreted without detailed analysis of the soil solution. Where aluminium is present in the soil solution, the use of test-minerals is likely to fail to distinguish simple acidolysis from acido-complexolysis, as the conditions in the field are then too different from those during the laboratory experiments from which the theory on simple acidolysis/acido-complexolysis originally was derived and where the sole source of Al was the mineral itself.