The role of soil organic matter and short-range ordered aluminosilicates in controlling the activity of aluminum in soil solutions of volcanic ash soils

• Published in: Geoderma Vol. 137; no. 1; pp. 40 - 57
• Main Authors: Yagasaki, Yasumi, Mulder, Jan, Okazaki, Masanori
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 31-12-2006; Elsevier
• Subjects: Agronomy. Soil science and plant productions; Aluminum; Biological and medical sciences; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Soil organic matter; Soil solution; Soils; Surficial geology; Volcanic ash deposits; Japan; Soil organic matter; Volcanic ash deposits; Soil solution; Aluminum; stoichiometry; data; Support; chemical properties; complexing; acids; aluminosilicates; silicates; mechanism; Release; volcanic ash; Addition; accumulation; dissolution; Aluminium III Ions; Previous study; Volcanic soils; physicochemical properties; imogolite; pedogenesis; organic materials; alteration; equilibrium; kinetics; Acid base titration
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/j.geoderma.2006.07.001

Mechanisms controlling the activity of free aluminum (Al) in soil solutions and their implications for pedogenesis in two Japanese volcanic ash soils were investigated by means of acid-base titrations and kinetic studies of mineral dissolution. The A and AB horizons of both soils are rich in soil organic matter (SOM) and organically bound Al. In addition, short-range ordered aluminosilicates such as imogolite and proto-imogolite are abundant. Despite their abundance, the A horizons are undersaturated with respect to short-range ordered aluminosilicates, such as imogolite and proto-imogolite. This suggests low dissolution rate of these minerals, possibly due to alteration of the physico-chemical characteristics of their surfaces, caused by complexation with SOM. The AB horizons in both soils are close to equilibrium with short-range ordered aluminosilicates. The fast release of Al upon addition of strong acid to A horizons, combined with the reaction stoichiometry, observed in acid-base titrations suggests that the activity of Al
3+ and H
+ are controlled by complexation reactions with SOM. Furthermore, our data support previous studies indicating that SOM input in A horizon of volcanic ash soils dissolves short-range ordered aluminosilicates. Thus, simultaneous accumulation of SOM and depletion of short-range ordered aluminosilicates, due to leaching, are important long-term processes of the pedogenesis in soils developed from volcanic ash deposits.