Pedosphere 30(3): 390--404, 2020
ISSN 1002-0160/CN 32-1315/P
©2020 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Nature of redox concentrations in a sequence of agriculturally developed acid sulfate soils in Thailand
1Department of Soil Science, Faculty of Agriculture, Kasetsart University, Bangkok 10900 (Thailand)
2School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley WA 6009 (Australia)
      Potential acid sulfate soils (PASS) are drained for agriculture, resulting in the formation of active acid sulfate soils (AASS), which gradually evolve into post-active acid sulfate soils (PAASS). Various redox concentrations (precipitates, costings, and mottles) occur in these soils as a result of pedogenic processes including biological activity and effects of land management. Although several studies have determined the mineralogy and geochemistry of ASS, the mineralogy and geochemistry of redox concentrations occurring in a sequence of ASS through PASS to PAASS have not been investigated. This study examined the mineralogy and geochemistry of redox concentrations and matrices within 5 PASS, 8 AASS, and 5 PAASS in Thailand. The labile minerals were predominantly controlled by oxidation status and management inputs. The unoxidized layers of PASS, AASS, and PAASS contained pyrite and mackinawite. The oxidation of Fe sulfides caused acidification and accumulation of yellow redox concentrations of jarosite and Fe (hydr)oxides at shallow depths. As the soils became well developed, they were recognized as PAASS, and the jarosite and goethite transformed to hematite. As ASS were drained, Co, Mn, Ni, and Zn moved downward and were associated with Fe sulfides and Mn oxides in the unoxided layer. Concentrations of As, Cu, Cr, Fe, and V did not change with depth because these elements became associated with jarosite and Fe (hydr)oxides in yellow and red redox concentrations, as well as the root zone, in the partly oxidized layer of AASS and PAASS. Arsenic was associated with pyrite under reducing conditions.
Key Words:  active acid sulfate soils,geochemistry,mineralogy,post-active acid sulfate soils,potential acid sulfate soils,trace metals
Citation: Sukitprapanon T, Suddhiprakarn A, Kheoruenromne I, Anusontpornperm S, Gilkes R J. 2020. Nature of redox concentrations in a sequence of agriculturally developed acid sulfate soils in Thailand. Pedosphere. 30(3): 390-404.
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