1989 Fiscal Year Final Research Report Summary
Studies on Humus Complexes and Charge Characteristics of Volcanic Ash Soils in Tropics and Subtropics
| Project/Area Number |
62560065
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
土壌・肥料
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| Research Institution | University of Tsukuba (1988-1989)
Kagoshima University (1987) |
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Principal Investigator |
HIGASHI Teruo University of Tsukuba, Institute of Applied Biochemistry, Associate Prof., 応用生物化学系, 助教授 (20094170)
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| Project Period (FY) |
1987 – 1989
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| Keywords | volcanic ash soils / humus complexes / amorphous inorganic constituents / analysis of humus forms / allophane / ferrihydrite / imogolite |
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| Research Abstract |
Soil samples of 100 pedons, classified as Udands, Cryands, Perands, Ustands, Xerands and Vitrands, and Andic or Vitrandic subgroups in other orders, from seven countries under varying climatic conditions were studied with particular reference to: (1) humus accumulation and the formation of Al- and Fe-humus complexes; (2) the nature of Al- and Fe- humus complexes; and (3) the pedogenic significance of Al- and Fe-humus complexes.
The humus accumulation-time relationships and the significant positive correlations between T-C and Alpyr or (Al + 1/2Fe)pyr suggested that the accumulation and stabilization of humus in Andisols proceeded simultaneously with the formation of Al- and Fe-humus complexes, irrespective of the differing climatic conditions experienced by the pedons. Implication of Alpyr and Fepyr in humus accumulation in Andisols was further supported by the lack of correlation between T-C and Alox-pyr or (Al + 1/2Fe)ox-pyr. The Alpyr/Cpyr and (Al + Fe)pyr/Cpyr atomic ratios for samples of 33 Andisol pedons were 0.14 and 0.17 respectively, suggesting that both polymerized and monomeric hydroxy Al and Fe ions would be in close association with humus to form Al- and Fe-humus complexes. The accumulation of humus seems to retard the formation of allophane and imogolite, as indicated by the significant positive correlations between the ratio of (Al + 1/2Fe)pyr to (Al + 1/2Fe)ox and the content of T-C, and by the influence of humic substances on their formation. This retardation effect was greater for the humus present in non-Andepts than for that in Andepts.
The present results thus indicate that Al- and Fe-humus complexes merit close attention in our efforts to understand the pedogenesis and distinctive properties of Andisols, and that these complexes are very important in relation to andic soil properties in allic and/or melanic great groups in Udands and Cryands, and in Andic subgroups in other orders.
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