Analytical Methods:Fe Fractionation

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SASSA Home PageAnalytical Methods Home PageSpecialist Analytical TechniquesElement Fractionation Analysis ⇒ Iron Fractionation


[edit] Iron Fractionation

Summary table
ScaleLaboratory scale analysis, interpretation requires specialist knowledge
QuestionsIdentification of soil processes such as podzolisation and gleying
Samples and storageBulk samples are usually used, samples should be taken from each horizon / context vertically through a soil section.
Time and costFractionation methods are generally labour intensive and hence tend to be moderately expensive.


The form, distribution and total concentration of iron in soil is strongly affected by soil forming processes such as weathering, leaching, podzolisation and gleying (waterlogging). Identifying the effects of these processes are important in reconstructing past environmental conditions from buried soils. The effects of these processes can also have significant effects on the field appearance of deposits and on the distribution and concentration of a range of soil elements, not just iron. The possible occurence of podzolisation is also important if a deposit is to be radiocarbon dated as organic matter may be translocated down profile alongside iron.

The fractionation of iron from the iron rich spodic horizon, either using pyrophosphate is used as one of the tests to identify podzol soils in many soil classification systems. For example, in England and Wales (Avery, 1980) a spodic horizon should contain more than 0.3% iron extractable in potassium pyrophosphate (0.1M K4P2O7, Bascomb, 1974), and in the USDA and FAO systems aluminium + 1/2 iron concentration in an ammonium oxalate extract totalling 0.5% or more (Soil Survey Staff, 2006), or twice that in the overlying horizon (FAO, 1998).

Analysis of the extract can be made using a colorimeter or atomic absorption spectrophotometer, alongside appropriate standards and blank solutions.


[edit] References

  • Avery, B.W. (1980) Soil classification for England and Wales: higher categories. Harpenden, Soil Survey of England and Wales, Technical Monograph No. 14.
  • Bascomb, C.L. (1974) Physical and chemical analyses of <2 mm samples. In (Eds. B.W. Avery and C.L. Bascomb) Soil survey laboratory methods. Harpenden: Soil Survey of England and Wales, pp.14-41.
  • FAO (1998) World reference base for soil resources. Rome: ISSS-AISS-IBG.
  • Soil Survey Staff (2006) Keys to soil taxonomy. Washington: USDA, Tenth edition.


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