Extractable Fe in the surface horizons of a range of soils from Queensland

The levels of iron and aluminium extracted from 36 surface soils by pyrophosphate, oxalate and dithionite are compared with a number of other soil properties. Correlations suggest that aluminium released by these extraction procedures is largely associated with organic matter while only a small fraction of the iron released is in this form. Significant correlations between soil pH and the negative logarithms of both oxalate (r = 0.715) and pyrophosphate (r = 0.959) extractable iron in soils with >20% clay content indicate that pH is the most significant factor in determining the level of ferrihydrite and iron/organic matter complexes in surface soils. The significance of these relationships in terms of soil weathering processes is discussed. Further, the data suggest that pyrophosphate extractable iron is a useful indicator of the most active, mobile component of iron in surface soils.