A COMPARISON AMONG NINE CANADIAN LABORATORIES OF DITHIONITE-, OXALATE-, AND PYROPHOSPHATE-EXTRACTABLE Fe AND Al IN SOILS

The results of two studies are reported: (1) a comparison of colorimetric and atomic absorption measurements of Fe and Al in dithionite, oxalate, and pyrophosphate extracts of soils; and (2) a comparison among nine Canadian laboratories of measurements of dithionite-, oxalate-, and pyrophosphate-extractable Fe and Al in six soils. Colorimetric and atomic absorption analyses gave the same measurements of Fe and Al in dithionite, oxalate, and pyrophosphate extracts of soils. Data reported by six Canadian laboratories showed close agreement; data reported by three laboratories showed poor agreement, indicating a need for reference soil samples containing known amounts of extractable Fe and Al to standardize laboratory procedures. Atomic absorption analysis of the extracts is much more rapid than colorimetric analysis and details of the atomic absorption methods are appended.