Aj. Neary et Sr. Barnes, THE EFFECT OF SAMPLE GRINDING ON EXTRACTABLE IRON AND ALUMINUM IN SOILS, Canadian Journal of Soil Science, 73(1), 1993, pp. 73-80
Pyrophosphate-, dithionite- and acid ammonium oxalate-extractable Fe a
nd Al are often measured on a finely ground aliquot of soil. Grinding
provides a homogeneous sample from which a representative subsample ca
n be obtained at sampling aliquots of less than 1 g. When a significan
t portion of the unground soil is greater than the sieve mesh size use
d when grinding, abrasion of primary minerals may cause increased leve
ls of extractable Fe and Al. This study examined the distribution of e
xtractable Fe and Al in some sandy soils and compared their levels in
samples ground to < 500 mum and < 150 mum with those in unground < 2-m
m soil. Samples ground to < 150 mum yielded the highest amounts of ext
ractable Fe and Al. This effect was most prevalent when a motorized mo
rtar and pestle was used. Samples ground to < 500 mum, which were freq
uently re-sieved to avoid over-grinding, contained similar amounts of
extractable Fe and Al as the unground < 2-mm sample. If less than 1 g
of soil is used for analysis, a sample manually ground to < 500 mum (3
5 mesh) is advisable and a protocol for sample grinding is recommended
.