DTPA (diethylenetriaminepentaacetic acid)-extractable Fe, Mn, Cu,
and Zn were determined an several neutral and calcareous soils dried at
various temperatures. Extractable Fe increased linearly over the drying
temperature range 22 to 100°C, whereas Mn increased in an irregular
manner. Values for Cu and Zn changed only slightly over this temperature
range. Extractability of an four elements increased when fieldmoist
samples were air dried; Fe by a factor of 2 to 3, and Mn, Cu, and
Zn by a factor of about 1.3 to 1.5. The increases in extractable Fe and
Mn appear to result from separate temperature and dehydration effects
and are only partially reversible with rehydration and moist incubation.
The results of this study indicate that sample handling be standardized
for calibration and routine tests before DTPA-extractable Fe and Mn
can be used as reliable diagnostic tests for these elements. Close control
of drying conditions for Zn and Cu analysis may be desirable but is not
as critical as for Fe and Mn
