The DTPA‐Extractable Iron, Manganese, Copper, and Zinc from Neutral and Calcareous Soils Dried Under Different Conditions

Abstract

DTPA (diethylenetriaminepentaacetic acid)‐extractable Fe, Mn, Cu, and Zn were determined on 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 all four elements increased when field‐moist 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.