COMPARISON OF AMMONIUM BICARBONATE-DTPA, AMMONIUM CARBONATE, AND AMMONIUM OXALATE TO ASSESS THE AVAILABILITY OF MOLYBDENUM IN MINE SPOILS AND SOILS

A variety of extractants has been used to assess the availability of m olybdenum (Mo) in soils. Most of the extractants have been studied fro m a deficiency aspect rather than for soils with Mo toxicity, and none of them have been used to extract available Mo from mine spoils. The purpose of this study was to examine the potential of different chemic al extractants for assessing the availability of Mo in mine spoils and soils. One mine spoil and three soils were treated with sodium molybd ate and then subjected to wetting and drying cycles for two months. Th ese spoil/soils were extracted with ammonium bicarbonate DTPA (AB-DTPA ), ammonium carbonate, and ammonium oxalate solution for available Mo. Crested wheatgrass (Agropyron cristatum) and alfalfa (Medicago sativa ) were grown in the spoil/soils in a greenhouse to determine plant upt ake of Mo. Additionally, four mine spoils and six soils were extracted and analyzed for available Mo as mentioned above. The results obtaine d by these three extractants were highly correlated. It was found that ammonium oxalate extracts the greatest amount of Mo among the three e xtractants from spoil/soils since it dissolves some adsorbed Mo from F e-oxide and Al-oxide. The changes in pH of spoil/soils did not have a significant effect on the amount of Mo extracted by any of these metho ds. The relationships between Mo uptake and Mo extracted by each metho d were all significant at 1% level. None of the extractants were clear ly better or worse than the others. All three methods can be used to a ssess Mo availability, and potential toxicity from plant uptake of Mo from reclaimed spoils.