Availability of trace elements from rocks and minerals.

Abstract

Fifteen rocks and 65 minerals were bioassayed for the amounts of Fe, Zn, Cu, Mn, and Mo available to Aspergillus niger. The micronutrients most commonly released were Fe and Mo, followed by Mn, then Cu, and least of all Zn. Some rocks and minerals contained traces of all micronutrient elements, but rarely in sufficient quantity for optimal growth of the mould. Among the rocks, the igneous types were better sources of micronutrients than the metamorphic and the sedimentary. Among the minerals, those featuring micronutrient elements in their chemical formulae tended to be fairly good suppliers of these elements, but certain minerals not suspected of containing micronutrients were also found to provide them in moderate amounts. The quantity of trace elements released from ferro-magnesium silicates varied considerably, so that they are imperfect indices of the micronutrient status of soils.