Aspergillus niger test is used for

Aspergillus niger test is used for Cu and Mg.
Aspergillus niger is a haploid filamentous fungus that is used for waste management and biotransformations in addition to its industrial uses, such as the production of citric acid and extracellular enzymes.
The use of Aspergillus niger (Mulder's M strain) as a test organism for determining Mg, Cu, Zn and Mo in soils, and the last-named in tissue extracts and the ash of plants.