Iron oxide (Pigment Black 11) is a intense black non toxic and very cheap pigment. I think I have read somewhere that soil from shops is sometimes pigmented with iron oxide because it sells better. But I could not find a reference any more.
Some plants need different soil (some with more and less humus content) in my garden and the surface looks very blotchy at the moment and I wonder
what are the long term effects of iron oxide pigments in soil?
- Will plants absorb the pigment and get darker too?
- Will it react with rain or natural fertiliser?
- Where can I find studies on the consequences of iron oxide pigments on the nutritiousness of vegetables and fruits?
According to instinct I expect nothing good from pigments in soil, but I could not find a reliable statement. Please support your answer with references.