Plant available potassium in rocks and mine tailings with biotite, nepheline and K‐feldspar as K‐bearing minerals

Crushed rocks and mine tailings with K‐feldspar, biotite and nepheline as their main K‐bearing minerals were tested as K‐fertilizers in a pot experiment with barley. Equal amounts of K (as analysed by X‐ray fluorescence spectrometry) were added to each treatment before the start of the experiment. Three successive sets of plants were grown for altogether 23 weeks without further addition of K. The K bound in K‐feldspar seemed to be nearly unavailable for the plants during the experimental period. However, considerable amounts of K were taken up from rocks and tailings containing nepheline and/or biotite as their main K‐bearing minerals. With further processing, some of these materials might be suitable as long‐term K‐fertilizers.