Waste silicate minerals as potassium sources: a greenhouse study on spring barley

After 1989, the use of potassium (K) mineral fertilizers in the Czech Republic dropped from ～55 kg K ha^?1 to a mean rate of ～6.5 kg in the last decade. In order to test alternative solutions for K fertilization, the trioctahedral mica mineral zinnwaldite (8% K), orthoclase (10% K) and waste mica from Cínovec (Kru?né Hory Mts/Erzgebirge, Czech Republic), consisting primarily of zinnwaldite, were applied as the only K sources for spring barley. The minerals were treated in three different types of high-energy mills under different working conditions. Application rates in the range 139–820 mg K kg^?1 were tested in quartz sand cultures. In all treatments, plant growth, total plant biomass and the K content in the plant tissues increased in the order zinnwaldite > waste mica > orthoclase. K fractionation and K plant uptake were significantly influenced by the milling method used. The effect of 195 mg K kg^?1 as zinnwaldite on K uptake from K-depleted soils was positive; however, it was smaller than in sand cultures because of the relatively high content of non-exchangeable K in the soils. Direct use of waste mica as a K fertilizer is limited by the increased fluorine and heavy metal content.