Biosolubilization of verdete: An alternative potassium source for agriculture fertilizer

Potassium (K) is an essential nutrient for Brazilian agriculture, but about 95% of the potash fertilizer consumed in the country is imported. Some microorganisms are able to solubilize 'unavailable' forms of K-bearing minerals. Four potassium solubilizing bacteria (KSB) (Burkholderia sp., Bacillus sp., Caballeronia glathei and Paraburkholderia caribensis) were tested in two different culture media (Aleksandrov and Bushnell-Haas) with verdete rock in order to evaluate the potential of an alternative source of potassium fertilizer in bioleaching technology. Results showed that Burkholderia sp. and Bacillus sp. were able to release potassium from the rock in Aleksandrov medium. They increased the extraction by 71.3% and by 53.6%, respectively, in relation to control assays. Mixed culture (Burkholderia sp. + Bacillus sp.) improved K extraction by 47.1% above the control. On the other hand, Caballeronia glathei and Paraburkholderia caribensis did not present potassium extraction statistically different from their controls. These results have demonstrated the ability of two isolated bacteria to promote the solubilization of potassium from a Brazilian rock in a single batch assay and only by microbial action. Thus, these bacteria could be used for K-fertilizer manufacture with a great potential for application in Brazilian agriculture.