Stonemeal is the application of crushed rocks in the soil. The objective of this work was to observe the action of microorganisms (inoculated and native) on the mineralization of basalt rock dust and to measure the elements released into the soil. This assessment was done by comparing decomposing particles of basalt powder applied to humic A horizon of a soil derived from granite. The basalt powder was collected at Cavinatto quarry, situated in Limeira-SP (Brazil). The experiment is being conducted in vitro, in isolated plastic containers with the following treatments: 1) soil; 2) sterilized soil; 3) soil without sterilization and with addition of inoculated microorganisms; 4) same as the first treatment plus basalt powder; 5) same as the second treatment plus basalt powder and 6) same as the third treatment plus basalt powder. The basalt powder was applied in a single dose of 4t/ha. The experimental units are maintained with 60% field capacity, and leached every 30 days. The leachate is collected and the elements Zn, Fe, Ca, Mg and K are determined. The results suggest that the treatments with basalt powder present greater release of most of the above mentioned nutrients. The treatments that have the inoculated microorganisms show greater nutrient solubilization when compared to either the sterile soil or to the treatment containing soil and native microbiota only. Thus, partial results indicate a tendency of nutrient levels to increase in solutions that contain basalt powder since the addition of inoculated microorganisms appears to stimulate this release. These results suggest that the combined use of rock dusts and microorganisms has the potential for commercial use in agricultural production systems.

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