الفهرس 
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Abstract
The objective of this work was to study the biological weathering of potassium bearing minerals. Muscovite, orthoclase and vermiculite were chosen as k- bearing minerals. These minerals were inoculated to two strains of bacteria Bacillus megatherium (B1), Bacillus pasteurii (B2) and two species of fungi Penecillium expansum (F,) and Scopulariopsis brevicaulis (F2). The results indicated that Bacillus megatherium was
more effective in releasing potassium when orthoclase and vermiculite
were used as a source ofK. The highest amount ofK- released was after
24 hours incubation period while the lowest were recorded at the end of experiment (26 days). The content of potassium in mycelial mats ofF, was significantly higher than F2 with orthoclase and muscovite while F2 was more effective in releasing potassium from vermiculite than F2.
When muscovite or orthoclase was mixed with pure sand inoculation of Bacillus megatherium led to an increase in dry weight, K% and K-uptake of ryegrass and carrot.
However, inoculation of Bacillus megatherium in sandy soil resulted in a significant increase in all measured parameters (dry weight, K% and K-uptake). In calcareous soils, muscovite and orthoclase were more effective in releasing potassium to the plant roots rather than vermiculite. It was also noticed that percentage increase in dry weight, K% and K-uptake were more pronounced in ryegrass rather than those of carrot under the same treatments in calcareous soils.
Furthermore inoculating clay soils (to which K-bearing minerals were added) with Bacillus megatherium do not have any effect on the studied parameters.
Forms of bacterial inoculation also playing an important role in
the efficacy of the treatments. Adding bacterium strain in a suspension form was more effective in case of using muscovite and orthoclase to sandy soils than granules or powder forms. However powder forms were more effective in case of vermiculite than suspension or granules forms in the same soiL
In calcareous soils, preparation of Bacillus megatherium in suspension and powder forms has positive effect on all studied parameters with muscovite and orthoclase. Results also showed that the clay soils did not respond to any variation in forms of bacterial inoculation.