Potassium is one of the three essential elements viz., NPK needed in large quantities for the growth and reproduction of the plants and it plays many vital roles in plant nutrition. The crop production in Egypt relies completely on imports to meet its annual requirement of potash fertilizers besides; the high cost of conventional, water soluble K fertilizers constrain their use by most of the farmers in the country. In order to reduce the dependence on imported potash, feldspar a potash mineral, contains 10.5 % K2O and therefore it could be a potential K-source for crop production. Novel approaches are needed to unlock K from the silicate structure of this mineral in order to render K more available for plant nutrition. A strain of silicate dissolving bacteria (Bacillus circulans) as well as fungus (Penicillium sp.) were used as bio-inoculants. These studies were undertaken to evaluate the effectiveness of bacterial and fungus inoculation in combination with two levels of feldspar and mineral potassium fertilizer (full recommended dose and half recommended dose) on K-releasing capacity as well as potato yield. To achieve this target, bio-inoculated potato tubers (Solanum tuberosum, L.) were sown on calcareous soil at Nubaria Agriculture Research Station. The obtained data showed that inoculation with silicate dissolving bacteria as biofertilizer in the presence of different potassium sources increased all examined potato tuber yield, tuber content of carbohydrate and protein, moreover soil available and plant (shoot and tubers) content of N, P , K ,Fe, Mn, Zn and Cu compared to the sole use of K sources. On the other hand, the highest tubers yield ( 15.62 and 15.33 ton fed.-1) were obtained when mineral fertilizer and feldspar were inoculated with bacteria. The apparent nutrient recovery and partial factor productivity were significantly enhanced by inoculated feldspar with Silicate Dissolving Bacteria (SDB) than other treatments. However, the use of feldspar in combination with biofertilizers may be more useful and economically.