Abstract: A field experiment was carried out during two successive summer seasons of 2010 and 2011 at Moshtohor Experimental Farm, Faculty of Agriculture, Benha University, Qalubiya Governorate to investigate the effect of applied different sources from potassium fertilizers (potassium sulphate as chemical fertilizer and feldspar as natural rock potassium) at the recommended rate( 48 kg K2O/fed) either single or in combination with others and/or the biofertilizer (silicate dissolving bacteria ,SDB) i.e. Bacillus circulans on plant growth and chemical composition, yield and its components as well as tuber roots quality of sweet potato (Ipomoea batatas (L.) Lam.) cv. Minufia 6. Obtained results indicated that, using the treatment 50% potassium sulphate + 50% K- feldspare + SDB recorded maximum values of plant fresh and dry weight, chlorophyll a, total chlorophyll (a+b), percentage of N and K in vine, as well as increased roots tuber yield and its components, i.e. average of root tuber fresh weight, yield of tubers/ plant and total yield /fed. In addition, it improved the quality of tuber roots, i.e. P, K, reducing, non-reducing, total sugars and carbohydrates percentage as well as dry matter content compared to the other tested treatments. From the forgoing results, it can be recommended to apply sweet potato plants by 50% potassium sulphate + 50% K-Feldspar + SDB to obtain maximum values of most studied variables. From the economic point, it may be a way to reducing the cost production by replacing partly the expensive potassium chemical fertilizer by the chipper locally available feldspar mineral in combination with silicate dissolving bacteria . Key words: Sweet potato, K-feldspar, Potassium sulphate, Bacillus circulans.