Decreasing NPK dose less than the recommended dose decreased significantly tuber yield [measured as tubers yield (g) per plant, tubers numbers per plant, tubers dry weight per plant and total yield (ton/fed.) as well as its components from protein, ascorbic acid ,starch, N, P ,K, total soluble solids and specific gravity in both studied seasons. In contrast, inoculation of any bacterial strains used induced significantly these parameters and the most effective treatments were found with NFB+PDB+SB followed with NFB+PDB and lastly with SB. The interaction treatments indicate that, plants received mixed three strains of used bacteria plus 50% or 75% NPK (from recommended dose) showed high values regarding yield and its components from crude protein and ascorbic acid , total soluble solids and specific gravity. The level of  75%NPK produced additive effects in this respect. NPK fertilizers at 50% only may be saved if potato tubers were inoculated with non-symbiotic fixing bacteria without serious effects on the tuber yield. Nitrate and nitrite concentrations were decreased significantly with decreasing mineral fertilizers dose in both seasons. Similarly, Nitrate and nitrite levels were decreased significantly when potato tubers inoculated with each of the bio-fertilizers used in comparession with those of uninoculated plants. Inoculation with either mixed strains of used bacteria or NFP+PDB gave the highest reduction in the levels of both nitrate and nitrite in potato tuber. Plants received 50% or 75% NPK (from recommended dose) produced the highest reduction in nitrate and nitrite levels compared with the control (100% recommended dose of NPK) while, the lowest reduction of both nitrate and nitrite were detected in tubers produced from plants inoculated with NFB. Decreasing NPK dose, overall bio-fertilizers used, decreased the percentages of reducing sugars, insoluble carbohydrates and total carbohydrates whereas increased non-reducing sugars and total sugars in potato tubers during the two growing seasons. Bio-fertilizers application alone significantly decreased  reducing sugars and total sugars whereas increased non-reducing sugars, insoluble carbohydrates and total carbohydrates percentages in the tubers of potato plants inoculated with each of the three bacterial strains used in comparison to those of uninoculated one. The most effective treatments was found with NFB+PDB+SB.Again, NFB strain was more effective than PDB followedwith SB. The interaction treatments, show that bio-fertilizers significantly decreased reducing sugars and total sugarswhereas increased non-reducing sugars, insoluble carbohydrates and total carbohydrates percentages in potato tubers of plants grown under any dose of NPK used in comparison to the corresponding control (uninoculated). Again, the best treatment was found with NFB+PDB+SB. Plants received only half the dose of the recommended NPK fertilizers together with the dual inoculation recorded considered increases in non-reducing sugars, insoluble carbohydrates and total carbohydrates in the tubers whereas, decreased that of reducing sugars and total sugars percentages. It could be concluded that the use of only bio-fertilizers for the production of potatoes is insufficient, so, they must be used together with mineral NPK fertilizers. Adding bio-fertilizers (naimly, Azospirillum brasilense , Psuedomonas fluerences and Bacillus circulance) to 50% of the mineral NPK fertilizers from the recommended dose (90 kg N + 37.5 kg P₂O₅ + 48 kg K₂O/fed.) exhibited resistance of potato grown against NPK  stress and induced its yield. The recommendation may reduce the extensive use of mineral fertilizers (about 50%) without affecting on potato productivity productivity. In addition the reduction of 50% from the  mineral NPK fertilizers used might help for reducing the production cost as well as diminishing the environmental pollution and minimizing the harmful effects of using chemical fertilizers on human health.