الفهرس 
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Abstract
Two field experiments were carried out at the Agriculture Experimental Station, Faculty of Agriculture, Mansoura University, Mansoura Egypt during the two successive growing seasons of 2001/2002 and 2002/2003 aiming to study to what extent the bio-fertilizers can replace the recommended NPK mineral fertilizers on potato plants Spunta cv. without affecting on its productivity. Different rates of the recommended NPK mineral fertilizers and three strains of non-symbiotic bacteria as a bio-fertilizers sources; Azospirillum brasilense as nitrogen-fixing bacteria (NFB), Paseudomonus fleuressenec as phosphate-dissolving bacteria (PDB), as well as Bacillus circulans as silicate bacteria (SB) were examined for potato growth and its productivity. Certain morphological and physiological aspects were estimated. Tubers yield and their quality were evaluated. 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 vigorous potato growth and induced most of the plant growth parameters studied and improved the chemical constituents of potato which in turn might be positively reflected on potato yield. Such enhancement might be related to the improvement effects of bio-fertilizers on physical and biological properties of the soil which promotes the release of some nutrient and/or some growth substances in rooting zone for readily available forms which consequently might increase their uptake by plants. Therefore, the application of bio-fertilizers (Azospirillum brasilense , Psuedomonas fluerences and Bacillus circulance) in combination with 50% NPK from the recommended dose is recommended for improving growth, yield with good quality and some chemical constituents which are responsible for potato yied. 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.