Two field experiments were carried out at a private farm (Kafr Alam, Meniat el-Nasr), Dakahlia Governorate, during winter seasons of 2008/09 and 2009/10, to study the effect of different sources of nitrogen fertilization, i.e., ammonium nitrate (AN), ammonium sulphate (AS) and urea (U) as soluble form of nitrogen with or without nitrification inhibitors dicyandiamide (DCD) as well as ureaform (UF), sulpher coated urea (SCU), isobutylidene diurea (IBDU) , polyolefin-coated urea (PCU) and compost as slow-release N-sources on productivity and quality of potato cv. Diamant. The obtained results revealed that N-sources differed significantly in all studied characters. Application of PCU had more plant height, fresh and dry weights per plant, total tuber yield and marketable yield, followed by IBDU in both seasons. Moreover, PCU and IBDU had significant higher dry matter, specific gravity, NPK-uptake, and starch content in comparison with other treatments. Meanwhile, application in urea as a soluble form gave the highest reducing sugars compared with other treatments. On the other hand, nitrate and nitrite content of potato tubers in treatment amended with AN at 180 kg fed^-1 was higher than with other treatments in the two seasons. This study suggests that slow release N fertilizers, e.g., polyolefin-coated urea and isobutylidene diurea at 135 kg N fed^-1 are the most effective treatments for high productivity, quality and net profit of potato fields with keeping the health and safety of human and environment.