A field trial was conducted at Middle Egypt area (Sids Agric. Res. Station), Beni Suief Governorate (clay soils) for two successive summer seasons 2015/2016 using maize plant, variety (Th 310), to study the effect of partial substitution of mineral nitrogen fertilizer by farm composted (rice straw, corn stover and mixture of them) on soil fertility improvement, maize yields, its components and grains quality. Treatments comprised (100% mineral) recommended rates of N, P and K& (75% mineral-N + 25% rice straw) & (50% mineral-N + 50% rice straw) & (100% rice straw) & (75% mineral-N + 25% corn stover)& (50% mineral-N + 50% corn stover) & (100% corn stover) & 75% mineral-N + 25% (rice straw + corn stover) & 50% mineral-N + 50% (rice straw + corn stover) & 100 %
(rice straw + corn stover). The obtained results (average of two seasons) indicated that: *A slight decrease in soil salinity EC_e (dS m^-1) and soil pH, in the rhizosphere of grown maize after harvesting. In the other hand, soil organic matter was increased with farm composted and mineral-N fertilizer application. *Residual available soil N, P and K were increased with farm composted and mineral –N fertilizer application.* A significant increase in maize grain yield due to farm- composted and /or mineral-N fertilizer application. The highest values were (8.58 and 8.52 Mg ha^-1) which achieved upon treating with (75% mineral-N + 25% corn stover) treatment, then 75% mineral-N + 25% (rice straw + corn stover) treatment, respectively. *A significant increase in proteins%, P% and K % in maize grains yield. The highest value which reached to 10.37, 0.42 and 0.72, for Proteins%, P% and K %, respectively which achieved upon treating with (75% mineral-N + 25% corn stover) treatments, then 10.34, 0.40 and 0.70, for Proteins%, P %and K %, respectively, which achieved upon treating with (75% mineral –N + 25 (rice straw + corn stover((*These data already reflected on the proteins yields, P and K uptake .The highest value reached to 887, 36.03 and 61.77 (kg ha^-1) for proteins yields, P and K uptake, respectively. This achieved upon treating with (75% mineral -N+ 25% corn stover) treatments, then 884, 34.08 and 59.64 (kg ha^-1) for proteins yields, P and K uptake, respectively. This achieved upon treating with ((75% mineral-N + 25% (rice straw + corn)).