The present study was done in a pot experiment at Faculty of Agriculture, MonsouraUniversity during summer 2007  to study the combined effect of crop types, microbial inoculants and N fertilizer rates on availability and uptake of nitrogen at different days after planting (DAP). Randomized complete block design with three replicates was performed. The first factor was arranged for 3 crops i.e; rice (Oryza sativa) cv. Sakha 101, tomato (Lycopersicon esculentum., mill) cv. Super Merry Mand and cowpea (Vigna unguiculata L. Walp) cv. Karim seeds, The second factor (Microbial inoculants); (Non-inoculated – Inoculated with blue green algae) with the rice; non-inoculated – Inoculated with nitrobin for tomato crop and non-inoculated – inoculated with rhizobium for cowpea crop and the pollinating of the seeds before planting. Finally, the third factor was occupied with 3 nitrogen fertilizer rates (control, half and all recommended dose of N according recommended doses for  cultivated crops. The obtained results show as the following; -   Data illustrate that except 35 DAP for dry shoot and 70 and 105 DAP for dry root there are significant differences between average of dry shoots g pot^-1 at 70 and 105 DAP and as affected by affected by crop types i.e. (rice, cowpea and tomato crops), inoculations and N rates at different plant growth. -   Statistical analysis reveal that there are no significant differences between average of N concentration in shoots at 35and 105DAP except 70 DAP meanwhile, there are no significant differences between average of N concentrations % in  roots at 35 and 70 DAP except at 105 DAP as affected by crop types i.e.( rice, cowpea and tomato crops), inoculations and N rates at different plant growth. Generally, the highest mean values of dry shoot, roots and yield and N concentration (%) were obtained from all nitrogen dose + inoculated with Rhizobia + cowpea. Meanwhile, the lowest mean values of fresh shoots were obtained from untreated with nitrogen + untreated with inoculation + tomato.   -   It is evident that the highest mean values of utilization efficiency % of applied of nitrogen readings were attained due to all nitrogen doses + inoculated with Rhizobia + cowpea. On the other hand, the lowest means were obtained from half N doses + untreated with inoculation + rice.