A Field experiment was conducted to follow up the effect of-organic   and/or mineral N fertilizer either solely or in combinations on seed yield of common bean plant grown on sandy soil using ¹⁵N tracer technique. The experimental design was a Factorial Complete Randomized Block Design (FCRBD)   and treatments were replicated three times. Each experimental plot (10m2) received different proportions of organic and / or mineral N fertilizer up to 100% N in presence or absence of rhizobium inoculants. Results indicated the enhancement of seed yield and N uptake by bacterial inoculation. The overall averages of organic sources revealed the superiority of quite manure over leuceana residues followed by compost treatment.  Absolute values of Ndff, Ndfs+ Ndfo and Ndfa were frequently affected by portions of chemical and organic additives whereas Ndff tended to increase with increasing N fertilizer rate. Adversely, Ndfa was negatively affected by increasing N rate. Organic   additives enhanced the portions of Ndff and Ndfs+ Ndfo. This holds true with and without Rhizobium inoculation. These portions were markedly increased as affected by the addition of quite manure mixed with moderate N fertilizer rate (50% Chem-N + 50% quite manure-N). Low to moderate quantities of chemical fertilizer in combination with organic additives had enhanced the utilization of chemical-N source comparing to the full chemical fertilized plants.