A field experiment was conducted during the 2015 growing season from March to July to determine the N and P rates for optimum yield,
growth and quality of onion (Allium cepa L.), a factorial combination of two rates of N (0&50kg; ha-1) and two rates of P (0&75; kg ha-1) were
used for the experiment. Treatments were laid down in a Randomized Complete Block Design (RCBD) in a factorial combination with three
replications. The result of this study revealed that the application of nitrogen showed significant effects in most of studied characters while
P fertilization and the interaction effect N and P did not. Application of 50 kg N ha-1 increased plant height and leaf length by about 10.46 and
5.82%, respectively, over the check. Number of leaves increased by about 8.59% in response to the application of 50 kg N ha-1 over the control.
Leaf diameter and bulb length were not influenced by N fertilization. Phosphorus fertilization and its interaction with N did not significantly
affect onion plant height, leaves number and length. Application of 75kg ha-1 increased bulb length by about 22.28%, respectively, over the
control. Application of 50 kg N ha-1 increased the average bulb weight by 46.2%. The results of this experiment indicated that the application
of 50kgN per ha increased the total and marketable bulb yield about 46.2 and 60.4 % respectively over the control (1.43and 0.001t/ha
respectively).