Onion is an important vegetable crop commercially grown both by large and small scale farmers in Ethiopia. Its production is highly dependent on availability of high and good quality seed, which is constrained by a number of problems including declining soil fertility and inappropriate fertilizer application. A study was conducted to investigate the effects of nitrogen (N) and phosphorus (P) fertilizer rates on onion seed yield and quality. The experiment was conducted at Kulumsa, South East Ethiopia, using four levels of N (0, 50,100 and 150 kg N ha-1) and four levels of P (0, 35, 70 and 105 kg P2O5 ha-1) fertilizers arranged in 4 × 4 factorial arrangements in randomized complete block design with three replications. The result of the study revealed that almost all of the yield and yield component parameters considered were significantly affected by the treatments. The crop phenology, growth and yield components were significantly influenced by the rate of N and P fertilizers and their interactions. More specifically, seed yield and seed quality were significantly (P<0.01) varied among treatment combinations. The combination of N at 100 kg N ha-1 and P at 70 kg P2O5 ha-1 gave the highest seed yield (1858.82 kg ha-1) with yield increment of about 57.72% over the control (no fertilizer application). As main factors each of N and P fertilizers at rates of 100 kg N ha-1 and 105 kg P2O5 ha-1 resulted in highest germination percentage of onion seed. Therefore, a combined application of N at 100 kg N ha-1 and P at 70 kg P2O5 ha-1 rates can be recommended for onion seed producers in the study area and areas of similar agro-ecology.
Key words: Soil fertility, commercial fertilizers, Alliaceae, Tri- super phosphate, Urea.
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