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Onion is one of the most important cash crops produced by smallholder farmers mainly during the irrigation season. However, the productivity of onion in Amhara Region is very low which is mainly associated with improper agronomic practices. This research was therefore conducted to increase the productivity of onion by identifying the optimum rate of nitrogen and intra-row spacing for economical production of the crop in Alawuha Small-Scale Irrigation Scheme. Four rates of nitrogen (0, 41, 82, 123 kg ha-1) and three intra-row spacing (6, 8, 10 cm) in factorial combination were laid out in Randomized Complete Block Design with three replications. Results indicated that nitrogen and intra-row spacing significantly influenced most of the growth and phenological parameters of onion where application of 123 kg ha-1 nitrogen increased leaf number by 67.3% and prolonged days to maturity of onion by about 7 days compared to the respective control plants. Similarly, nitrogen rate and intra-row spacing significantly affected bulb yield of onion where the highest marketable bulb yield (37.48 t ha-1) was recorded by application of 123 kg ha-1 on plants spaced at 6 cm intra-row spacing which was statistically similar with those yield (35.07 t ha-1) recorded with the combination of 82 kg ha -1 nitrogen and 6 cm intra-row spacing. Application of 123 kg ha-1 nitrogen on plants spaced at 6 cm intra-row spacing is recommended for production of onion in Alawuha Small-Scale Irrigation Scheme as it recorded the highest net benefit (Eth-Birr 429,569) with relatively high marginal rate of return.
Allium cepa L., Bombay red, Bulb yield, Spacing, Vegetative growth.