EFFECTS OF INTRA-ROW SPACING AND NITROGEN FERTILIZER LEVELS ON GROWTH AND YIELD OF ONION (ALLIUM CEPA L.) AT HUMBO WOREDA, SNNPR, ETHIOPIA

The productivity of onion crop is low due to poor agronomic and management practices in Humbo Woreda, Ampo Koysha Kebele. Therefore, a field experiment was conducted at Ampo Koysha Kebele during the cropping season of 2018/2019 to evaluate the effect of intra-row spacing and nitrogen fertilizer levels on growth and yield of onion. The treatments consisted of a combination of Four levels of intra-row spacing (5, 7.5, 10 and 12.5 cm) and four levels of nitrogen fertilizer, (0 , 23, 46 and 69 kg ha-1 ) which was laid out in factorial Randomized Complete Block Design (RCBD) with three replications. All growth and yield attributes were significantly affected by intra-row spacing and nitrogen fertilizer. The result showed that intra-row spacing and nitrogen fertilizer rates were highly significant (P<0.01) on days to maturity, plant height, leaf number, bulb diameter and dry matter yield. The tallest plant height (51.08 cm) and number of leaves per plant (9.78) were recorded from the wider spacing of 12.5 cm while the shortest plant height (45.48 cm) and number of leaves per plant (8.39) were recorded from the narrow spacing of 5 cm. Among the nitrogen rates tallest plant height (51.38 cm), number of leaves per plant (9.93) were recorded at 69 kg ha-1 , whereas the shortest plant height (44.66 cm) and number of leaves per plant (8.18) was recorded with the application of 0 kg N ha-1 . The interaction effect between intra-row spacing and nitrogen fertilizer rates was highly significant (P<0.01) on average bulb weight, marketable bulb yield, unmarketable bulb yield and total bulb yield. Marketable bulb yield and total bulb yield increased at higher plant population and increased nitrogen level. Thus using combination of nitrogen level of 69 kg ha-1 and 5 cm intra-row spacing was the best to get maximum marketable yield (30.58 t ha-1 ) and total bulb yield (31.92 t ha-1 ). In addition the highest net benefit 421,145 Birr was also obtained from this combination. However as the experiment was done for only one season and single location it has to be repeated by seasons and locations with consideration of additional varieties and soil type to make comprehensive conclusion and recommendation.