Growth, Yield, and Quality of Onion (Allium cepa L.) as Influenced by Intra-Row Spacing and Nitrogen Fertilizer Levels in Central Zone of Tigray, Northern Ethiopia

Research Paper (postgraduate) from the year 2018 in the subject Agrarian Studies, grade: Degree of MASTER, Jimma University College of Agriculture and Veterinary Medicine (Jimma University), course: Horticulture, language: English, abstract: Haphazard and inappropriate plant spacing and poor soil fertility management practices are among the major factors constraining onion production in the Central Zone of Tigray. Therefore, a field experiment was conducted in Axum district from October to March 2014 to assess the influence of intra-row spacing (2.5, 5, 7.5, 10 and 12.5 cm) and nitrogen rate (0, 41, 82 and 123 kg N ha-1) on growth, bulb yield, and quality of onion. The experiment was laid out in a randomized complete block design (RCBD) of factorial arrangement with three replications. The main effects of nitrogen rate and intra-row spacing influenced only the plant height and stand count significantly (P < 0.01). The tallest plants (46.70 cm) were obtained from plants treated with 82 kg N ha-1 as well as those spaced at 7.5 cm intra-row spacing (43.78 cm). The highest stand count (90.33%) at harvest was recorded from plots that received 82 kg N ha-1 and spaced at 12.5 cm (98.04%). Nitrogen rate and intra-row spacing interacted to significantly (P < 0.01) to influence all parameters. Thus, increasing the rate of nitrogen across the increasing intra-row spacing significantly prolonged days to maturity, enhanced average bulb weight, bulb diameter, bulb neck diameter, leaf number per plant, leaf diameter, shoot dry matter, and dry total biomass yield. In general, the highest values of these parameters (126.67, 123.85 g, 6.05 cm, 1.35 cm, 12.57, 1.38 cm, 3.22 g and 13.08 g, respectively) were attained in response to the application of 123 kg N ha-1 and 12.5 cm intra-row spacing. However, their least values (100, 23.99 g, 2.33 cm, 0.68 g, 6.60, 0.47 cm, 0.73 g, and 2.72 g, respectively) were obtained at 0 kg N ha-1 and 2.5 cm intra-row spacing. The highest value of bolting (31.95%) was observed from the application of 0 kg N ha-1 and plant spacing of 2.5 cm. Increasing the N rate across the increasing intra-row spacing increased the yields of over-sized bulbs whereas decreasing the yields of small-sized, under-sized bulbs and unmarketable bulb yield. The highest yield of over-sized bulbs (4.03 t ha-1) was recorded at 123 kg N ha-1 and the intra-row spacing of 12.5 cm.