EFFECT OF INORGANIC NP FERTILIZERS AND VERMICOMPOST ON GROWTH, SEED YIELD, AND SEED QUALITY OF ONION (Allium cepa L.) AT MAITSEBRI, NORTHERN ETHIOPIA

Abstract

Onion (Allium cepa L.) is an important vegetable crop in Ethiopia. However, the yields of the bulb crop as well as seed are often constrained by low and imbalanced nutrient supply in soil particularly nitrogen and phosphorus. Therefore, a field experiment was conducted at the research station of Shire-Maitsebri Agricultural Research Center (SMARC), located in Tselemti Woreda to study the effect of inorganic NP fertilizers and vermicompost on growth, seed yield and seed quality of onion (Allium cepa L.) during 2016/17 dry season under irrigation. Bombay Red onion variety was used for the study. The treatments consisted of five NP fertilizer rates {0, 17.25 N: 23 P2O5 (25 %), 34.5 N: 46 P2O5 (50 %), 51.75 N: 69 P2O5 kg ha-1 (75 %) and 100 % of recommended NP rates (69 N: 92 P2O5 kg ha-1)} and four rates of vermicompost (0, 2.5, 5.0, 7.5 t ha-1). The experiment was laid out in a factorial arrangement using randomized complete block design (RCBD) with three replications. Data were collected on phenology and plant growth, seed yield, and seed quality. The results revealed that days to bolting, days to 50 % flowering, stand count percentage, number of umbels per plant, umbel diameter, number of seeds per umbel, seed weight per umbel and thousand seed weight were significantly affected by the main effect of NP fertilizer rates and vermicompost. Days to maturity was highly significantly influenced by the main effects of NP fertilizers (P<0.01) but, not significantly influenced by the main effect of vermicompost. The interaction effect of NP fertilizers and vermicompost had significant (P<0.05) effect on plant height. The highest seed yield per hectare (1462.5 kg ha-1) was obtained from the plants grown at 51.75 N: 69 P2O5 kg ha-1 with vermicompost at 2.5 t ha-1 which was about 263% higher than seed yield from unfertilized control plot. Purity seed test was significantly (P<0.05) improved by NP fertilizers and vermicompost. The interaction effect NP fertilizers and vermicompost also improved germination percentage, speed germination, seed vigour I and II. The highest net benefit (Birr 443693.5 ha-1) was recorded from application of 51.75 N: 69 P2O5 kg ha-1 with 2.5 t ha-1 vermicompost. It can, thus, be concluded that the combined application of 51.75 N: 69 P2O5 kg ha-1with vermicompost at 2.5 t ha-1can improve growth, yield, and quality of seed of Bombay Red onion variety in the study area.