Abstract:
Use of optimum nitrogen rate and improved onion varieties are important practice in onion
production. However, onion growers in West Demmbia District often used undefined amount
of nitrogen rate and local varieties, which contributes low yield. Therefore, a field experiment
was conducted from December 2018 to May 2019 in Dembia District to improve productivity,
and quality of onion using optimum nitrogen rates and improved varieties. The treatment
consisted of a factorial combination of six levels of nitrogen rates (0, 46, 69, 92, 115 and 138
kg N ha
-1
) and two improved varieties (Adama Red and Bombay Red). The experiment was
laid out in a randomized complete block design with three replications. All collected data
were analyzed using SAS software. The interaction effects of nitrogen rates and varieties had
not significant in all parameters. The main effect of nitrogen rates and varieties had not
significant effect on plant height, leaf length, number of leaf per plant and leaf diameter at 30
days after transplanting. However, there were significant differences in plant height, leaf
length and leaf diameter at 60 and 90 days after transplanting. In addition, nitrogen rates
showed significant effect in days to physiological maturity and all yield related parameters.
Adama Red variety gave higher marketable bulb yield (15.56 t ha
-1
) as compared to Bombay
Red (13.89 t ha
-1
). Increasing nitrogen rates from 0 to 138 kg ha
-1
increased all growth and
yield related parameters. The highest marketable bulb yield (19.23 t ha
-1
) was obtained at the
rate of 138 kg N ha
-1
followed by 115 kg N ha
-1
(17.38 t ha
-1
).
1
On the other hand, 138 kg N ha
decreased the quality of onion. Because the maximum rate of nitrogen increased neck
diameter, decreased dry matter content and total soluble solids). The highest percentage of
sprouted, rotten and weight lost bulbs were observed with the application of 138 kg N ha
.
Marketable and total bulb yield were very highly significant (P < 0.001) and positively
correlated with the number of leaf per plant, leaf diameter, fresh and dry weight of
aboveground biomass, days to physiological maturity, average bulb weight, bulb diameter
and bulb length. Treatment combination Adama Red and 138 kg N ha
-1
gave the highest net
benefit (303,241ETB ha
-1
) with the marginal rate of return of 4392.76%, which is greater
than the minimum requirement (100%). On the other hand, the lowest net benefit (137,744.4
ETB ha
-1
) was obtained from treatment combination Bombay Red and 0 kg N ha
. Therefore,
Application of 138 kg N ha
-1
for Adama Red variety is the best recommendation in the
study
area. To make conclusive recommendation the experiment should be repeated over season
and across locations by using additional varieties and nitrogen rates higher than 138 kg N
ha
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