Growth, bulb yield and quality of onion ( Allium cepa L.) as influenced by nitrogen and phosphorus fertilization on vertisol I. growth attributes, biomass production and bulb yield

Abstract

A field experiment was undertaken to study the effect of different levels of nitrogen (N) and phosphorus (P) fertilizers on the growth, biomass yield and fresh bulb yield of onion (Allium cepa L.) grown on vertisol of Shewa Robit, North east Ethiopia. Five rates of N (0, 69, 92, 115, 138 kg ha-1) and five rates of P (0, 10, 20, 30, 40 kg ha-1) were arranged in a Randomized Complete Block Design replicated three times. Nitrogen showed significant effects in all of the parameters studied, while P fertilization and its interaction with N did not. The proportion of bolters per plot decreased by about 11 and 22% in response to the application of 69 and 92 kg N ha-1, respectively over the control. Regardless of the rate, N fertilization day extended days to physiological maturity by about 6 days over the control. Application of 69 kg N ha-1increased plant height and leaf length by about 10 and 11.5%, respectively over the unfertilized check. Number of leaves increased by about 8% in response to the application of 92 kg N ha-1 over the control. Leaf diameter and bulb length were not influenced by N fertilization. Regardless of the rate of application, N fertilization increased bulb diameter and average bulb weight by about 12 and 21.5%, respectively over the control. Application of 69 kg N ha-1 increased the development of splitted bulbs by about 45%, average bulb weight by 24%, total dry biomass by 20%, harvest index by about 4%, total bulb yield by 18%, and marketable bulb yield by 17% over the control. Application of 69 kg N ha-1 enhanced the growth of onion plant and resulted in optimum fresh total and marketable bulb yield on the vertisol of Shewa Robit, North east Ethiopia. The lack of significant response in onion to P fertilization could be attributed to the presence of adequate amounts of available P (16.02 ppm) in the soil and hence P fertilization for onion production is not advisable. Key words: Bulb diameter, bulb splitting, neck thickness, onion bolting, onion maturity.