Influence of Plant Density and NPK 15:15:15 Fertilizer on Some Agronomic Characters and Proximate Composition of Onion (Allium cepa L.) in Edo Rainforest of Nigeria

The effect of plant population density and varying levels of NPK 15:15:15 fertilizer on the growth, yield and proximate composition of onion (Allium cepa L.) was investigated in a 2-year study, 2010/2011 and 2011/2012. The experiment was a factorial combination of three plant densities 333,333, 250,000 and 160,000 plants ha-1 and four levels of NPK 15:15:15 inorganic fertilizer at 0, 40, 80 and 120 kg /ha NPK laid out as a randomized complete block design with three replications. Results indicated that the three plant densities of 333,333, 250,000 and 160,000 plants ha-1 were statistically similar in both trials and enhanced the growth of onion in terms of stem diameter except at 6 weeks after transplanting (WAT). This trend was also observed for proximate composition of onion leaves and bulbs and number of leaves in 2010/2011. In 2011/2012, the lowest plant density of 160,000 plants/ha produced more leaves compared to the higher plant populations of 333,333 and 250,000 plants/ha. Chlorophyll content, CGR and bulb length were similar at the lower densities and significantly higher than those produced at the highest plant density of 333,333. In both trials bulb yield was significantly similar at densities of 333,333 and 250,000 plants/ha. Increase in fertilizer application significantly increased the moisture content. Crude protein and crude fiber but decreased the percentage dry matter content of leaves and bulbs. However, optimum bulb yield was obtained at density of 250,000 plant/ha with fertilizer application rate of 80 kg/ha NPK 15:15:15.