Influence of plant density and phosphorus levels on the growth and yield of onion (<i>Allium cepa</i> L) in humid ultisols

Abstract

Field study was conducted at the Experimental Farm of the Faculty of Agriculture, University of Benin, Benin City, Nigeria in 2015 and 2016 to determine the effect of plant density and phosphorus application on the growth and yield of onion in the humid ultisols environment of Benin City. The experiment was laid out in a 3 x 3 split plot design with three replications. The main treatments were three plant densities 50 (10 x 20 cm), 66 (10 x 15 cm) and 100 (10 x 10 cm) plants m-2 and sub-treatments were three levels of phosphorus fertilizer (0, 30 (68.71 kg P₂O₅) and 60 (137.42 kg P₂O₅) kg P ha^-1). Data were collected on plant height and number of leaves per plant during the vegetative phase, while, at harvest, data were collected on number of roots, roots length, bulb length, bulb girth, bulb weight, bulb yield, relative yield (RY) and phosphorus use efficiency (PUE). Significant effect of plant density was observed on relative yield and PUE only. Phosphorus application significantly influenced all the parameters measured. The highest bulb yield (17 t ha^-1) was at 60 kg P ha^-1 which was comparable to 15 t ha^-1 observed at 30 kg P ha^-1. Onion bulb yield was significantly and positively correlated with plant height (r =0.813) and number of leaves per plant (r = 0.827). Based on the relative yield and PUE, a plant density of 50 plant m^-2 and 30 kg P ha^-1 are therefore recommended for onion cultivation in the humid ultisols environment of Benin City.