Bulb Development in Onion (Allium cepa L.) I. Effects of Plant Density and Sowing Date in Field Conditions

Early and later maturing cultivars of both spring- and autumn-sownonions were sown on two dates at 25, 100 and400 plants m^–2.High levels of nutrients and irrigation were applied. Both high plant density and early sowing advanced the date atwhich bulb scales, rather than leaf blades, were initiated atthe shoot apex and so advanced the date of maturity by up to46 d. The later maturing spring-sown cultivar showed greaterresponses to density and sowing date than the earlier maturingspring-sown cultivar which in turn was more responsive thanthe autumn-sown cultivars. For each cultivar, maturity date increased linearly with decreasesin the percentage radiation intercepted by the leaf canopy. Onion, Allium cepa L., bulbing, competition, spacing