Plug plant fertilization and planting density affect onion productivity in Sicily.

The aim of this study was to evaluate the effects of different planting density and different levels of plug plant fertilization on onion production in Sicily. Onion landrace ‘Bisacquino’ was sown in the first week of January 2006 in a unheated greenhouse in polystyrene plug trays. Seedlings were fertigated with the following three different solutions containing (in mg l-1) 800 N - 400 P - 400 K, 1200 N - 600 P - 600 K or 1600 N- 800 P - 800 K. Trays were subirrigated with the nutrient solution both at one leaf stage and 10 days prior transplanting. Plug plants were field transplanted in the Sicilian hilly countryside. The plugs consisting of one, two, or three onion plants were set 20 cm apart in the row and transplanted as a cluster resulting in a plant density of 20, 40, or 60 plants-2. Higher fertilization levels positively influenced seedling growth in the greenhouse and resulted in higher yields and larger bulb weight. In addition, increasing planting density resulted in higher yields and in lower bulb weight.