The field experiment was carried out during two experimental seasons of 2005/2006 and 2006 / 2007 under calcareous soil and rainfall conditions in El-Hammam region at North Western Coastal Zone (NWCZ) of Egypt. The aim of this research was to study the vegetative growth,  yield and its components as well as chemical compositions of onion plants (Allium cepa, L.) cv. Giza-20 as influenced by 4 treatments of supplementary irrigation  (rainfall, rainfall plus 60 mm/fed, rainfall plus 75 mm/fed and rainfall plus 90 mm/fed) and 4 foliar spray treatments (potassium carrying phosphor (K.P), potassium carrying nitrogen (K.N), (K.P plus K.N) and control treatment. The  commercial name were Butasin – p and Butasin – N and its interaction. The concentration of each foliar spray treatment was 4 cm \ L. Application of foliar spraying was three times at 30, 45 and 60 days after transplanting.  Rainfall plus 90 mm supplementary irrigation treatment led to obtain the maximum values for all vegetative growth characteristics (survival ratio, plant length, number of leaves per plant, fresh and dry weight per plant. The values of yield, (bulb fresh and dry weight, bulb dry matter%, bulbing ratio and yield ton/fed were increased by increasing the rate of supplementary irrigation. Also, the bulb content of T.S.S., nitrogen, phosphorus and potassium, gave the highest values  with using rainfall plus 90 mm/fed supplementary irrigation. Foliar spray treatment with K.P + K.N, gave the highest significant increases when compared with other foliar spray treatments on all characteristics under study,  The interaction treatment, rainfall and 90 mm supplementary irrigation combined with foliar spray treatment with K.P + K.N, led to obtain the maximum values for all characteristics under study in both growing seasons.