In field experiment conducted in 2005-2007 the effect of a nitrogen source (ammonium nitrate, ammonium sulphate and ENTEC-26) in the amounts of 50, 100, 150, 100+50 kg N·ha-1 in onion (Allium cepa L.) Wolska cv. grown from sets for early cropping were estimated. Results of the experiment showed that ENTEC-26 was equally good source of nitrogen as ammonium nitrate and less efficient than ammonium sulphate. Split application of ammonium sulphate and ammonium nitrate produced higher while of ENTEC-26 similar yield of onion in comparison to a preplant single dose of fertilizer. Onion fertilized with ammonium nitrate and ammonium sulphate had only slightly higher content of vitamin C in bulbs and leaves than that fertilized with ENTEC-26. Plants of onion fertilized with ENTEC-26 contained also slightly higher level of reducing sugars in bulbs than by using the other source of N
