Lovro Sinkovič Agricultural Institute of Slovenia, Crop Science Department, Ljubljana, Slovenia

Mojca Škof Agricultural Institute of Slovenia, Crop Science Department, Ljubljana, Slovenia

Kristina Ugrinović Agricultural Institute of Slovenia, Crop Science Department, Ljubljana, Slovenia

Onion is one of the most important vegetable bulb crops in the world. A field experiment was carried out at the experimental fields of the Agricultural Institute of Slovenia in 2017 with the aim to examine the effect of three nitrogen (N) fertilization rates on the physico-chemical characteristics of bulbs of five onion varieties. Three autochthonous and two hybrid onion varieties were evaluated. During the growth 0, 162 and 324 kg Nha-1 were applied. The number of fleshy scale leaves, bulb weight, height, diameter and firmness were determined on onion bulbs. In addition, the total soluble solids and total sugars were analysed. Both factors, i.e. variety and N fertilization rate, significantly affected the number of fleshy scale leaves, while N fertilisation rate also affected bulb firmness and the variety influenced the content of total soluble solids and bulb height. Hybrid varieties had lower total soluble solids compared to autochthonous varieties.