Asian Journal of Soil Science and Plant Nutrition

Onion productivity is strongly influenced by nitrogen management, particularly the timing and frequency of fertiliser application. Splitting urea applications may improve nitrogen availability during crop growth, thereby supporting bulb yield, quality, and nitrogen-use efficiency under field conditions. This study aimed to evaluate the effects of split urea application on onion yield, bulb quality, and partial factor productivity of nitrogen (PFPN) under Kassala conditions. Field experiments were conducted at Kassala and Gash Research Station Farm, Sudan, during the 2023/24 and 2024/25 seasons. Seedlings of the Baftaim S cultivar were raised in open-field nurseries for 7–8 weeks and transplanted in October. Five application frequencies, comprising two, three, four, five, and six splits of the recommended urea dose, were evaluated using a randomised complete block design. Total and marketable yields, bulb weight, bulb diameter, bulb dry matter, total soluble solids, and PFPN were assessed. Urea-splitting frequency significantly affected the measured yield and quality traits in both seasons. Six splits produced the highest total yields of 22.4 and 21.0 t ha⁻¹ and marketable yields of 22.0 and 20.0 t ha⁻¹ in 2023/24 and 2024/25, respectively. The same treatment recorded bulb weights of 163.0 and 159.0 g and bulb diameters of 8.4 and 7.0 cm. Bulb dry matter reached 19.0% and 21.0%, while total soluble solids reached 11.7% and 11.4%. PFPN also increased with increasing application frequency. Under the conditions of this study, splitting urea into six applications was associated with improved onion yield, selected bulb-quality attributes, and agronomic productivity of applied nitrogen compared with the two-split schedule.