Nitrogen Fertilization for Onions: 155–210 kg/ha DüV Range and Three-Split Timing
Onions (Speisezwiebeln, Allium cepa) are a high-value vegetable crop in Germany, particularly important in Lower Saxony, Rhineland-Palatinate, and Baden-Württemberg. With typical yields of around 45.7 t FW/ha (Destatis 2025) and a DüV N demand range of 155–210 kg N/ha depending on yield potential, onions have one of the highest nitrogen budgets of any German vegetable crop — matched by precise split requirements and a strict application stop date.
Nitrogen Demand
DüV 2020 Anlage 4 Tabelle 4 establishes a yield-dependent N demand for dry bulb onions (Trockenzwiebeln) of 155–210 kg N/ha. Note that official tables distinguish between dry bulb onions (Trockenzwiebeln) and bunch/spring onions (Bundzwiebeln), which carry a lower N demand — this article focuses on dry bulb production. At the Destatis 2025 average of 45.7 t/ha, the applicable Bedarfswert falls in the upper range of this scale. Each 5 t/ha yield difference adjusts the N demand accordingly.
The yield-dependent scaling reflects onion's strong positive N response: LWK Niedersachsen's Düngebedarfsermittlung Zwiebeln documents a clear relationship between N supply and both bulb size and total fresh weight yield, provided N is available during the critical bulb enlargement phase.
Three-Split Application with Hard Stop at BBCH 42
LWK Niedersachsen recommends a three-split N strategy timed to crop development:
- First application (at/near sowing, or transplanting): 50–70 kg N/ha — supports early establishment
- Second application (6th cultural week — Nmin trigger):* 60–80 kg N/ha — main growth phase
- Third application (BBCH 31–39): 40–60 kg N/ha — late vegetative push before bulbing
Hard stop: BBCH 42 (early bulbing, ~10 mm bulb diameter). No nitrogen after this stage under any circumstances — late N delays bulb ripening, increases disease susceptibility (Botrytis, neck rot), and can cause double bulbing which destroys commercial value.
*The Nmin trigger: LWK Niedersachsen notes that the second application should be timed around the 6th cultural week and adjusted based on a mid-season Nmin re-sampling to avoid over-application on high-N fields.
Nmin Accounting is Critical
The Nmin sampling for onions is recommended before sowing (standard 0–60 cm). Given the high DüV N range, the difference between a high Nmin site and a low one can be 40–60 kg N/ha — this directly determines whether the first split is full-sized or halved.
Quality Implications
Excess sulfate and nitrogen content in onions affects storage life and odor characteristics. Sulfur co-application at 20–30 kg S/ha is standard practice (like with rapeseed), as S deficiency prevents efficient N utilization in Allium species.
Conclusion
Onion nitrogen management combines a high total N budget with highly precise timing constraints. The hard stop at BBCH 42 is non-negotiable, and mid-season Nmin re-sampling is best practice on variable-N fields.
Calculate your onion N rate with yield-adjusted DüV requirements: Open the NRate Calculator