Nitrogen Fertilization for Silage Maize: N Rates, Organic Inputs, and Livestock Integration
Silage maize is grown on over 2 million hectares in Germany — it is the largest single arable crop by area, driven by demand from dairy and biogas farms. Its nitrogen management is deeply intertwined with livestock manure and digestate applications, making it one of the most DüV-contested crops and the one most frequently implicated in nutrient balance exceedances.
Nitrogen Demand and N Removal
Germany's average silage maize yield is around 46 t fresh weight per hectare at ~32% DM (Herrmann & Taube 2004, 2005). At full crop removal (whole plant), silage maize removes approximately 4.0 kg N per tonne FM from the field (PDA Leaflet 17), meaning a 46 t/ha crop removes ~184 kg N/ha in total. Advisory references for Germany commonly cite around 180 kg N/ha at reference yield for silage maize; current official DBE Bedarfswerte in several states are higher. The figures in this article are agronomic guidance; always verify with the applicable current state DBE table. The nitrogen response shows strong returns up to 85 kg N/ha and diminishing but still significant returns from 85–170 kg N/ha.
Organic N: The Central Planning Variable
Silage maize farms almost always apply livestock slurry or biogas digestate before or during the growing season. Under DüV 2020:
- The 170 kg organic N/ha farm average limit applies
- Slurry ammonium-N availability for maize: typically 60–70%
- Digestate (liquid fraction): typically 70–80% availability
These availability factors must be used to calculate the effective mineral equivalent of organic applications, then subtracted from the total planned dose.
Example: 40 m³ cattle slurry/ha with 3 kg total N/m³ = 120 kg N/ha total. At 65% availability = 78 kg effective N. If the crop needs 180 kg and Nmin provides 30 kg, then 180 − 30 − 78 = 72 kg/ha mineral N still needed.
Application Strategy
- Organic N (slurry/digestate): applied before incorporation, autumn (limited) or spring before sowing
- Starter mineral N (at sowing or BBCH 12–16): side-band or row placement, 60–100 kg N/ha
- Optional top-dress (BBCH 16–30): only if organic N was insufficient
DüV Compliance Points
Silage maize is the crop most scrutinized in nutrient balance audits. Farms with intensive dairy operations must carefully track the farm-level organic N balance across all fields. Exceeding the 170 kg org N/ha limit is a DüV violation regardless of effectiveness.
Conclusion
For silage maize, the N calculation is primarily an organic-plus-mineral budgeting exercise. Accurate documentation of all organic applications is both a regulatory requirement and a prerequisite for accurate economic N optimization.
Calculate your silage maize N rate including organic inputs: Open the NRate Calculator