A closer look at fertilizer legislations for silage maize across selected European countries: part II–overestimation of economically optimal nitrogen rates

Silage maize cultivation in Central Europe offers significant potential for improving nitrogen (N) efficiency, but quantifying N savings under current fertilization regulations and identifying further opportunities for improvement remain crucial. This study addresses these gaps by analyzing the influence of site-specific and management factors on the economically optimal N fertilization rate (EONR). EONR was calculated for 223 yield response functions across diverse silage maize cultivation conditions using a quadratic-plateau function, which outperformed quadratic and linear-plateau models in describing maize yield response to increasing N rates. A linear regression model was developed through a multistage analysis, incorporating only significant parameters available at the start of the growing season to estimate EONR. These EONRs, along with representative silage maize cultivation scenarios, were used to evaluate N fertilization recommendations within national frameworks. Key influences included management practices affecting plant residue quantity and carbon-to-nitrogen ratios, along with weather and soil parameters. Optimal management for silage maize following grain cereals, the predominant pre-crop in many regions, involved straw removal and frost-killed non-legume winter cover crops to maximize N saving potential. Official N fertilization recommendations exceeded calculated EONRs on average by more than 14%, with minimal correlation (R 2 < 0.1). In contrast, the developed regression model estimated EONR with a R adj 2 of 0.30, highlighting key research areas and opportunities for improving N efficiency in silage maize cultivation in Central Europe.