Nitrogen-Saving Potential through the Application of Corrected Fertilisation Standards

A site specific nitrogen fertilisation requirement can be calculated with the help of the ‘corrected norms’ method. The method was applied and evaluated in the AgroCO₂ncept project in the Zurich Wine Country, where it demonstrated substantial nitrogen-saving potential.

Nitrogen (N-)fertilisation is responsible for around 18% of agricultural greenhouse-gas (GHG) emissions, thus representing the second-largest agricultural GHG source in Switzerland after livestock feed digestion (Agricultural Report 2023). A reduction in these emissions can be achieved by preventing N-surpluses, e.g. by calculating fertilisation requirements according to the ‘corrected norms’ (‘corrNorms’) method. Using correction factors (Fig. 1), the corrNorm adapts the N-fertilisation standards to the plot-specific soil, climate and cropping conditions, tailoring the amount of fertiliser to the crop’s requirements and thereby preventing N-surpluses (PRIF 2017). Scientific small-plot trials in Switzerland have already demonstrated that the corrNorm enables a reduction in N-fertilisation whilst maintaining steady yields.

As part of the AgroCO₂ncept project (2016–2021), the corrNorm was calculated retrospectively for 11 farms in the Zurich Wine Country over a four-year period (2018−2021) and compared with the N-fertilisation.

N-saving potential exists, but not in every case

Compared to the N-fertilisation standard, the corrNorm led to average N savings of around −14kg nitrogen per hectare across all 11 farms (Fig. 2). Owing to missing data from soil-sample analyses and field calendars, however, not all correction factors could be calculated for certain plots or years. This tended to lead to an underestimation of the potential N savings compared to the N-fertilisation standard.

Compared to the actual fertilisation practice of the farms, the fertilisation recommendations according to corrNorm led to an increase in the recommended quantity of N fertiliser of between +1.4 and +56.7kg nitrogen per hectare for certain farms in individual years (Fig. 3). The remaining farm years had N-saving potentials ranging between −7.6 and −75.1kg nitrogen per hectare, which, if implemented by eliminating mineral fertilisers, could lead to GHG savings of between −2.5t and −28.1t CO₂-equivalents per farm and year.

Farm-specific climate protection measures are key

The application of the corrNorm for the farms in the AgroCO₂ncept project has highlighted N-saving potential, and could thus contribute to a reduction in agricultural GHG emissions. However, the potential varies significantly according to farm and year, and in some cases the corrNorm could also indicate an increased fertiliser requirement. This underscores the importance of farm-specific climate protection measures.

It should be borne in mind, however, that the present results are based on a theoretical consideration where N-fertilisation recommendations according to corrNorm were not implemented and yield expectations were not reviewed. This means that the effects on yield and long-term soil fertility could not be examined. Looking ahead, an evaluation of the corrNorm in other agricultural contexts, such as e.g. in livestock-dense and grassland-focused regions, could provide further findings on the applicability and effectiveness of the corrNorm.