Reconciling food production and environmental boundaries for nitrogen in the European Union

Meeting European policy targets for reducing nitrogen (N) pollution while maintaining crop production is a large challenge. Strategies to tackle this dual challenge should assess where reducing N losses is most needed while accounting for variation in agricultural systems and ecosystems' vulnerability to N loading. We used a spatially explicit N balance model (INTEGRATOR) to assess whether crop production targets and thresholds for N impacts on biodiversity and water quality in the EU can be reconciled by (i) redistributing N inputs from excess regions to regions where environmental thresholds are not exceeded and (ii) improving N management to reduce ammonia (NH₃) emissions from manure and enhance field-level N use efficiency (NUE). At current NUE, reducing N inputs to comply with three environmental thresholds (critical N deposition on terrestrial ecosystems and critical N concentrations in surface water and groundwater) would reduce European crop production by 50%. The widespread exceedance of thresholds does not provide much room for redistribution: increasing inputs to close yield gaps on land where N thresholds are not exceeded can only increase crop production by 3%. To achieve surface water quality targets without crop production losses, average NUE needs to increase from 0.64 to 0.78, whereas achieving groundwater targets only requires a modest increase from 0.64 to 0.67. In hotspot areas, however, crop production and N thresholds can only be reconciled at NUEs of >0.90, which is not feasible. Reducing manure NH₃ emission fractions to 0.10 by adopting best-management practices reconciles current crop production and thresholds for agricultural NH₃ emission (in view of critical deposition) on only half of the agricultural area. In some regions, technologically feasible improvements in N management are thus insufficient to both maintain current crop production and respect environmental boundaries. Overall, the evaluated measures could reconcile ~80% of current EU crop production with N thresholds.