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.