How much can changes in the agro-food system reduce agricultural nitrogen losses to the environment? Example of a temperate-Mediterranean gradient.

Ammonia (NH3) volatilization, nitrous oxide (N2O) emissions, and nitrate (NO3-) leaching from agriculture cause severe environmental hazards. Research studies and mitigation strategies have mostly focused on one of these nitrogen (N) losses at a time, often without an integrated view of the agro-food system. Yet, at the regional scale, N2O, NH3, and NO3- loss patterns reflect the structure of the whole agro-food system. Here, we analyzed at the resolution of NUTS2 administrative European Union (EU) regions, N fluxes through the agro-food systems of a Temperate-Mediterranean gradient (France, Spain, and Portugal) experiencing contrasting climate and soil conditions. We assessed the atmospheric and hydrological N emissions from soils and livestock systems. Expressed per ha agricultural land, NH3 volatilization varied in the range 6.2-44.4 kg N ha-1 yr-1, N2O emission and NO3 leaching 0.3-4.9 kg N ha-1 yr-1 and 5.4-154 kg N ha-1 yr-1 respectively. Overall, lowest N2O emission was found in the Mediterranean regions, where NO3- leaching was greater. NH3 volatilization in both temperate and Mediterranean regions roughly follows the distribution of livestock density. We showed that these losses are also closely correlated with the level of fertilization intensity and agriculture system specialization into either stockless crop farming or intensive livestock farming in each region. Moreover, we explored two possible future scenarios at the 2050 horizon: (1) a scenario based on the prescriptions of the EU-Farm-to-Fork (F2F) strategy, with 25% of organic farming, 10% of land set aside for biodiversity, 20% reduction in N fertilizers, and no diet change; and (2) a hypothetical agro-ecological (AE) scenario with generalized organic farming, reconnection of crop and livestock farming, and a healthier human diet with an increase in the share of vegetal protein to 65% (i.e., the Mediterranean diet). Results showed that the AE scenario, owing to its profound reconfiguration of the entire agro-food system would have the potential for much greater reductions in NH3, N2O, and NO3- emissions, namely, 60-81% reduction, while the F2F scenario would only reach 24-35% reduction of N losses.