Geographic Variation in Nitrogen Budgets in Agricultural and other Terrestrial Ecosystems over Europe

Nitrogen (N) budgets of agricultural systems give important information for assessing the impact of N inputs on the environment, and identify levers for action. N budgets of agro-ecosystems in the 27 EU countries are established for the year 2000, considering N inputs by fertiliser application, manure excretion, atmospheric deposition and crop fi xation, and N outputs by plant uptake, gaseous emissions, mineralisation, leaching and runoff. Country N budgets for agro-ecosystems are based on the models INTEGRATOR, IDEAg, MITERRA and IMAGE. Fine geographic distribution is depicted with the former two models, which have higher spatial resolution. INTEGRATOR is the only available model for calculating non-agricultural terrestrial N budgets systems. For EU-27, the models estimate a comparable total N input in European agriculture, i.e. 23.3–25.7 Mton N yr− 1 , but N uptake varies largely from 11.3–15.4 Mton N yr−1 , leading to total N surpluses varying from 10.4–13.2 Mton N yr −1 . Despite this variation, the overall diff erence at EU-27 is small for the emissions of NH 3 (2.8–3.1 Mton N yr −1 ) and N2O (0.33–0.43 Mton N yr−1) but estimates vary largely at a regional scale. Th e estimated sum of N leaching and runoff at EU-27 is roughly equal to the sum of NH3 , N2O and NOx emissions to the atmosphere, but estimates vary by a factor two, from 2.7 to 6.3 Mton N yr −1 . Trends in N fl uxes in agro-ecosystems since 1970 show an increase in N inputs by fertilisers and manure up to 1985, followed by a decrease since 1985 in response to a decrease in crop production and in animal numbers. Actually, livestock decreased since 1970, but in the period 1970–1985 the N input by manure excretion still increased due to an increase in N excretion rates. In non-agricultural system (forests and semi-natural vegetation), the estimated total N input is near 3.2 Mton N yr −1 , while the net N uptake is near 1.1 Mton N yr −1 , leading to a surplus near 2.1 Mton N yr −1 . Compared to agricultural systems, the estimated N fl uxes in non-agricultural systems are about fi ve times lower for N 2 O emissions and 10 times lower for NO x and NH 3 emissions and for the sum of N leaching and runoff. The largest uncertainties in fl ux values, as estimated from inter-model comparison, concerns N leaching and runoff , followed by N2O emissions, from agricultural ecosystems. Recommendations: • Future research should focus on reducing the fl uxes with the most uncertainty (N leaching and runoff , followed by N 2 O emissions, from agricultural ecosystems), including studies on denitrifi cation. • To improve model assessments and enable model validation, databases should be set up of: (i) N contents in major crops/vegetation in various regions (to improve estimates of N uptake and N surplus), (ii) NH 3 and N 2 O emissions based on inverse modelling approaches

JRC.DDG.H.2 - Climate change and air quality