Yield-scaled mitigation of ammonia emission from N fertilization: the Spanish case

Synthetic nitrogen (N) fertilizer and field application of livestock manure are the major sources of ammonia (NH3) volatilization. This N loss may decrease crop productivity and subsequent deposition promotes environmental problems associated with soil acidification and eutrophication. Mitigation measures may have associated side effects such as decreased crop productivity (e. g. if N fertilizer application is reduced), or the release of other reactive N compounds (e. g. N2O emissions if manure is incorporated). Here, we present a novel methodology to provide an integrated assessment of the best strategies to abate NH3 from N applications to crops. Using scenario analyses, we assessed the potential of 11 mitigation measures to reduce NH3 volatilization while accounting for their side effects on crop productivity, N use efficiency (NUE) and N surplus (used as an indicator of potential N losses by denitrification/nitrification and NO3 -leaching/run-off). Spain, including its 48 provinces, was selected as a case study as it is the third major producer of agricultural goods in Europe, and also the European country with the highest increase in NH3 emissions from 1990 to 2011. Mitigation scenarios comprised of individual measures and combinations of strategies were evaluated at a country-and regional level. Compared to the reference situation of standard practices for the year 2008, implementation of the most effective region-specific mitigation strategy led to 63% NH3 mitigation at the country level. Implementation of a single strategy for all regions reduced NH3 by 57% at the highest. Strategies that involved combining mitigation measures produced the largest NH3 abatement in all cases, with an 80% reduction in some regions. Among the strategies analyzed, only suppression of urea application combined with manure incorporation and incorporation of N synthetic fertilizers other than urea showed a fully beneficial situation: yieldscaled NH3 emissions were reduced by 82%, N surplus was reduced by 9%, NUE was increased by 19% and yield was around 98% that of the reference situation. This study shows that the adoption of viable measures may provide an opportunity for countries like Spain to meet the international agreements on NH3 mitigation, while maintaining crop yields and increasing NUE.