Quantification and comparison of subnational and national agricultural nitrogen flows in Denmark and Sweden

Abstract Ensuring food production with low nitrogen (N) environmental emissions requires good quantitative knowledge of N flows in agricultural systems to monitor emissions and N use efficiency (NUE, the ratio of N outputs to inputs). Our study quantifies the main N agricultural flows at subnational and national scales in Denmark and Sweden from 2011 to 2020, calculating the NUE for crop and livestock production and associated nitrous oxide (N 2 O) and ammonia (NH 3 ) emissions. In Denmark, our results indicate a similar use of organic (manure) and synthetic N fertilizers (230 and 213 kt N y −1 , 83 and 77 kg N ha −1 y −1 ); in contrast, Sweden used more synthetic (162 kt N y −1 , 54 kg N ha −1 y −1 ) than organic N (108 kt N y −1 , 36 kg N ha −1 y −1 ), with subnational variation in manure use as determined by livestock population. Livestock feed N intake was twice as large in Denmark (384 kt N y −1 ) as in Sweden (176 kt N y −1 ), reflecting Denmark’s larger livestock population. Denmark’s national crop NUE was lower (0.51) than Sweden’s (0.72), likely due to a lower proportion of grass–clover leys, higher N input rates, and more intensive production systems. However, considerable subnational variation existed in both countries. The livestock NUE was 0.29 in Denmark and 0.25 in Sweden; these differences are mainly due to a higher proportion of ruminants in Sweden with lower N feed use efficiency than pigs. Sweden emitted less N 2 O and NH 3 per unit area (∼56% for both gases) and in total (∼52% for both gases) than Denmark due to lower use of N inputs and less intensive farming systems. West Denmark and South Sweden were identified as emission hotspots. Our research provides essential information at subnational and national scales to improve N management and reduce gaseous N pollution, supporting the transition towards more sustainable agroecosystems in Denmark and Sweden.