Evaluating the potential of legumes to mitigate N2O emissions from permanent grassland using process-based models

Authors: FUCHS, KATHRIN - Institute Of Agricultural Sciences; MERBOLD, LUTZ - International Livestock Research Institute (ILRI) - Kenya; BUCHMANN, NINA - Institute Of Agricultural Sciences; BELLOCCHI, GIANNI - Vetagro Sup; MARTIN, RAPHAEL - Vetagro Sup; KLUMPP, KATJA - Vetagro Sup; BINDI, MARCO - University Of Florence; BRILLI, LORENZO - University Of Florence; CONANT, RICHARD - Colorado State University; DORICH, CHRISTOPHER - Colorado State University; EHRHARDT, FIONA - Inland Northwest Research Alliance, Inra; SOUSSANA, JEAN-FRANCOIS - Inland Northwest Research Alliance, Inra; FITTON, NUALA - University Of Aberdeen; SMITH, PETE - University Of Aberdeen; GRACE, PETER - Queensland University Of Technology; Liebig, Mark; LIEFFERING, MARK - Agresearch; NEWTON, PAUL - Agresearch; REES, ROBERT - Sruc-Scotland'S Rural College; TOPP, CAIRISTIONA - Sruc-Scotland'S Rural College; RECOUS, SYLVIE - Inland Northwest Research Alliance, Inra; SNOW, VAL - Agresearch

Submitted to: Global Biogeochemical Cycles
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2020
Publication Date: 11/27/2020
Citation: Fuchs, K., Merbold, L., Buchmann, N., Bellocchi, G., Martin, R., Klumpp, K., Bindi, M., Brilli, L., Conant, R.T., Dorich, C.D., Ehrhardt, F., Soussana, J., Fitton, N., Smith, P., Grace, P., Liebig, M.A., Lieffering, M., Newton, P.C., Rees, R.M., Topp, C.F., Recous, S., Snow, V. 2020. Evaluating the potential of legumes to mitigate N2O emissions from permanent grassland using process-based models. Global Biogeochemical Cycles. 34. Article e2020GB006561. https://doi.org/10.1029/2020GB006561.
DOI: https://doi.org/10.1029/2020GB006561

Interpretive Summary: Nitrous oxide (N2O) is the third most important greenhouse gas in terms of its global warming effect. Strategies to reduce N2O from grassland soils include the use of legumes, which can substitute nitrogen (N) fixed from the atmosphere for N fertilizer. Legumes can also provide an N source that is better synchronized to plant demand than infrequent fertilizer applications. Despite these advantages, the potential to reduce N2O emissions with legumes is still relatively untested. Our objectives were: (1) to assess the effects of a wide range of legume proportions and N fertilizer amounts on yields, N2O emissions and N2O emission intensities, and (2) to identify an optimal N2O reduction strategy. Two variants of two process-based models (APSIM and DayCent) were used to test the potential to reduce N2O while maintaining pasture production for five temperate grassland sites across the globe. All models showed that replacing fertilizer with legumes could reduce N2O emissions without reducing biomass yield across a broad range of fertilizer-legume combinations. The results are useful to policy makers and scientists in identifying potential methods to reduce N2O emissions.

Technical Abstract: A potential strategy for mitigating nitrous oxide (N2O) emissions from permanent grasslands is the partial substitution of fertilizer nitrogen (Nfert) with symbiotically fixed nitrogen (Nsymb) from legumes. The input of Nsymb reduces the energy costs of producing fertilizer and is likely to provide a supply of nitrogen (N) for plants that is more synchronous to plant demand than occasional fertilizer applications. Legumes have been promoted as a potential strategy for the mitigation of N2O from grassland but evidence to support their efficacy is limited partly due to the difficulty in conducting experiments across the range of potential combinations of legume proportions and fertilizer N input. These experimental constraints can be overcome, and targeted experiments designed, by the use of biogeochemical models that can ‘experimentally’ vary legume/fertilizer combinations with ease. Using two variants of two process-based biogeochemical models (APSIM and DayCent) we tested the N2O mitigation potential and pasture production of full factorial combinations of legume proportion and fertilizer rate for five temperate grassland sites across the globe. All the models showed that replacing fertilizer with legumes could reduce N2O emissions without reducing biomass yield across a broad range of fertilizer-legume combinations. Although the models were consistent in the relative changes in N2O emissions to a baseline scenario (300 kg N-1 yr-1 with no legume) they predicted different levels of absolute N2O emissions and N2O emissions reductions; both were greater in DayCent than in APSIM.