Sustainable nitrogen management in maize: environmental benefits of integrating microbial biostimulants and nitrification inhibitors

Biostimulants and nitrification inhibitors are promising tools to improve nitrogen dynamics in agricultural soils and reduce associated environmental impacts. In Europe, these solutions are increasingly promoted to improve nitrogen use efficiency and losses, yet farm-level evidence of their combined environmental performance in maize remains limited. This study evaluated whether applying a microbial biostimulant (Methylobacterium symbioticum SB23) with a nitrapyrin-based nitrification inhibitor can mitigate the environmental impacts of maize in Italy. A cradle-to-farm-gate LCA was performed on 14 farms, comparing a conventional scenario (CS) with an alternative scenario (AS) applying the two products while reducing mineral N fertilization. Three functional units were assessed: 1 tonne maize grain (14% moisture), 1 tonne high-moisture corn (25% DM), and 1 tonne fresh chopped maize (35% DM). Inventory modelling combined primary on-farm data from questionnaires and interviews with secondary data, including Brentrup's N balance for N emissions. Across farms and functional units, AS generally lowered nitrogen-driven categories, climate change, acidification, particulate matter formation, and terrestrial eutrophication, reflecting reduced mineral N inputs and inhibited nitrification. For grain, 10 of 11 impact categories decreased (−2% to −50%); for high-moisture corn, 8 of 11 decreased (−1% to −87%); and for silage, 10 of 11 decreased (−1% to −83%). Trade-offs emerged: marine eutrophication occasionally increased where fertilizer reductions were limited and the biostimulant enhanced soil N availability, increasing NO3- leaching. Contribution analysis confirmed category hotspots: NH3 volatilization for acidification, particulate matter, and terrestrial eutrophication, N2O for climate change, NO3− leaching for marine eutrophication, and crop protection products for freshwater ecotoxicity. Overall, integrating a microbial biostimulant with a nitrification inhibitor can substantially reduce most impacts of maize cultivation.