Long-term effects of crop rotation and nitrogen management on nitrous oxide emissions in agricultural systems: a narrative review

Nitrous oxide (N 2 O) is a potent greenhouse gas with a global warming potential 265 to 298 times that of carbon dioxide over a century, and the principal anthropogenic stratospheric ozone-depleting substance now emitted to the atmosphere. Agricultural soils account for roughly 60% of anthropogenic emissions, so cropping sequence and nitrogen inputs directly shape emission rates. Drawing on 18 long-term field studies spanning 5 to 45 years and twelve countries, this review examines how crop rotation, tillage, organic and synthetic nitrogen fertilisation, and their interactions with soil and climate govern N 2 O across multi-decadal timescales. Management effects are rarely consistent across sites: no-till reduces emissions in well-drained temperate soils but raises them in waterlogged fine-textured soils, and organic fertilisers lower emissions when mineralisation matches crop uptake but raise them when labile carbon and nitrogen accumulate together. Mean N 2 O rises with temperature across studies, implying that warming will amplify emissions most in under-monitored tropical regions. The review identifies geographic gaps, inconsistent flux protocols, and weak integration of microbial ecology and process modelling as the main barriers to transferable guidance. Its contribution is a mechanistically grounded, management-organised synthesis that moves beyond aggregate effect sizes and proposes a research agenda for climate-smart nitrogen governance. This review is timely: as reactive-nitrogen use and global warming intensify together, and with N2O now the principal anthropogenic ozone-depleting substance emitted, it offers researchers, greenhouse-gas-inventory compilers and policymakers a transferable, mechanistically grounded basis for emission-reduction guidance across the diverse soils and climates where food is produced.