Agricultural soils contribute ~52% of global anthropogenic nitrous oxide (N₂O) emissions, predominantly from nitrogen (N) fertilizer use. Global N₂O emission factors (EFs), estimated using IPCC Tier 1 methodologies, largely rely on short-term field measurements that ignore legacy effects of historic N fertilization. Here we show, through data synthesis and experiments, that EFs increase over time. Historic N addition increases soil N availability, lowers soil pH, and stimulates the abundance of N₂O producing microorganisms and N₂O emissions in control plots, causing underestimates of EFs in short-term experiments. Accounting for this legacy effect, we estimate that global EFs and annual fertilizer-induced N₂O emissions of cropland are 1.9% and 2.1 Tg N₂O-N yr⁻¹, respectively, both ~110% higher than IPCC estimates. Our findings highlight the significance of legacy effects on N₂O emissions, emphasize the importance of long-term experiments for accurate N₂O emission estimates, and underscore the need for mitigation practices to reduce N₂O emissions.

Global agriculture is facing multiple challenges to meet the food demands, optimize resource utilization, and mitigate the climate change. A field study, combined with the life cycle assessment (LCA), was conducted to select the effective and sustainable cropping systems in northwestern China. The study compared four maize‐based intercropping and corresponding monoculture systems on crop yield, evapotranspiration (ET), water use efficiency (WUE), profitability, and carbon footprint (CF). Maize/wheat intercropping had the highest energy yield (532.5 GJ/ha, on average) and maize equivalent energy yield (MEEY) (522.3 G/ha, on average), followed by those from the maize/rape intercropping system, and the lowest by the sole potato system. The WUE of maize equivalent energy yield (WUE_MEEY) was the highest (1.06 GJ ha⁻¹ mm⁻¹) for sole rape system, followed by those for the maize/wheat and maize/rape intercropping systems. Maize/potato intercropping had the highest benefit: cost ratio at 3.30, followed by those for the maize/wheat intercropping (2.58), sole potato (2.57), and maize/rape intercropping (2.53). Lower CF and higher net ecosystem economic budget (NEEB) were observed in maize‐based intercropping systems. The maize/wheat intercropping system had the lowest CF per maize equivalent energy yield (CF_m) (10.7 kg CO₂‐eq GJ⁻¹ year⁻¹), and the maize/potato intercropping system had the lowest CF per unit economic output (CF_e) (0.14 kg CO₂‐eq US$⁻¹ year⁻¹), and the highest NEEB (7,352.8 US$/ha). The data presented indicate that maize‐based intercropping system may be a viable practice for the synthesized goals of higher productivity and profitability while lesser environmental footprint in a water‐scarce region of northwest China.