Two-fifths organic substitution reduces yield-scaled footprint and enhances net ecosystem carbon budget of sorghum production in saline-alkali soil

Long-term overuse of synthetic N fertilizers has exacerbated environmental degradation in vulnerable ecosystems and intensified global warming. Partial substitution of synthetic N with manure presents a viable agronomic strategy to mitigate these ecological pressures. This study evaluated the effects of prolonged organic substitution (40 % and 60 % replacement of synthetic N with aged cow manure, termed OS40 and OS60) on greenhouse gas (GHG) emissions, carbon footprint (CF), and carbon budget in a saline-alkali sorghum cropping system under drip irrigation with plastic film mulching. Four treatments were tested over two growing seasons: no fertilizer (N0), synthetic N alone (180 kg ha⁻¹, N180), synthetic N replaced with aged cow manure at ratios of 40 % (OS40) and 60 % (OS60). Results demonstrated that OS40 and OS60 significantly reduced cumulative N 2 O and CH 4 emissions by 24.6–27.2 % and 45.6–60.7 %, respectively, compared to N180, though cumulative CO₂ emissions increased by 22.6–48.4 %. Consequently, the net global warming potential (NGWP) decreased by 40.9 % (OS40) and 51.2 % (OS60), with yield-scaled CF reduced by 27.9 % and 26.8 %, respectively. Notably, OS40 enhanced soil organic carbon (SOC) storage and net primary productivity (NPP) by 9.5 % and 13.4 %, respectively, while maintaining comparable grain yields to N180. The net ecosystem carbon budget (NECB) increased proportionally with higher manure substitution rates, with OS40 achieving optimal balance between GHG mitigation (NGWP intensity reduced by 47.0 %) and carbon sequestration efficiency. These findings highlight that a 40 % substitution ratio effectively reduces the CF, enhances SOC accumulation, and sustains crop productivity, offering a sustainable strategy for saline-adaptive sorghum production systems. • Carbon budget and carbon footprint were fully evaluated in a salt-affected agroecosystem. • Organic substitution decreased N 2 O and CH 4 emission but increased CO 2 emission. • Organic substitution decreased net global warming potential intensity by 41–51 % • Sorghum grain yield-scaled carbon footprint reduced by 26–28 % by organic substitution. • 40 % organic substitution of chemical nitrogen had the higher net ecosystem carbon budget.