One-third substitution of nitrogen with cow manure or biochar greatly reduced N2O emission and carbon footprint in saline-alkali soils

The rapid expansion of farmland and long-term excessive nitrogen (N) application have caused huge environmental risks in fragile ecosystems facing global warming. Partially substituting N fertilizer with organic fertilizers offers an alternative field management strategy to alleviate the pressure of the ecological environment. To this end, the influence of one-third substitution of N fertilizer with cow manure or biochar field experiment was conducted under maize in Tarim River Basin since 2019. Five treatments with three replications were applied: CK (Fallow); no fertilization (0 N); conventional N fertilizer (N; N: 300 kg N ha- 1, organic fertilizer: 0 kg N ha- 1); one-third substitution of N with biochar (NB; N: 200 kg N ha- 1, Biochar: 100 kg N ha- 1) and one-third substitution of N with cow manure (NM; N: 200 kg N ha- 1, Cow manure: 100 kg N ha- 1) under maize season in saline-alkali soils. The greenhouse gas (GHG) emissions, net ecosystem carbon budget (NECB), soil organic carbon (SOC), maize yield, carbon footprint (CF), and yield carbon footprint (CFy) were analyzed from 2021 to 2022. The results showed that NB treatment decreased the average cumulative CO2 emissions by 21 %, while NM treatment showed no difference compared to N treatment. NB and NM treatments reduced the average cumulative N2O emissions (-61 %, -49 %), CF (-68 %, -10 %), CFy (-66 %, -19 %) and increased maize yield (+3 %, +2 %), SOC storage (+43 %, +6 %), NECB (+80 %, +24 %), and agronomic N use efficiency (ANUE) (+5 %, +3 %), compared to N treatment. NB treatment had the lowest emission factors (EF) (0.19 %) and the highest sustainability index (1.58) compared to NM treatment (0.26 %, 0.61) and N treatment (0.53 %, 0.84). To sum up, substituting one-third of N fertilizer with biochar or manure in saline-alkali soils was proved to be a multi-benefit strategy to increase yields and reduce GHG emissions and CF.