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

Abstract

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 (CF_y) 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 %), CF_y (−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.