Biochar rather than organic fertilizer mitigated the global warming potential in a saline-alkali farmland

A 3-year field study was conducted to examine the effects of continuous application of biochar and organic fertilizer on global warming potential (GWP) and greenhouse gas intensity (GHGI) as well as crop yield in a saline-alkali farmland of northern China. Six treatments were included: 1) control (only chemical fertilizer with N200 kg ha⁻¹ yr–¹ and P₂O₅ 120 kg ha⁻¹ yr–¹, CK); 2) biochar at 5.0 t ha–¹ yr–¹ (C1); 3) biochar at 10.0 t ha–¹ yr–¹ (C2); 4) biochar at 20.0 t ha–¹ yr–¹ (C3); 5) organic fertilizer at 7.5 t ha–¹ yr–¹ (M1); and 6) organic fertilizer at 10.0 t ha–¹ yr–¹ (M2). Biochar and organic fertilizer treatments were adjusted to the same N and P level as the control by supplemented urea and diammonium phosphate. The results showed that both biochar and organic fertilizer reduced the annual average emissions of CH₄, N₂O and ecosystem respiration (Rₑ), but the emissions from the biochar treatments were lower than those from the organic fertilizer treatments. Biochar but not organic fertilizer increased the maize and wheat yields. Both biochar and organic fertilizer increased the soil carbon (C) storage and the net ecosystem carbon budget (NECB). The ΔSOCs of biochar and organic fertilizer treatments were increased by 9.1%–16.5% and 5.0%–5.8%, respectively, compared with the control (1.21 t C ha⁻¹ yr⁻¹). The mean annual net GWPs of biochar and organic fertilizer treatments were decreased by 282.5%–365.0% and 89.2%–110.0%, respectively, compared with the control (1.2 t CO₂-eq ha⁻¹ yr⁻¹). The GHGIs were decreased by 266.7%–344.4% and 88.9%–110.0%, respectively, compared with the control (0.09 t CO₂-eq ha⁻¹ yr⁻¹). The net GWPs and GHGIs were significantly lower in the C2 and C3 than other treatments, but there was no significant different between C2 and C3. The N₂O emissions and ΔSOC contributed greatly to the net GWP, therefore, controlling soil N₂O emissions and increasing soil C storage are key components of reducing net GWP and GHGI. In conclusion, application of biochar is an effective agricultural practice to improve soil quality, increase crop yield and reduce greenhouse gases (GHGs) emissions in the saline-alkali soil of northern China.