Engineered biochar effects on methane emissions and rice yield under alternate wetting and drying in paddy soils

Abstract

Biochar is a promising strategy for improving crop yield and mitigating greenhouse gas emissions. However, the impacts of acid modified biochar on CH₄ emissions and yield in rice fields are not comprehensively understood, especially under alternate wetting and drying irrigation (I_AWD). Here, we conducted a 3-yr (2019-2021) field experiment with two irrigation regimes (I_CF: continuous flooding irrigation, I_AWD) and three biochar treatments (B₀: no biochar; B₂₀: 20 t ha⁻¹ rice straw biochar; and B_20A: 20 t ha⁻¹ acid modified rice straw biochar). Results showed I_AWD reduced CH₄ emissions by 63–80 % and water consumption by 10–12 % but threatened the rice soil fertility. B₂₀ and B_20A increased soil cation exchange capacity by 13–36 %, soil organic carbon by 24–44 % and C/N by 17–36 % over the three years. However, compared to B₀, B₂₀ tended to increase CH₄ emissions and factor (CH_4EF), reduced grain yield by 6 % in 2019, but B_20A suppressed CH₄ emissions by 19 % while maintaining a stable grain yield. B₂₀ and B_20A enhanced yield by 5 % and 8 %, 11 % and 12 % and decreased CH₄ emissions by 22 % and 38 %, 38 % and 40 % in 2020 and 2021, respectively. B_20A alleviated its initial negative impact on CH₄ emissions and yield in 2019 due to acid modified biochar enhancing more acidic and oxygenated functional groups. I_AWDB_20A decreased CH₄ emissions by 75–89 % and greenhouse gas emission intensity (GHGI) by 75–90 % compared to I_CFB₀ over the three years. Consequently, B_20A coupled with I_AWD achieves sustainable use of water resources, improves soil degradation and mitigates climate change.