Biochar type and rate effects on greenhouse gas emissions from furrow-irrigated rice

Biochar is a relatively new, potential climate-mitigation strategy, but biochar still requires investigation regarding biochar's ability to reduce greenhouse gas (GHG) emissions. Little research has been conducted to quantify the impacts of biochar on GHG production from upland (i.e., furrow-irrigated) rice (Oryza sativa) production systems. The objective of this study was to evaluate the effects of wood biochar type (powder and coarse particle size) and application rate (0, 2.5, and 5 Mg ha⁻¹) on GHG emissions in greenhouse-grown, simulated furrow-irrigated rice grown in a silt-loam soil. Carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) fluxes were measured weekly throughout a 5-month growing season during summer 2023, and season-long emissions and reduced global warming potential (GWP, excluding CO₂) were estimated. Among the coarse-sized biochar treatments, season-long N₂O emissions (41.7 kg N₂O ha⁻¹ season⁻¹) were largest (p < 0.05) from the unamended control (0 Mg ha⁻¹), followed by the 2.5 (17.1 kg N₂O ha⁻¹ season⁻¹) and 5 Mg ha⁻¹ rate (4.9 kg N₂O ha⁻¹ season⁻¹), while season-long N₂O emissions did not differ (p > 0.05) among powder-sized biochar treatments. Reduced GWP was greatest (p < 0.05; 11.2 Mg CO₂ eq. ha⁻¹ season⁻¹) from the unamended control, followed by the 2.5 Mg ha⁻¹ rate (4.7 Mg CO₂ eq. ha⁻¹ season⁻¹), and least (p < 0.05; 1.4 Mg CO₂ eq. ha⁻¹ season⁻¹) from the 5 Mg ha⁻¹ rate of coarse biochar. Results showed that coarse-sized, wood-chip biochar has the potential to mitigate N₂O emissions from furrow-irrigated rice in a silt-loam soil.