Clay-hydrochar composites mitigated CH4 and N2O emissions from paddy soil: A whole rice growth period investigation

Highlights: • Clay minerals were infused into hydrochars to obtain clay-hydrochar composite (CHC). • Three CHCs mitigated CH₄ and N₂O emissions by 21.4%–47.5% and 5.2%–36.8%. • Hydrochar mixed with kaolinite (KTHC) decreased greenhouse gas emission by 46.6%. • Mitigated greenhouse gas emissions might contribute to soil C and N retention. With the favorable microporous structure and excellent adsorption capacity, clay-hydrochar composites (CHCs) serve as promising materials to mitigate greenhouse gas emissions (GHG) from the paddy fields. Three clays were co-pyrolyzed with hydrochar derived from poplar sawdust to obtain CHCs, which were applied to the paddy fields to investigate the effects on methane (CH₄) and nitrous oxide (N₂O) emissions. Three CHCs were labeled as bentonite-hydrochar composite (BTHC), montmorillonite-hydrochar composite (MTHC), and kaolinite-hydrochar composite (KTHC), respectively. The effects of these three CHCs on GHG emissions were determined by monitoring the dynamic CH₄ and N₂O emissions in the paddy soil column ecosystem during the rice-growing season. The results showed that compared with the control group, three CHCs significantly mitigated CH₄ and N₂O emissions by 21.4%–47.5% and 5.2%–36.8%, respectively. Furthermore, the fluorescent components result displayed CHCs increased humic-like content by 29.62%–59.72%. A structural equation model was used to assess the hypothesis mitigation mechanism, which exemplified that GHG emissions negatively correlated with pmoA and nosZ genes, possibly resulting in the CH₄ and N₂O mitigation. Among the three CHCs, the KTHC amendment mitigated the CH₄ and N₂O emissions by 47.5% and 36.8%, respectively, which was superior to BTHC and MTHC. Hence, it was recommended for application to the field. Overall, this study demonstrates the mitigating effects of CHCs on GHG emissions for the first time, and the reduced CH₄ and N₂O emissions could contribute to increased soil C and N retention for better agricultural nutrients management.